Percent Shortening Research Articles

Time-dependent changes in matrix metalloproteinase activity and expression during the progression of congestive heart failure: relation to ventricular and myocyte function.

The development of congestive heart failure (CHF) is associated with left ventricular (LV) dilation and myocardial remodeling. However, fundamental mechanisms that contribute to this remodeling process with the progression of CHF remain unclear. The matrix metalloproteinases (MMPs) have been demonstrated to play a significant role in tissue remodeling in a number of pathological processes. The present project tested the hypothesis that the LV dilation and remodeling during the progression of CHF is associated with early changes in MMP expression and zymographic activity. LV and myocyte function, collagen content, and MMP expression and zymographic activity were serially measured during the progression of CHF caused by pacing-induced supraventricular tachycardia (SVT) in pigs. After 7 days of SVT, LV end-diastolic dimension and myocyte length both increased by 15% from control values, and LV fractional shortening fell by 20%. At the level of the myocyte, percent shortening fell by 16% after 7 days of SVT, with no change in the steady-state velocity of shortening. Longer durations of SVT caused progressive LV dilation, LV pump failure, and myocyte contractile dysfunction. Specifically, 21 days of SVT resulted in a >50% increase in LV dimension, a 56% fall in LV fractional shortening, and a 33% decline in myocyte velocity of shortening. The decline in LV and myocyte function with 21 days of SVT was accompanied by signs and symptoms of CHF. Thus, SVT causes time-dependent changes in LV geometry and function and the subsequent development of CHF. LV myocardial collagen content and confluence fell by >25% after 7 days of SVT and were accompanied by an 80% increase in LV myocardial MMP zymographic activity against the substrate gelatin. After 14 days of SVT, total LV myocardial collagen content was reduced by 24%, and LV myocardial MMP zymographic activity increased by >100% from control values. Interstitial collagenase (MMP-1), stromelysin (MMP-3), and 72-kD gelatinase (MMP-2) were increased by approximately 2-fold after 7 days of SVT. LV MMP zymographic activity and abundance remained elevated with longer durations of SVT. The results of the present study demonstrated that in this model of CHF, early changes in LV myocardial MMP zymographic activity and protein levels occurred with the initiation and progression of LV dilation and dysfunction. These findings suggest that an early contributory mechanism for the initiation of LV remodeling that occurred in this model of developing CHF is enhanced expression and potentially increased activity of LV myocardial MMPs.

Impaired G protein function in gallbladder muscle from progesterone-treated guinea pigs.

This study was designed to elucidate the mechanism of action of progesterone on gallbladder smooth muscle in guinea pigs. Adult male guinea pigs were treated with either progesterone (2 mg.kg-1.day-1) or saline for 7 days. Gallbladder muscle cells were isolated by enzymatic digestion with collagenase. Contractile responses to agonists were expressed as percent shortening from control cell length. [35S]guanosine 5'-O-(3-thiotriphosphate) ([35S]GTP gamma S)-binding properties of G proteins were assessed in crude membranes of gallbladder muscle with or without cholecystokinin octapeptide (CCK-8) stimulation. Gallbladder muscle cells from progesterone-treated guinea pigs exhibited an impaired contractile response to CCK-8, GTP gamma S, or aluminum fluoride but a normal response to potassium chloride or D-myo-inositol 1,4,5-trisphosphate compared with controls. Western blot analysis of gallbladder muscle revealed the presence of Gi1-2, Gi3, Gq/11, and Gs proteins. The maximal contraction induced by CCK-8 was blocked by pertussis toxin and Gi alpha 3-specific antibodies, but not by Gi alpha 1-2 or Gq/11 alpha antibodies. CCK-8 caused a significant increase in [35S]GTP gamma S binding to Gi alpha 3, but not to Gq/11 alpha or Gi alpha 1-2. The stimulation of Gi alpha 3 binding, however, was significantly reduced in gallbladder muscle membranes from progesterone-treated guinea pigs compared with that in control animals. In conclusion, progesterone might cause gallbladder hypomotility by downregulating Gi3 proteins.

Physical, contractile and calcium handling properties of neonatal cardiac myocytes cultured on different matrices.

Extracellular matrix components play a vital role in the determination of heart cell growth, development of spontaneous contractile activity and morphologic differentiation. In this work we studied the physical and contractile changes in neonatal rat cardiac myocytes over the first four days of growth on three different extracellular matrices. We compared commercial laminin and fibronectin, plus a fibroblast-derived extracellular matrix, which we have termed cardiogel. Myocytes cultured on cardiogel were characterized by greater cellular area and volume when compared to cells cultured on the other single-component matrices. Spontaneous contractile activity appeared first in the cells grown on cardiogel, sometimes as early as the first day post-plating, in contrast to day three in the cells cultured on laminin. Measurements of cardiac myocyte contractility i.e. percent shortening and time to peak contraction, were made on each of the first four days in each culture. Myocytes cultured on cardiogel developed maximum shortening more rapidly than the other cultures, and an earlier response to electrical pacing. Histochemical staining for myocyte mitochondrial content, revealed that the cardiogel-supported cells exhibited the earliest development of this organelle and, after four days, the greatest abundance. This reflects both a greater cell size, as well as response to increasing energy demands. Due to the increase in volume and contractile activity exhibited by the cardiogel grown myocytes, we employed calcium binding and uptake experiments to determine the comparative cellular capacities for calcium and as an indicator of sarcoplasmic reticulum development. Also whole cell phosphorylation in the presence of low detergent was assayed, to correlate calcium uptake with phosphorylation, in an attempt to examine possible increases in calcium pump number and other phosphorylatable proteins. In agreement with our physical and contractile data, we found that the cells grown on cardiogel showed a greater calcium uptake over the first four days of culture, and increased phosphorylation. However, calcium binding was not dramatically different comparing the three culture matrices. Based on our data, the fibroblast-derived cardiogel is the matrix of choice supporting earliest maturation of neonatal cardiomyocytes, in terms of spontaneous contractions, calcium handling efficiency, cell size and development of a subcellular organelle, the mitochondrion.

Left ventricular function and endomyocardial biopsy in early and advanced dilated cardiomyopathy

We evaluated left ventricular function and endomyocardial biopsy in 20 patients with early and advanced dilated cardiomyopathy, with the purpose of assessing the correlation between histologic variables and systolic and diastolic filling indexes. Group 1 included 10 patients with no clinical history of heart failure and left ventricular ejection fraction ≥45% and group 2, 10 patients with a clinical history of heart failure and left ventricular ejection fraction <45%. Group 1 showed lower left ventricular end-systolic and end-diastolic volumes indexes (49±14 versus 86±23 ml/m 2, P<0.001; 98±25 versus 127±35 ml/m 2, P=0.049), higher left ventricular ejection fraction (50±4 versus 32±4%, P<0.001) and lower coefficient of variation of percentage shortening of left ventricular transverse hemiaxes (0.3±0.1 versus 0.5±0.1, P=0.001) compared with group 2. Group 1 had higher A wave peak velocity (78±18 versus 60±20 cm/s, P=0.048), lower E/A ratio (0.9±0.3 versus 1.5±0.6, P=0.02) and slower E wave deceleration time (204±51 versus 155±50 ms, P=0.047) compared with group 2. Semiquantitative histologic scores did not differ significantly between groups. There was no significant correlation between histologic variables and left ventricular systolic and diastolic indexes. Thus, dilated cardiomyopathy shows borderline to severe left ventricular systolic impairment and distinct left ventricular diastolic filling abnormalities, according to the clinical stage. This study suggests a marked dissociation between histologic findings and functional abnormalities in early and advanced dilated cardiomyopathy.

Electrophysiologic effects of quinaprilat in dogs during acute myocardial ischemia and following reperfusion

Background There have been few studies concerning the electrophysiologic changes associated with the use of angiotensin-converting enzyme inhibitors in patients with acute myocardial infarction. We examined the electrophysiologic effects of quinaprilat in dogs during acute myocardial ischemia and following reperfusion. Methods The left anterior descending coronary artery was occluded for 10 min and reperfused for 10 min. Animals received intravenous quinaprilat (3 μg/kg per min, quinaprilat group) or saline (control group). We measured the ventricular effective refractory period and intra-myocardial conduction time within the left anterior descending coronary artery region (ischemic region) during myocardial ischemia and following reperfusion, and determined the frequency of ventricular fibrillation. Results The effective refractory period in the ischemic region decreased during myocardial ischemia, and decreased further immediately after reperfusion in the control group. The intra-myocardial conduction time in the ischemic region increased during myocardial ischemia but rapidly shortened after reperfusion in the control group. In the quinaprilat group, however, no significant differences were evident between the ischemic and non-ischemic regions in either the effective refractory period or the intra-myocardial conduction time during myocardial ischemia or following reperfusion. The percentage shortening of the effective refractory period and the percentage prolongation of the intra-myocardial conduction time in the ischemic region were significantly lower in the quinaprilat group than in the control group during myocardial ischemia and following reperfusion. The frequency of ventricular fibrillation during myocardial ischemia and following reperfusion was significantly lower in the quinaprilat group (21%) than in the control group (74%; P < 0.01). Conclusions Quinaprilat protects against electrophysiologic abnormalities, and may decrease arrhythmias during acute myocardial ischemia and following reperfusion.

Cytosolic Ca2+ concentration and contraction-relaxation properties of ventricular myocytes from Escherichia coli endotoxemic guinea pigs: effect of fluid resuscitation.

Hearts isolated from a guinea pig model of Escherichia coli endotoxemia exhibit decreased systolic contractile function and reduced diastolic compliance of the left ventricle within 4 h after injection of endotoxin. Fluid resuscitation prevented the endotoxin-induced decrease in diastolic compliance without affecting systolic contractile depression. Because intrinsic myocardial dysfunction after endotoxemia may result from alterations in intracellular Ca2+ handling, we tested the hypothesis that in vivo fluid resuscitation improved diastolic function by altering Ca2+ handling of the myocardium. We tested this hypothesis by measuring cell shortening and intracellular Ca2+ of ventricular myocytes isolated from endotoxemic guinea pigs. E. coli endotoxin (LPS, 1 mg/kg)-injected guinea pigs were divided into resuscitated and nonresuscitated groups. Fluid resuscitated animals received a Ringer's infusion (8 mL.kg-1.h-1) intravenously (i.v.) beginning immediately after endotoxin injection. Four hours later, ventricular myocytes were isolated enzymatically and loaded with fura-2/AM. When myocytes were field stimulated at .8 Hz, peak systolic Ca2+ transients of LPS-resuscitated (619 +/- 75 nM) and LPS-nonresuscitated (599 +/- 60 nM) myocytes were not significantly different from each other, but both were significantly less than values from control myocytes (1187 +/- 118 nM, p < .05). The percentage of cell shortening of LPS-resuscitated (6.2 +/- .9%) and LPS-nonresuscitated (6.2 +/- .3%) myocytes were also less than control (11.8 +/- .5%, p < .05). In contrast to improved diastolic compliance of fluid-resuscitated hearts, diastolic [Ca2+]i of myocytes (at .8 Hz) from LPS-resuscitated animals (138 +/- 47 nM) was not statistically different from LPS-nonresuscitated animals (129 +/- 19 nM). Diastolic values of both LPS groups were consistently lower than control value (251 +/- 38 nM, p < .05). These data suggest that improved diastolic compliance of LPS hearts following fluid resuscitation is not associated with improved myocyte contractility or myoplasmic Ca2+ handling.

Left Ventricular Hypertrophy in Hypertensive Patients Is Associated With Abnormal Rate Adaptation of QT Interval

Objectives. This study sought to examine whether the responses of the QT interval to changes in the heart rate were altered in left ventricular hypertrophy (LVH).Background. The QT interval has been shown to have a delayed adaptation to sudden changes in heart rate in normal subjects. Abnormalities in the adaptation of the QT interval to changes in the RR interval may facilitate the development of ventricular arrhythmias.Methods. Consecutive newly diagnosed hypertensive subjects, not taking any medications, were age and gender matched for LVH (n = 21) versus no LVH (n = 16). QT interval dynamics were analyzed under visual control using a validated algorithm with automatic QT measurements at the end of the T wave. A computerized Holter system was developed to study the QT interval response to changes in the RR interval. The adaptive response of the QT interval was measured as the ratio of the slope from 10% to 90% of the QT change relative to the RR interval change (dQT/dRR10–90). Steady state adaptation was also studied as the percent shortening and lengthening of the QT interval during acceleration and deceleration of heart rate.Results. The adaptive response of the QT interval measured as dQT/dRR10–90was increased in the LVH group compared with that in the control subjects during both acceleration (0.33 ± 0.06 vs. 0.18 ± 0.02, p = 0.02) and deceleration phases (0.23 ± 0.04 vs. 0.16 ± 0.02, p = 0.03). In the LVH group, the percent lengthening of the QT interval was greater (7.6 ± 0.7 vs. 5.1 ± 0.2, p = 0.03), whereas the percent shortening was not significantly different (5.71 ± 0.5 vs. 4.6 ± 0.3, p = 0.43), than that in control subjects.Conclusions. The QT interval response to changes in the RR interval is rapid and exaggerated in LVH. These abnormalities of the QT interval response demonstrate that there are altered repolarization dynamics in patients with LVH that may make them vulnerable to serious ventricular arrhythmias.(J Am Coll Cardiol 1997;29:778–84)

Differential effects of novel protamine variants on myocyte contractile function with left ventricular failure

Background. Protamine administration can cause left ventricular (LV) dysfunction, which may have clinical significance in the setting of congestive heart failure (CHF). Protamine variants have recently been constructed with heparin reversal capacity similar to protamine. The purpose of this study was to examine the potential differential effects of these protamine variants on isolated myocyte contractile function in normal myocytes and in myocytes after the development of CHF. Methods. Contractile function was measured by means of computer-aided videomicroscopy in myocytes from five normal pigs and five pigs with CHF induced by rapid pacing (240 beats/min for 3 weeks). Myocyte contractility was examined in the presence of 40 μg/ml native protamine or one of three protamine variants: (1) reduced charge (+18) and lysine substituted for arginine; (2) lysine-substituted variant with glutamic acid substituted for the initial proline; or (3) arginine-rich peptide with a terminal arginine-glycine-aspartic acid (RGD) amino acid sequence. Results. In the presence of native protamine, myocyte percent shortening fell from baseline in both the normal (2.86 ± 0.15 versus 4.58 ± 0.08, p < 0.05) and the CHF groups (1.01 ± 0.06 versus 2.07 ± 0.05, p < 0.05). With both of the lysine-substituted protamine variants, percent shortening fell from baseline in the normal group (3.42 ± 0.20 for arginine and 3.74 ± 0.20 for glutamic acid versus 4.58 ± 0.08, p < 0.05), and was unchanged in the CHF group (1.94 ± 0.13 versus 2.07 ± 0.05, p = 0.34 for arginine; and 1.96 ± 0.10 versus 2.07 ± 0.05, p = 0.31, for glutamic acid). However, with the arginine/RGD variant, percent shortening fell from baseline in both the normal (2.86 ± 0.23 versus 4.58 ± 0.08, p < 0.05) and the CHF groups (1.32 ± 0.10 versus 2.07 ± 0.05, p < 0.05). Conclusions. Specific changes in the primary and secondary structures of protamine had different effects on myocyte contractile function. Furthermore, the negative effects of ly sine-substituted protamine variants on myocyte contractility were less pronounced in both CHF and normal myocytes. Thus protamine variants may be of clinical use, particularly in the setting of preexisting LV dysfunction.

Remote Noninfarcted Region Dysfunction Soon After First Anterior Myocardial Infarction

Previous studies have demonstrated hyperkinetic endocardial motion of noninfarcted myocardium early after myocardial infarction (MI). We wished to substantiate the findings of increased function of remote noninfarcted regions using magnetic resonance (MR) myocardial tagging in patients soon after anterior MI. Twenty-eight patients (25 male; mean age, 52 years) were studied on day 5 +/- 2 after first anterior MI. All had single-vessel left anterior descending coronary artery (LAD) disease and had received reperfusion therapy but had evidence of regional left ventricular (LV) dysfunction and an ejection fraction (EF) < or = 50%. Breath-hold, segmented k-space, gradient-echo MR tagging was performed with short-axis imaging spanning the LV. Percent circumferential shortening (%S) on a topographic basis, LV mass, and EF were measured. Regional %S was compared with that in 10 normal subjects (7 male; mean age, 43 years). We found reduced intramyocardial %S throughout the LV in the patient group. Percent shortening was lower in patients compared with control subjects at all sites along the long axis of the ventricle (9 +/- 5% versus 23 +/- 3% at the apex, P < .0001; 11 +/- 5% versus 21 +/- 3% at the midventricle, P < .0001; 14 +/- 3% versus 17 +/- 5% at the base, P < .02). The basal lateral and midinferior regions, remote from LAD territory, demonstrated reduced %S and a strong trend toward reduced %S, respectively. Patients on day 5 after first anterior MI with single-vessel disease demonstrate reduced intramyocardial circumferential shortening throughout the LV, including remote noninfarcted regions. Potential mechanisms include altered coronary vasodilatory properties, changes in regional mechanical load, or mechanical tethering to infarcted regions.

Endogenous Basal Nitric Oxide Production Does Not Control Myocardial Oxygen Consumption or Function

Previous studies from our laboratory have shown that an extrinsic nitric oxide (NO) donor (i.e., nitroprusside) caused vasodilatation and negative inotropy by activating guanylate cyclase and increasing myocardial cyclic GMP. We tested the hypothesis that endogenous myocardial NO production would limit myocardial oxygen consumption and function in vivo. We used the NO synthase inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-monomethyl-L-arginine (L-NMMA) in nine open-chest anesthetized mongrel dogs. Either L-NAME (6 mg/kg) or L-NMMA (3 mg/kg) were infused into the left anterior descending coronary artery (LAD). The circumflex (CFX) coronary artery region served as a control. Regional segment work was calculated as the integrated product of local force (miniature transducer) and segment shortening (ultrasonic crystals). Local myocardial O2 consumption was determined using an ultrasonic LAD flow probe and local arterial-venous O2 content difference (oximetry). Cyclic GMP levels were obtained via a radioimmunoassay. Both L-NAME and L-NMMA caused a local decrease in coronary blood flow (LAD flow: 80 +/- 8 to 69 +/- 7 ml/min/100 g [means +/- SEM]) and increased O2 extraction (9.1 +/- 0.6 to 10.2 +/- 0.7 ml O2/100 ml). However, this led to no change in local O2 consumption. LAD segment force was not altered (12.1 +/- 0.7 to 11.6 +/- 0.9 g), nor was the percent shortening changed (10.8 +/- 1.8% to 10.0 +/- 1.4%) by L-NAME or L-NMMA, leading to no net change in segment work. Myocardial cyclic GMP levels were not different in a comparison between the LAD (1.7 +/- 0.4 pmoles/g) and control (1.7 +/- 0.2) regions with either L-NAME or L-NMMA. We conclude that blockade of endogenous NO production with L-NAME and L-NMMA is sufficient to cause vasoconstriction in the heart of anesthetized dogs. However, this dose did not lead to alteration in local myocardial function, O2 consumption, or cyclic GMP levels.

Preservation of myocyte contractile function after hypothermic, hyperkalemic cardioplegic arrest with 2,3-butanedione monoxime

One proposed contributory mechanism for depressed ventricular performance after hypothermic, hyperkalemic cardioplegic arrest is a reduction in myocyte contractile function caused by alterations in intracellular calcium homeostasis. Because 2,3-butanedione monoxime decreases intracellular calcium transients, this study tested the hypothesis that 2,3-butanedione monoxime supplementation of the hyperkalemic cardioplegic solution could preserve isolated myocyte contractile function after hypothermic, hyperkalemic cardioplegic arrest. Myocytes were isolated from the left ventricles of six pigs. Magnitude and velocity of myocyte shortening were measured after 2 hours of incubation under normothermic conditions (37º C, standard medium), hypothermic, hyperkalemic cardioplegic arrest (4º C in Ringer's solution with 20 mEq potassium chloride), and hypothermic, hyperkalemic cardioplegic arrest with 2,3-butanedione monoxime supplementation (4º C in Ringer's solution with 20 mEq potassium chloride and 20 mmol/L 2,3-butanedione monoxime). Because β-adrenergic agonists are commonly employed after cardioplegic arrest, myocyte contractile function was examined in the presence of the β-agonist isoproterenol (25 nmol/L). Hypothermic, hyperkalemic cardioplegic arrest and rewarming reduced the velocity (32%) and percentage of myocyte shortening (27%, p < 0.05). Supplementation with 2,3-butanedione monoxime normalized myocyte contractile function after hypothermic, hyperkalemic cardioplegic arrest. Although β-adrenergic stimulation significantly increased myocyte contractile function under normothermic conditions and after hypothermic, hyperkalemic cardioplegic arrest, contractile function of myocytes exposed to β-agonist after hypothermic, hyperkalemic cardioplegic arrest remained significantly reduced relative to the normothermic control group. Supplementation with 2,3-butanedione monoxime restored β-adrenergic responsiveness of myocytes after hypothermic, hyperkalemic cardioplegic arrest. Thus, supplementation of a hyperkalemic cardioplegic solution with 2,3-butanedione monoxime had direct and beneficial effects on myocyte contractile function and β-adrenergic responsiveness after cardioplegic arrest. A potential mechanism for the effects of 2,3-butanedione monoxime includes modulation of intracellular calcium transients or alterations in sensitivity to calcium. Supplementation with 2,3-butanedione monoxime may have clinical utility in improving myocardial contractile function after hypothermic, hyperkalemic cardioplegic arrest. (J T HORAC C ARDIOVASC S URG 1996;111:621-9)

Annexin VI overexpression targeted to heart alters cardiomyocyte function in transgenic mice.

Annexin VI is a member of a family of Ca(2+)-dependent phospholipid-binding proteins that is expressed in many tissues, including the heart. It is a regulator of membrane-associated events, including the skeletal muscle ryanodine-sensitive Ca2+ release channel and the cardiac Na+/Ca2+ exchanger. The potential roles of annexin VI in Ca2+ signaling in cardiac myocytes were evaluated by targeting its overexpression to the hearts of transgenic mice. Expression of full-length human annexin VI cDNA was targeted to the heart using the alpha-myosin heavy chain gene promoter (Subramaniam, A., W. K. Jones, J. Gulick, S. Wert, J. Neumann, and J. Robbins. J. Biol. Chem. 266: 24613-24620, 1991). Five transgenic lines exhibited at least 10-fold overexpression of annexin VI protein in both atria and ventricles. Pathological evaluation indicated mice overexpressing annexin VI had enlarged dilated hearts, acute diffuse myocarditis, lymphocytic infiltration, moderate to severe fibrosis throughout the heart, and mild fibrosis around the pulmonary veins of the lungs. Contractile mechanics of cardiomyocytes isolated from hearts of transgenic animals showed frequency-dependent reduced percent shortening and decreased rates of contraction and relaxation compared with control animals. Cardiomyocytes isolated from transgenic animals had lower basal levels of intracellular free Ca2+ and a reduced rise in free Ca2+ following depolarization. After stimulation, intracellular free Ca2+ returned to basal levels faster in transgenic cells than in cells from control animals. These data demonstrate that the overexpression of annexin VI in the heart disrupts normal Ca2+ homeostasis and suggests that this dysfunction may be due to annexin VI regulation of pumps and/or exchangers in the membranes of cardiomyocytes.

Modeling of mechanical dysfunction in regional stunned myocardium of the left ventricle

Reversible mechanical dysfunction of the myocardium after a single or multiple episode(s) of coronary artery occlusion has been observed in previous studies and is termed myocardial stunning. The hypothesis that stunning could be represented by a decrease in maximum available muscle force in the stunned region was examined by means of a mathematical model that incorporates series viscoelastic elements. A canine experimental model was also employed to demonstrate depressed contractility and a consistent delay of shortening in the stunned region. The mechanical model of the left ventricle was designed to include a normal and stunned region, for which the stunned region was allowed to have variable size. Each region consisted of a volume and time dependent force generator in parallel with a passive elastic force element. The passive elastic element was placed in series with a constant viscosity component and a series elastic component. The model was solved by means of a computer. Passive and active properties of each region could be altered independently. The typical regional measures of muscle performance such as percent shortening, percent bulge, percent thickening, delay of shortening, percent increase in end-diastolic length and other hemodynamic measures were computed. These results were similar to those observed in animal models of stunning. In addition, a nearly linear relationship with end-diastolic length and delay of shortening was predicted by the model. It was concluded that a decrease in the peak isovolumic elastance and augmentation of viscosity effect of creep during stunning can explain mechanical abnormalities of stunned myocardium.

Biophysical aspects of meat tenderness

Biophysical aspects of meat tenderness is reviewed, where the meat structural origin of variation in meat tenderness is tried to be elucidated. Processes, such as rigor development and ageing, known to influence the properties of the structural components, is covered, and variables that influence those processes, such as chilling, electrical stimulation and stress ante-mortem, are discussed. Meat tenderness can be evaluated both by sensory and instrumental methods. The relationships between mechanical and sensory assessments tend to be non-linear, which can be due to non-linearity in the sensory evaluation and that muscle fibre orientation is easier to control in instrumental than in sensory evaluation. Structural changes of the meat occuring during rigor development are both longitudinal and lateral contraction of the myofibrillar mass. Other structural events, based on the proteolytic action, are the loosing up of the myofibrils held together laterally, weakening of the myofibrillar length and myofibril fragmentation. Using instrumental recordings of meat toughness (Warner-Bratzler (W-B) peak force), it decreases significantly with degree of contraction, when raw, but the reverse is found, when meat is cooked above 60 °C. A structural explanation to this behaviour is suggested to be the following. When meat is raw the lateral contraction of the meat fiber increases with shorter sarcomeres, giving rise to a larger viscous component and hence a lower W-B peak force. On heating, however, with a larger extracellular space, when shortened, there is more room for the connective tissue to contract without being restricted by the myofibrillar mass. This in turn gives a higher number of fibers per unit cross-sectional area, hence a larger elastic modulus and a higher W-B peak force, when cooked. When chilling of muscle during rigor both warm- and cold-shortening occur. Minimal shortening region is for beef M. longissimus dorsi (LD) 10–15 °C and for M. semimembranosus (SM) 7–13 °C. For the SM muscle there is a high correlation between percentage shortening and ultimate tenderness both in the warm- and cold-shortening region. But for the LD muscle this is only the case in the cold-shortening region. This observation suggests that the LD muscle is a more enzymatically active muscle than SM. The influence of low-voltage electrical stimulation (ES) was followed in the cold-shortening region for muscles LD and SM. A significant effect on tenderness 15 days post-mortem was only observed for LD at 1 °C and 4 °C, but not for SM. It was suggested that enhanced proteolysis could be the reason for the improved tenderness on ES of LD, as colds-hortening was not prevented by ES. Long-term and short-term stress ante-mortem can give rise to DFD (dark, firm and dry)-and PSE (pale, soft and exudative)-meat, respectively. DFD-meat (pH u > 6.0 in LD) has relatively short sarcomere lengths, but still it is swollen laterally and has consequently a small extracellular space. Therefore DFD-meat usually is tender. PSE-meat has a large variation in sarcomere length. The long sarcomeres of PSE-meat is suggested to be caused by reduced shortening, due to the denaturation of the sarcoplasmic proteins during rigor. The short sarcomeres can be caused by a higher percentage of rigor development in the warm-shortening region and that the denaturation of the myosin heads cause both longitudinal and lateral contraction of the myofibrillar mass. There is also a large variation in tenderness of PSE-meat, but it has been found that this variation is positively correlated to the sarcomere length (r = 0.52**), as has been shown for the other variables that governs the rigor process.

Regional effects of aortomyoplasty in acute ischemia

Aortomyoplasty is a technique for achieving autogenous diastolic counterpulsation. This experiment was designed to determine if aortomyoplasty using conditioned latissimus dorsi muscle could improve regional myocardial function during coronary ischemia. Six mongrel dogs underwent a staged operation in which the left latissimus dorsi was conditioned in situ for 4 weeks, then wrapped around the descending aorta and stimulated during diastole with each cardiac contraction. Regional ischemia was caused by occlusion of the left anterior descending coronary artery. Regional function was measured with somomicrometry in the region of ischemia and in a control area. An intraaortic balloon pump was inserted for comparison with aortomyoplasty performance. Coronary artery occlusion caused a significant decrease in the percentage of regional shortening (14.2 +/- 7.9 to -2.2 +/- 4.0; p = 0.001) and thickening (11.9 +/- 4.6 to -5.8 +/- 3.3; p < 0.001). Aortomyoplasty improved regional motion in both percentage shortening (-2.2 +/- 4.0 to 2.3 +/- 3.7; p = 0.008) and thickening (-5.8 +/- 3.3 to 2.8 +/- 1.9; p < 0.001). The intraaortic balloon pump also improved percentage shortening (-3.7 +/- 2.0 to 0.7 +/- 1.9; p = 0.01) and thickening (-5.0 +/- 2.8 to 2.4 +/- 3.8; p < 0.001), and was not significantly different than aortomyoplasty. These data show that aortomyoplasty has beneficial effects on ischemic left ventricular contractility, and may therefore be useful for treating inoperable coronary artery disease.

Regional alterations of left ventricular contraction and inotropic reserve in conscious dogs with heart failure

The goal was to examine left ventricular (LV) regional contraction alterations and especially, regional inotropic reserve changes in tachycardia-induced heart failure (HF). Eleven dogs were chronically instrumented to measure LV pressure and its first time derivative (LV dP/dt), left atrial and aortic pressures and to measure antero-apical (AS), -basal (BS) and postero-apical (PS) subendocardial segmental contractions by ultrasonic crystals. Dobutamine (5-15 micrograms/kg per min) and left atrial pacing (150-240 beats/min) were performed in the control state (C) and in HF induced by chronic right ventricular pacing (240 beats/min, 3 weeks). In HF, as compared with in C, LV dP/dt max decreased and LV end-diastolic pressure and end-diastolic segmental lengths increased (Ps < 0.005). The percentage of systolic shortening was more depressed in PS (from 21 +/- 1% to 7 +/- 1%, P < 0.001) than in AS and BS (from 24 +/- 1% to 17 +/- 1% and from 20 +/- 2% to 13 +/- 1% respectively, Ps < 0.05). During dobutamine infusion, in HF as compared with C, the increases in LV dP/dt max were smaller (dobutamine 15 micrograms/kg per min: HF: + 36 +/- 6% vs C: + 68 +/- 11%, P < 0.01) and the increases in the systolic shortening of the three segments were also smaller. However, the responses of the three segments were similar in HF and in C. During left atrial pacing, LV dP/dt max increased less in HF than in C and the poststimulation potentiation of LV dP/dt max was impaired in HF. However, the responses of the systolic shortening during regular left atrial pacing and the increase in the percentage of systolic shortening of the first poststimulation beat were similar in all regions. In tachycardia-induced HF, although LV regional contraction is heterogeneously altered, the inotropic reserve appears to be similarly modified in all regions.

Direct Effects of Protamine Sulfate on Myocyte Contractile Processes

Administration of the arginine-rich, highly charged protamine (PROT) molecule has been associated with episodes of acute left ventricular (LV) dysfunction. The objective of the present study was to test the hypothesis that PROT has direct effects on isolated LV myocyte contractile processes and sarcolemmal transduction systems. Exposure of porcine LV myocytes (n = 305) to 40 micrograms/mL PROT (reflecting a dose of 2.5 mg/kg) decreased basal contractile function and beta-adrenergic responsiveness. For example, myocyte percent shortening was 4.3 +/- 0.1% in control myocytes and decreased to 2.8 +/- 0.2% in the presence of 40 micrograms/mL PROT (P < .05). Myocyte percent shortening was 9.3 +/- 0.7% after beta-adrenergic receptor stimulation (isoproterenol; 25 nmol/L) and was significantly reduced in the presence of 40 micrograms/mL PROT (5.7 +/- 0.7%, P < .05). PROT reduced myocyte responsiveness to forskolin (100 mumol/L), which directly activates adenylate cyclase, by > 40% from forskolin. In addition, PROT abolished the inotropic effects of ouabain on myocyte contractile function. To determine contributory mechanisms for the effects of PROT on myocyte sarcolemmal systems, beta-receptor- and cardiac glycoside-binding characteristics were determined in sarcolemmal preparations. beta-receptor binding was 175 +/- 10 fmol/mg and was reduced to 140 +/- 6 fmol/mg in the presence of PROT (P < .05). Ouabain receptor binding was 7.1 pmol/mg and decreased to 2.6 +/- 0.4 pmol/mg in the presence of PROT. In addition, cAMP production after stimulation with isoproterenol and forskolin was significantly blunted in the presence of PROT. Variants of the PROT moelcule were constructed by specific amino acid substitutions and deletions, which provided a means to vary charge as well as structure. Substitution of arginine with lysine in the PROT peptide sequence ameliorated the negative effects on myocyte contractile processes; despite identical overall charge (21+). However, a PROT variant with an 18+ charge but different amino acid sequence induced significant negative effects on myocyte function and inotropic responsiveness. Thus, the effects of PROT on myocyte contractile processes are not due simply to the high positive charge of the molecule. To further establish that PROT can contribute to changes in LV function in the clinical setting, fluorescein-labeled PROT was circulated in antegradely perfused rabbit hearts. Microscopic examination revealed that PROT could traverse the vascular compartment of the myocardium and come in direct contact with the myocyte. The unique findings from the present study suggest that a fundamental contributory mechanisms for the changes in LV function observed after protamine administration may be the direct effect of unbound protamine on myocyte contractile processes.

Volume change accompanying cleavage development in graptolitic shales from Gisborne, Victoria, Australia

Studies on shape changes in deformed Oncograptus upsilon combined with strain analysis of pressure shadows around framboidal pyrite revealed that a small volume change of the order of 5 percent accompanied the cleavage development in the shales from Gisborne, Victoria. Starting from the proximal end, Oncograptus upsilon exhibits progressive increase in the spacing between successive thecae along the stipes. A new technique utilizing the distance between a specific number of thecae is used for computing the change in length along stipes of Oncograptus upsilon. The low volume change, accompanying a more than 70 percent shortening deformation, indicates that there is a less significant mass loss during cleavage development than has been inferred from some studies on volume change from thecal spacing in deformed graptolites.

Decreased contractile responses to isoproterenol in isolated cardiac myocytes from ageing guinea-pigs

We have characterized the age-related changes of contractility and β-adrenoceptor function in isolated cardiac myocytes from guinea-pigs. We used either adult animals from 2 to 14 weeks of age, where body weight increases linearly with age, or senescent ones aged between 53–65 weeks. There was some indication of a decrease in contractility in maximum Ca 2+ with age, with significant differences between a young (≤4 weeks, weight <400 g) and aged (≥8 weeks, weight >600 g) group in contraction amplitude expressed as percentage shortening (but not when expressed as μm change in length) or contraction and relaxation velocities. This decline was continued into senescence, and ANOVA showed a significant difference between the three groups for contraction amplitude (percentage shortening, 12.2 ± 0.9%, young, n = 31; 9.5 ± 0.6%, n = 28 aged; 6.7 ± 0.8%, n = 6, senescent; P = 0.005), and contraction or relaxation velocities ( P<0.001). There was a more pronounced decline in maximum response to isoproterenol with age. ANOVA for the maximum isoproterenol response for the three divisions showed significant differences for percentage shortening (11.8 ± 0.7%, n = 30, young; 7.9 ± 0.5%, n-28, aged and 5.5 ± 1.1%, n = 6, senescent; P<0.001), velocities of contraction ( P<0.001) and relaxation ( P<0.001), and normalized velocities of contraction ( P<0.001) and relaxation ( P<0.01) at maximum isoproterenol, as well as in ISO EC 50 ( P<0.001) and isoproterenol/Ca 2+ ratio ( P<0.02). A general decrease in contractility of the myocyte occurs as the animal ages, with maximum contraction amplitude being reduced and velocity of contraction and relaxation slowed. The effect was more pronounced for β-adrenoceptor stimulation than for high Ca 2+, suggesting a specific lesion in the adenylate cyclase related pathway. Much of the change occurred between the young adult (≤4 weeks) and the aged adult (≥8 weeks), although the trend was continued in senescent animals (>52 weeks).

997-90 Right (RV) and Left Ventricular (LV) Geometry and Myocyte Contractile Processes with Dilated Cardiomyopathy (DCM): Disparity Between Myocyte Growth and β-Adrenergic Responsiveness

The progression of DCM has been assumed to be a homogenous process for both the RV and LV. However, this assumption has never been tested. Accordingly, we measured myocyte contractile performance (velocity of shortening, VELSHORT; percent shortening, PERSHORT) at baseline (BASE) and after β -adrenergic receptor stimulation ( β AR, 25 nM isoproterenol) of isolated myocytes taken from the RV and LV of 5 pigs with pacing induced DCM (240 bpm, 3 weeks) and 5 control pigs (CON). RV and LV mass/body weight (MASS) and myocyte length and cross-sectional area (CSA) were also determined. CON-RV CON-LV DCM-RV DCM-LV VELSHORT-BASE ( μ m/s) 90 ± 5 + 50 ± 1 48 ± 2 * , + 32 ± 1 * VELSHORT- β AR ( μ m/s) 206 ± 8 + 150 ± 5 123 ± 8 * 111 ± 9 * PERSHORT-BASE (%) 5.8 ± 0.2 + 4.6 ± 0.1 3.1 ± 0.1 * , + 2.2 ± 0.1 * PERSHORT- β AR (%) 11.5 ± 0.3 + 10.2 ± 0.3 59 ± 0.3 * 5.2 ± 0.4 * Length ( μ m) 150 ± 2 + 137 ± 1 179 ± 2 * , + 173 ± 2 * CSA ( μ m 2 ) 176 ± 4 + 362 ± 8 232 ± 4 * , + 292 ± 5 * Mass (gm/kg) 0.8 ± 0.1 + 2.8 ± 0.1 1.6 ± 0.1 * , + 2.9 ± 0.2 + p &lt; 0.05 vs LV * p &lt; 005 vS CON In controls, RV myocytes were longer and had a smaller CSA, but enhanced contractile performance at baseline and with β -adrenergic stimulation. With DCM, no LV hypertrophy occurred. In contrast, RV chamber and cellular hypertrophy occurred and was associated with a persistent increase of RV myocyte baseline contractile function. This study demonstrated, for the first time, that differences in RV and LV myocyte function and β -adrenergic responsiveness exist in normal and DCM states. More importantly, a disparity in RV and LV myocyte growth with DCM occurred. Thus, in this model of DCM, RV and LV growth and changes in contractile performance are not a homogenous process, and suggest that inherent differences exist in the response of RV and LV myocytes to stress.