Percent Shortening Research Articles

Macrophage migration inhibitory factor is a cardiac-derived myocardial depressant factor.

Macrophage migration inhibitory factor (MIF) is a pluripotent proinflammatory cytokine that is ubiquitously expressed in organs, including the heart. However, no specific role for MIF in modulating cardiac performance has yet been described. Therefore, we examined cardiac MIF expression in mice after LPS challenge (4 mg/kg) and tested the hypothesis that MIF is a mediator of LPS-induced cardiac dysfunction. Western blots of whole heart lysates, as well as immunohistochemistry, documented constitutive MIF protein expression in the heart. Cardiac MIF protein levels significantly decreased after LPS challenge, reaching a nadir at 12 h, and then returned to baseline by 24 h. This pattern was consistent with MIF release from cytoplasmic stores after endotoxin challenge. After release of protein, MIF mRNA levels increased 24-48 h postchallenge. To determine the functional consequences of MIF release, we treated LPS-challenged mice with anti-MIF neutralizing antibodies or isotype control antibodies. Anti-MIF-treated animals had significantly improved cardiac function, as evidenced by a significant improvement in left ventricular (LV) fractional shortening percentage at 8, 12, 24, and 48 h after endotoxin challenge. In support of these findings, perfusion of isolated beating mouse hearts (Langendorff preparation) with recombinant MIF (20 ng/ml) led to a significant decrease in both systolic and diastolic performance [LV pressure (LVP), positive and negative first derivative of LVP with respect to time, and rate of LVP rise at developed pressure of 40 mmHg]. This study demonstrates that MIF mediates LPS-induced cardiac dysfunction and suggests that MIF should be considered a pharmacological target for the treatment of cardiac dysfunction in sepsis and potentially other cardiac diseases.

Effects of triiodothyronine pretreatment on beta-adrenergic responses in stunned cardiac myocytes

Objective: To investigate whether triiodothyronine pretreatment enhanced beta-adrenergic responses in stunned myocardium and whether this acute effect of triiodothyronine was mediated through the cyclic adenosine 3′,5′-monophosphate (AMP) system. Design: A prospective study. Setting: University laboratory. Participants: Rabbits. Interventions: Rabbit ventricular myocytes were isolated and placed in a medium equilibrated with either air (control) or with 95% N 2 and 5% CO 2 (stunned) for 15 minutes at 37°C. The stunned myocytes were reoxygenated with air for 30 minutes. Triiodothyronine (10 nmol/L) and/or isoproterenol (0.1 nmol/L) was added to the myocytes. Myocyte shortening was measured by using a video-edge detector. Measurements and Main Results: In electrically stimulated cells, the basal values of the percent shortening (22%-30%) and the maximum rate of shortening (22%-25%) were significantly reduced in the stunned myocytes. Isoproterenol (5 minutes) alone significantly increased the percent shortening in the control (from 3.70 ± 0.36 to 4.14 ± 0.37) but not in the stunned myocytes (from 2.60 ± 0.30 to 3.15 ± 0.27). Triiodothyronine (5 minutes) alone significantly increased the percent shortening in the control (from 3.75 ± 0.36 to 4.34 ± 0.45) and in the stunned myocytes (from 2.91 ± 0.2 to 3.85 ± 0.26). After triiodothyronine pretreatment for 5 minutes, isoproterenol caused greater increases in the percent shortening in both the control (37%) and the stunned myocytes (62%) than either agent alone. Isoproterenol or triiodothyronine caused small increases in the maximum rate of shortening in the control (14%-16%) and the stunned myocytes (34%-49%). After triiodothyronine pretreatment, isoproterenol caused greater increases in the maximum rate of shortening in both groups (control: 41%, stunned: 73%) than either agent alone. Isoproterenol caused an increase in the level of cyclic AMP (ρ;moles/10 5 myocytes) in the control (from 2.92 ± 0.47 to 3.77 ± 0.43) but not in the stunned myocytes (from 2.42 ± 0.25 to 2.42 ± 0.20). Triiodothyronine pretreatment did not cause any change in cyclic AMP levels in the control (2.50 ± 0.29) or in the stunned myocytes (2.60 ± 0.40). After triiodothyronine pretreatment, isoproterenol caused a small increase in the cyclic AMP level in the control but not in the stunned myocytes. Conclusions: The data showed that the myocardial beta-adrenergic responses were more sensitive to ischemic insult than the triiodothyronine responses. Triiodothyronine pretreatment enhanced beta-adrenergic responses in both the control and the stunned myocytes. However, this acute positive inotropic effect of triiodothyronine might not be mediated through the cyclic AMP system.

Alterations in nitric oxide-cGMP pathway in ventricular myocytes from obese leptin-deficient mice.

Leptin is a regulator of body weight and affects nitric oxide (NO) production. This study was designed to determine whether the myocardial NO-cGMP signal transduction system was altered in leptin-deficient obese mice. Contractile function, guanylyl cyclase activity, and cGMP-dependent protein phosphorylation were assessed in ventricular myocytes isolated from genetically obese (B6.V-Lepob) and age-matched lean (C57BL/6J) mice. There were no differences in baseline contraction between the lean and obese groups. After stimulation with the NO donor S-nitroso-N-acetyl-penicillamine (SNAP, 10-6 and 10-5 M) or a membrane-permeable cGMP analog 8-bromo-cGMP (8-Br-cGMP, 10(-6) and 10(-5) M), cell contractility was depressed. However, 8-Br-cGMP had significantly greater effects in obese mice than in lean controls with percent shortening reduced by 47 vs. 39% and maximal rate of shortening decreased by 46 vs. 36%. The negative effects of SNAP were similar between the two groups. Soluble guanylyl cyclase activity was not attenuated. This suggests that the activity of the cGMP-independent NO pathway may be enhanced in obesity. The phosphorylated protein profile of cGMP-dependent protein kinase showed that four proteins were more intensively phosphorylated in obese mice, which suggests an explanation for the enhanced effect of cGMP. These results indicate that the NO-cGMP signaling pathway was significantly altered in ventricular myocytes from the leptin-deficient obese mouse model.

Adding angiotensin II type 1 receptor blockade to angiotensin-converting enzyme inhibition limits myocyte remodeling after myocardial infarction

Background: Adding angiotensin II type 1 receptor blockade (ARB) to angiotensin-converting enzyme inhibition (ACEI) further attenuates left ventricular (LV) remodeling in an ovine model of myocardial infarction (MI). We hypothesized that combined therapy with ACEI and ARB (CT) would be additive in the limitation of the myocyte hypertrophy and dysfunction that occurs in untreated adjacent noninfarcted regions during remodeling. Methods and Results: Nineteen sheep underwent coronary ligation to create a moderate-sized anteroapical infarction. Post-MI day 2, sheep were randomized to therapy with ramipril (ACEI, n = 5) or ramipril plus losartan (CT, n = 6) or none (untreated, n = 8). Infarct size was similar between groups. At 8 weeks post-MI, myocytes were isolated from regions adjacent to and remote from the infarct to measure morphometric indices (cell volume, length, cross-sectional area, width) and parameters of contraction (% shortening and −dL/dt, rate of shortening) and relaxation (+dL/dt [rate of relengthening] and TR 70% [time for 70% relengthening]). Volume % collagen was measured from adjacent and remote regions. Adjacent myocyte volume was different between groups (2.5 ± 0.1 × 104 μm3 in CT, 3.0 ± 0.4 × 104 μm3 in ACEI, 3.5 ± 0.2 × 104 μm3 in untreated, analysis of variance [ANOVA] P =.001) as was length (158 ± 4 μm, 161 ± 9 μm, 189 ± 8 μm, respectively, ANOVA P <.001). Adjacent cell volume and length in CT were lower than untreated (P <.05). Percent shortening and −dL/dt of isolated adjacent myocytes were improved with both ACEI (7.9 ± 0.3%, −131 ± 6 μm/sec, P <.05) and CT (7.7 ± 0.3%, −144 ± 8 μm/sec, P <.05) compared with no therapy (6.4 ± 0.4%, −104 ± 7 μm/sec), as was both +dL/dt and TR 70%. No between-group difference in volume % collagen was found in adjacent or remote regions. Conclusion: Compared with ACEI alone, the addition of ARB further limits adjacent noninfarcted myocyte hypertrophy during post-MI LV remodeling. Both ACEI alone and CT preserve isolated unloaded myocyte function, but neither significantly reduce interstitial collagen. The additional benefit of ARB on regional and global function in vivo may also be due to other factors including regional load.

Ethanol Reduces Cardiac Myocyte Function through Activation of the Nitric Oxide-Cyclic GMP Pathway

We tested the hypothesis that low-dose ethanol would reduce cardiac myocyte function through increased production in the nitric oxide/cyclic GMP signal transduction pathway, rather than reduced degradation. Ventricular myocytes were isolated from the hearts of 9 rabbits. Myocyte function was studied using a video-edge detector and cyclic GMP levels were measured by radioimmunoassay. Cells were administered 5 and 10 mmol/l ethanol alone or after 10^–6 mol/l N^G-nitro-L-arginine methyl ester (L-NAME, nitric oxide synthase inhibitor), 10^–6 mol/l 1H-[1,2,4]oxadiazolo[4,3a]quinoxalin-1-one (ODQ, soluble guanylyl cyclase inhibitor) or 10^–5 mol/l zaprinast (cyclic GMP phosphodiesterase inhibitor). Ethanol (10 mmol/l) significantly decreased percent shortening from 10.0 ± 0.9 to 6.0 ± 0.2%. Similar decrements occurred in the maximum rate of shortening and relaxation. After L-NAME or ODQ, the decrements in percent shortening, maximum rate of shortening and relaxation caused by ethanol were not significant. After zaprinast, ethanol significantly decreased the maximum rate of shortening and relaxation and percent shortening to 4.3 ± 0.5. Ethanol (10 mmol/l) significantly increased cyclic GMP from 403 ± 121 to 529 ± 128 fmol/10⁵ myocytes. Both L-NAME and ODQ lowered cyclic GMP, and ethanol did not affect cyclic GMP after either. Zaprinast raised cyclic GMP, as did its combination with 10 mmol/l ethanol (653 ± 120). Thus, ethanol both reduced myocyte function and increased cyclic GMP. Blocking nitric oxide production or guanylyl cyclase activity prevent these effects of ethanol, while blocking cyclic GMP degradation did not. This suggests that ethanol acts as a nitric oxide stimulator in ventricular myocytes leading to reduced function and increased cyclic GMP.

Decoy calcium channel beta subunits modulate contractile function in myocytes.

To test the hypothesis that mutated beta2-subunits of the L-type calcium channel could serve as a decoy and interdict calcium channel trafficking and function, we engineered a beta2 subunit that contained the beta interaction domain for alpha1c subunit interaction, but lacked N- and C-terminal domains that might be essential for sarcolemmal localization. An adenoviral vector was constructed containing the gene for the beta-interaction domain (BID) fused to green fluorescence protein (GFP), using a vector containing only GFP as control. Freshly plated, dissociated adult rat myocytes were infected and expression and function were assessed at 60 h. Fluorescence microscopy confirmed GFP expression; immunoblot analysis confirmed dose-dependent GFP-BID expression. Mechanical properties of adult rat ventricular myocytes were evaluated using a video edge-detection system. Contractility analysis (optical/video, field stimulation) demonstrated that contracting cells decreased from 60 to 2%. Contractile amplitude (percent shortening) decreases significantly from 5.6 vs. 2.4% with no change in time to peak twitch. Recombinant adenovirus overexpressing mutated beta2 subunits in adult mammalian myocytes can markedly alter excitation-contraction coupling. This paradigm may offer new approaches to understanding and modulating EC coupling.

Accommodation of late Cenozoic oblique shortening in the Alborz range, northern Iran

The Alborz range, northern Iran, deforms by strain partitioning of oblique shortening onto range-parallel left-lateral strike-slip and thrust faults. Deformation is due to the north–south Arabia–Eurasia convergence, and westward motion of the adjacent South Caspian relative to Iran. Roughly north–south shortening occurs on thrusts that dip inwards from the range margins. Precambrian basement is not exposed because of detachment along upper Proterozoic evaporites and the thickness of overlying strata (∼10 km). Other detachments occur within Phanerozoic sediments. Active left-lateral strike-slip faults trend ENE in the east of the range, WNW in the west. The eastern Mosha Fault has a left-lateral offset of ∼30–35 km. Shortening across the range is ∼30 km (25–30%) at the longitude of Tehran. This is hard to reconcile with the crustal thickness of ∼35 km, which is similar to adjacent basins. Percentage shortening across the Alborz is similar to the adjacent Kopet Dagh, but because the latter is twice as wide, finite shortening is roughly half. The difference may be accommodated by subduction of the adjacent South Caspian Basin northwards under the middle Caspian. South Caspian sediments began folding in the Pliocene; the present kinematics of the Alborz may have begun at this time, including a reversal from range-parallel right-lateral to left-lateral strike-slip faulting, but the regional stratigraphy indicates uplift as early as the mid Tertiary.

Initial experience with intratherapeutics Intrastent Doublestrut LD stents in patients with congenital heart defects.

Limitations of the currently available balloon-expandable stainless steel (BE-SS) stents for use in patients with congenital heart defects (CHD) include inflexibility, significant shortening with expansion, sharp ends, and limited sizes. These limitations increase risk and greatly effect success of stent placement in these patients. The recently approved IntraStent DoubleStrut LD (IS-LD) stents are BE-SS stents designed to address such limitations. We report our initial experience with IS-LD stents in patients with CHD. Using standard techniques, 36 stents were implanted in 22 patients whose median age was 11 years (range, 1.4-35 years) and weight was 33 kg (range, 9-96.8 kg). Lesions stented included aortic coarctation (4), branch pulmonary arteries (19), inferior or superior vena cava (11), Mustard baffle (1), and Fontan baffle (1). All attempts at stent placement were successful. Hemodynamic assessment and angiography was performed pre- and poststent placement in all patients. Intravascular ultrasound was performed in four patients. Stenosis diameter increased from 5.7 +/- 0.6 mm (mean +/- SD) to 11.6 +/- 0.5 mm (P < 0.001). Stents did not shorten significantly with dilation (median percent shortening, 3.8%; P > 0.1). Complications included stent recoil (2), stent migration (1), and stent distortion (1). IS-LD stents are a safe and effective treatment for the majority of vascular stenoses in patients with CHD. Stent recoil at large diameters may limit its usefulness in selected lesions. Follow-up studies are required to determine the long-term performance of IS-LD stents.

Preconditioning attenuates the shortening of recovery during coronary occlusion in isolated rabbit hearts with D-sotalol-induced long QT intervals.

The effects of 20-min ligations of the anterior branch of the left coronary artery were studied in Langendorff-perfused rabbit hearts with 92 microM D-sotalol added to the perfusate to induce long QT intervals and triggered arrhythmias. Epicardial electrograms, a left ventricular endocardial monophasic action potential, and simulated X and Y lead electrocardiograms were used to characterize ventricular conduction and recovery. In contrast to previous work showing that global ischemia eliminated triggered activity, coronary occlusion did not alter its mean incidence. Although the anatomic distribution of earliest sites of epicardial activation by triggered beats was altered, triggered beats still appeared on the epicardial surface in the nonperfused regions. Coronary occlusion had a small and variable effect on epicardial conduction velocity but caused a significantly greater percent shortening of epicardial activation-recovery intervals in the nonperfused region of hearts given D-sotalol than in control hearts. In hearts given D-sotalol, preconditioning significantly attenuated the shortening of epicardial activation-recovery intervals in response to coronary occlusion. However, preconditioning had no effect on the mean incidence of triggered activity during coronary occlusion. Thus, the persistence of triggered activity and the shortened myocardial recovery time associated with coronary occlusion could contribute to increasing the likelihood of occurrence of malignant ventricular arrhythmias. Preconditioning by attenuating the shortening of recovery would be anti-arrhythmic.

Bone marrow-derived regenerated cardiomyocytes (CMG Cells) express functional adrenergic and muscarinic receptors.

We recently reported that cardiomyocytes could be differentiated from bone marrow mesenchymal stem cells in vitro by 5-azacytidine treatment. In native cardiomyocytes, adrenergic and muscarinic receptors play crucial roles in mediating heart rate, conduction velocity, contractility, and cardiac hypertrophy. We investigated whether these receptors are expressed in differentiated CMG cells, and if so, whether they have downstream signaling systems. Reverse transcription-polymerase chain reaction revealed that CMG cells had already expressed alpha(1A)-, alpha(1B)-, and alpha(1D)-adrenergic receptor mRNA before 5-azacytidine treatment, whereas expression of beta(1)-, beta(2)-adrenergic and M(1)-, M(2)-muscarinic receptors was first detected at 1 day. Phenylephrine dose-dependently induced phosphorylation of ERK1/2, which was completely inhibited by prazosin, and significantly increased cell size. Isoproterenol augmented cAMP by 38-fold, which was fully inhibited by propranolol. Isoproterenol (10(-7) mol/L) increased the spontaneous beating rate by 47.6% (basal, 127+/-16 bpm), and propranolol and CGP20712A (beta(1)-selective blocker) reduced it by 79.0% and 71.0%, respectively, whereas ICI118551 (beta(2)-selective blocker) induced slight reduction. Cell motion, percent shortening, and contractile velocity were increased by 37.5%, 26.9%, and 50.6%, respectively, in response to isoproterenol. Phenylephrine and isoproterenol augmented ANP and BNP gene expressions. Carbachol increased IP(3) by 32-fold, which was markedly inhibited by atropine as well as AFDX116 (M(2)-selective blocker) measured by radioimmunoassay. These findings indicate that CMG cells expressed alpha(1A), alpha(1B), and alpha(1D) receptors before differentiation and expressed beta(1), beta(2), M(1), and M(2) receptors after they obtained the cardiomyocyte phenotype. These receptors had functional signal transduction pathways and could modulate cell function.

Cyclic GMP-Induced Reduction in Cardiac Myocyte Function Is Partially Mediated by Activation of the Sarcoplasmic Reticulum Ca2+-ATPase

We tested the hypothesis that the mechanism through which cyclic GMP reduces cardiac function is mediated by activation of the sarcoplasmic reticulum Ca²⁺-ATPase (SERCA). Cardiac myocytes were isolated from New Zealand white rabbits (n = 11). Individual ventricular cells were stimulated by electrical field stimulation. The maximal rate of cell shortening and percentage shortening were measured with a video edge detector. Thapsigargin (10^–8 mol/l) was used as a specific inhibitor of SERCA. When 8-bromo-cyclic GMP (8-Br-cGMP, 10^{–7, –6, –5} mol/l) was added to cells, the maximal rate of myocyte shortening (R_max, µm/s) and percentage shortening were both decreased in a concentration-dependent manner. R_max decreased 27% from 117 ± 12 at baseline to 85.2 ± 13 when 10^–5 mol/l of 8-Br-cGMP was present, and percent shortening was reduced 28% from 6.0 ± 0.5 to 4.3 ± 0.5%. Thapsigargin (10^–8 mol/l) increased the maximal rate of myocyte shortening and percent shortening. Addition of thapsigargin prior to 8-Br-cGMP reduced the negative effects of cGMP on myocyte function. The percent shortening decreased only 11% and R_max decreased 14% with 10^–5 mol/l 8-Br-cGMP, which was not significant. Cyclopiazonic acid, another SERCA inhibitor, was also used to test whether 8-Br-cGMP reduced myocyte function through SERCA. The results were similar to those when thapsigargin was used. These results indicated that the cyclic GMP-induced reduction in cardiac myocyte function was partially mediated through the action of the sarcoplasmic reticulum Ca²⁺-ATPase.

Right ventricular ejection function assessed by cineangiography--Importance of bellows action.

The right ventricular ejection fraction (RVEF) can be shown theoretically as a mathematical function of the percent shortening in the 3 axial dimensions of the right ventricular cavity (the septum-free wall dimension (SF), the anterior-posterior dimension (AP), and the tricuspid valve-apex dimension (TA) or the long axis dimension (LA)). There is a need to decide which mechanism is the most important for the RVEF in cases with neither obvious regional wall motion abnormalities of the left ventricle nor right ventricular overload. Forty-four consecutive subjects (34 males/10 females) were enrolled: 16 had normal hemodynamic parameters without significant coronary artery stenosis, 15 had hypertrophic cardiomyopathy and 13 had dilated cardiomyopathy. Biplane right ventricular cineangiography was performed and the percent shortening of the SF, AP, and TA or LA were measured. The percent shortening in the SF (34.8+/-14.7%) was larger than that of the AP, TA, and LA (23.2+/-8.5, 21.0+/-8.3 and 18.3+/-7.0, respectively; all p<0.001). There was a linear correlation between the percent shortening of each dimension and the RVEF. The 95% confidence interval of the regression equation from the percent shortening of the SF and RVEF was located above those from the other percent shortenings, except for a lower RVEF. These results indicate that systolic shortening of the SF (ie, bellows action) plays an important role in the RVEF except for a lower ejection fraction.

Vibrational and thermal study on the in vitro and in vivo degradation of a bioabsorbable periodontal membrane: Vicryl Periodontal Mesh (Polyglactin 910).

Fourier transform Raman (FT-Raman), attenuated total reflection/Fourier transform infrared (ATR/FT-IR) spectra and differential scanning calorimetry (DSC) measurements were performed on a biodegradable periodontal membrane, the Vicryl periodontal mesh, in order to study its in vitro and in vivo degradation mechanism and kinetics. The hydrolitic in vitro degradation was investigated in two aqueous media: a saline phosphate buffer (SPB, pH=7.4) and a 0.01 M NaOH solution. Moreover, a membrane implanted in vivo for 4 weeks for treatment of contiguous vertical bony defects, was examined. Vibrational and thermal measurements show that the Vicryl membrane presents a semicrystalline structure. It degrades faster in the NaOH solution than in the SPB and degradation occurs heterogeneously with a progressive increase in the percentage of crystallinity and shortening of the polymeric chains both in vitro and in vivo. The trends of % weight loss and IR I627/I1415 intensity ratio (identified as a marker of crystallinity) are discussed in comparison with the DSC results. The IR I627/I1415 intensity ratio and Xc% allow to determine the % weight loss undergone by the membrane degraded in vivo. The result obtained shows that the Vicryl membrane degrades faster in vivo than in vitro with the formation of oligomers which are more easily absorbed by the surrounding tissues than they are soluble in the degradation media examined.

Nitric oxide and cGMP protein kinase activity in aged ventricular myocytes.

We tested the hypothesis that nitric oxide-induced negative functional effects through cGMP would be reduced in aged cardiac myocytes. Maximum rate of shortening (R(max)) and percent shortening of ventricular myocytes from young (6 mo) and old (3 y) rabbits were studied using a video edge detector. cGMP-dependent phosphorylation was examined by electrophoresis and autoradiography. Myocytes received a nitric oxide donor S-nitroso-N-acetyl-penicillamine (SNAP, 10(-7), 10(-6), and 10(-5) M) followed by KT-5823 (10(-6) M), a cGMP protein kinase inhibitor. Baseline function was similar in young and old myocytes (89.1 +/- 4.5 young vs. 86.4 +/- 8.3 microm/s old R(max), 5.6 +/- 0.3 vs. 5.2 +/- 0.7%shortening). SNAP (10(-5) M) decreased R(max) in both young (25%, n = 6) and old myocytes (24%, n = 7). SNAP also reduced percent shortening by 28% in young and 23% in old myocytes. The negative effects of SNAP were partially reversed by KT-5823 only in young myocytes. Multiple proteins were phosphorylated by cGMP, and KT-5823 could reduce this effect. The degree of phosphorylation was significantly less in old myocytes. These results suggest that the functional response of ventricular myocytes to nitric oxide was preserved during aging. However, the importance of cGMP-dependent protein phosphorylation was decreased, indicating a shift to other pathways.

Echocardiographic changes in the development of the athlete' s heart in 9 to 20-year-old male subjects.

The purpose of this cross-sectional investigation was to estimate the age at which specific traits of the "athlete's heart" first appear and how they evolve from the beginning of regular physical training until young adulthood in healthy active males. Male athletes (n=389) and non-athletes (n=55) aged between 9 and 20 years were examined by two-dimensionally guided M-mode and Doppler echocardiography. Intragroup differences were examined by t-tests for independent samples between age groups of two years each. Morphologic variables were related to body size by using ratio indices in which the power terms of numerator and denominator were matched. Relative left ventricular muscle mass (LVMM) was significantly larger in the athletic males at age of 11-12, and this significant difference was maintained with advancing age. Most of this increase of LVMM could be attributed to the increase in wall thickness that became significantly manifest first in the 13- to 14-year-old athletic subjects but was demonstrable in all the other groups. A significantly larger left ventricular internal diameter was only found in the age-group of 15-16. Fractional shortening percentage (FS%) did not show any change, while resting heart rate was decreased in our athletic groups.

Negative functional effects of cGMP mediated by cGMP protein kinase are reduced in T 4 cardiac myocytes

We tested the hypothesis that in isolated rabbit cardiac myocytes, the negative functional effects of cyclic GMP are partly mediated by cyclic GMP-dependent protein kinase activity, and that these effects are altered in thyroxine (T 4, 0.5 mg/kg/day for 16 days)-induced hypertrophic myocytes. Using isolated ventricular myocytes from control ( N=8) and T 4 ( N=8) hypertrophic hearts, data for percent cell shortening (%) and maximum rate of contraction (μm/s) were collected using a video edge detector at baseline, after the addition of 10 −6 M 8-bromo-cyclic GMP (8-Br-cGMP), 10 −5 M 8-Br-cGMP, and 10 −6 M KT5823 (10-methoxy-10-methoxycarbonyl-9, 10, 11, 12-tetrahydro-9, 12-epoxy-(1 H)-diinidolo [1, 2, 3, f–g: 3′, 2′, 1′-k-j]-pyrrolidino-[3,4-i] [1,6]-benzodiazocin-2-methyl-1-one, cyclic GMP protein kinase inhibitor). Protein phosphorylation was determined autoradiographically after gel electrophoresis. In both control and T 4 myocytes, 8-Br-cGMP caused a significant decrease in percent shortening (5.56±0.49% to 3.02±0.47% in control and 4.34±0.33% to 3.13±0.17% in T 4 myocytes) and maximal rate of contraction 57.35±6.05 to 36.82±3.17 μm/s in control and 58.49±3.28 to 42.88±2.29 μm/s in T 4 myocytes). KT5823 significantly increased percent shortening to 3.77±0.28% and rate to 48.68±4.71 μm/s after 8-Br-cGMP only in control myocytes. In T 4 myocytes, the changes in percent shortening and rate after KT5823 were not significant. Protein phosphorylation was increased by 8-Br-cGMP in control and to a lesser extent in T 4 myocytes, but the increment was reduced by KT-5823 in control only. These data demonstrated that cyclic GMP had negative functional effects partially mediated by cyclic GMP protein kinase in control myocytes. Cyclic GMP also exerted negative functional effects in thyroxine-induced hypertrophic myocytes, but cyclic GMP protein kinase activity was not an important regulator of these effects in T 4 ventricular myocytes.

Endosonography for assessment of anorectal changes in patients with fecal incontinence

Our aim was to evaluate the anorectal changes in patients with fecal incontinence by using different endoultrasound techniques. Eighteen females with fecal incontinence and 14 healthy controls (females) were examined. Rigid linear transducer and 10 MHz radial scanning miniprobe were used. Statistically significant difference was found in the mean percentage of decreasing of the anorectal angle during contraction between healthy subjects (21.4%) and incontinent patients (7.5%). The mean percentage of shortening of the puborectal muscle length during squeezing was significantly lower in patients (9.6%) than in controls (17.9%). By means of miniprobe the anal sphincter defects were clearly demonstrated. Endosonography with a radial scanning miniprobe and rigid linear transducer ensures complex morphological and functional assessment of the anorectal region.

Effect of NaHCO3 on cardiac energy metabolism and contractile function during hypoxemia.

To examine the impact of administration of NaHCO3 on contractility and energy metabolism of the myocardium during hypoxemia. Regional myocardial hypoxia was induced in the left anterior descending (LAD) artery myocardium in anesthetized, open-chest dogs, using a perfusion circuit between the right atrium and the LAD artery, and a membrane oxygenator. The rate of flow in LAD artery was maintained constant with the use of a roller pump. During hypoxia, eight dogs were administered isotonic NaHCO3 in the circuit and six other dogs received equimolar NaCl. Myocardial contractile function was assessed using sonomicrometry for measurement of percentage of systolic shortening and preload recruitable stroke work. Oxygen consumption and the rate of appearance of lactate were measured. Clamp-frozen tissue samples were obtained at the end of the experiment from the hypoxic LAD myocardium and the nonhypoxic circumflex myocardium for measurement of tissue lactate level. During hypoxia, there was a significant decrease in oxygen consumption by the LAD myocardium (35 +/- 7 micromol/min in the NaCl group and 40 +/- 7 micromol/min in the NaHCO3 group during hypoxia vs. 131 +/- 11 micromol/min during aerobic perfusion). There was also a significant decrease in myocardial contractility as measured by percentage of systolic shortening (14 +/- 3% to -8 +/- 3%); NaHCO3 infusion during hypoxia did not improve myocardial contractility (-7 +/- 2%). Similar results were obtained with measurements of preload recruitable stroke work. The rate of production of lactate during hypoxia was substantially lower than expected, based on the calculated oxygen deficit, and was not significantly increased by the administration of NaHCO3 (33 +/- 9 micromol/min in the NaCl group and 51 +/- 5 micromol/min in the NaHCO3 group). Tissue lactate was not statistically different in the hypoxic myocardium supplied by the LAD artery and the nonhypoxic myocardium supplied by the circumflex artery in either group. The response of the myocardium to hypoxia is to decrease its mechanical work and metabolic demand. The infusion of NaHCO3 did not enhance myocardial contractile function or flux in glycolysis during hypoxia. We speculate that this diminished mechanical work and metabolic demand may represent an adaptive response to preserve cellular integrity until oxygen delivery is restored.

Interaction between the opposing functional effects of cyclic AMP and cyclic GMP in hypertrophic cardiac myocytes.

We tested the hypothesis that in isolated cardiac myocytes, the negative functional effects of cyclic GMP would be blunted when the level of cyclic AMP was increased and that this interaction would be altered in renal hypertensive (One-Kidney-One-Clip, 1K1C) cardiac hypertrophic rabbits. Using isolated control and 1K1C ventricular myocytes, cyclic AMP and cell shortening (%) data were collected: 1) at baseline, 2) after the addition of 8-Br-cGMP 10(-7), -6, -5 M, and 3) after forskolin (10(-6) M), an adenylate cyclase activator, followed by 8-Br-cGMP 10(-7), -6, -5 M. Basal levels of cyclic AMP were similar in control vs. 1K1C myocytes (10.2 +/- 1.6 vs. 11.3 +/- 2.6 pmol/10(5) myocytes). We found that 8-Br-cGMP decreased the percent shortening in a dose related manner in both control myocytes (5.1 +/- 0.6 to 3.2 +/- 0.4%) and hypertrophic myocytes (5.2 +/- 0.4 to 3.6 +/- 0.5). The level of cyclic AMP significantly increased after the addition of 8-Br-cGMP in control myocytes (14.1 +/- 2.1), but not in 1K1C myocytes. Forskolin increased the percent shortening in the control myocytes (3.8 +/- 0.1 to 4.8 +/- 0.4), but no significant increase was noted in the hypertrophic myocytes (3.6 +/- 0.3 to 3.7 +/- 0.3). The level of cyclic AMP significantly increased after the addition of forskolin in both control (13.9 +/- 2.0), and 1K1C cells (14.6 +/- 3.8). Forskolin attenuated the negative functional effects of 8-Br-cGMP in the control (4.8 +/- 0.4 to 3.2 +/- 0.1) and 1K1C myocytes (3.7 +/- 0.3 to 2.7 +/- 0.3). The addition of 8-Br-cGMP did not affect the level of cyclic AMP after forskolin in either control (13.9 +/- 2.0 to 14.8 +/- 2.5) or 1K1C myocytes (14.6 +/- 3.8 to 13.8 +/- 1.9). These data indicated that in hypertrophic cardiac myocytes the negative functional effects of 8-Br-cGMP were similar to control, but the positive functional effects of cyclic AMP were blunted. There was an increase in cyclic AMP levels after addition of 8-Br-cGMP in control but not 1K1C cells. We conclude that in control and hypertrophic myocytes, the effects of cyclic GMP were blunted after forskolin, but this did not seem to be related to cyclic AMP phosphodiesterase activity.

Mechanical behaviour modelling of balloon-expandable stents

Endoprostheses are small struts placed by intravascular way to restore the vascular lumen and flow conditions. The purpose of this work is to provide models for evaluation and characterisation of some mechanical properties of a balloon-expandable stent by using the finite element method. Here we present the results for a metallic tubular peripheral prosthesis: the P308 Palmaz stent. We focus on the mechanisms linked to the structure expansion and its long-term behaviour. Several models are constructed in order to determine the stent shape after dilation and to assess the stress and strain fields in its wall due to this transformation. They inform us about the shortening percentage on expansion, degrees of radial and longitudinal recoil, and weaknesses of the structure. Various methods, differing in their levels of complexity, are then attempted to exhibit the predominant factors responsible for the crushing of a stent under external pressure. Moreover, the sensitivity of this critical pressure to geometric imperfections is studied. Lastly, since this kind of material is implanted for a lifetime, we test the stent with regard to fatigue life. Beyond safety considerations, this type of characterisation provides mechanical properties that are often difficult to obtain by experiments. If it was available for various stents, such information could be used to choose the appropriate prosthesis for specific applications. Moreover, confronted with observations from practitioners, they might lead to a better understanding of the failure or success of a particular design and to work on the product optimisation.