V3 Myosin Research Articles

In this issue

AbstractSooner or later, men, you'll get yourspp. 121–131Not death and taxes but something much more implacable because it is built into our biology – prostate problems. If prostate cancer doesn't get you, chances are benign prostatic hyperplasia (BPH) will. It's not usually fatal but “serious” and “life‐altering” are often heard when it is diagnosed. But diagnosis is another issue. There is no current test specific for BPH. Cheng et al. report here the results of chemists, statisticians and urologists applying proteomic techniques to this question. Using trypsin digests of urine specimens as the diagnostic material, they used MALDI‐TOF MS for pattern recognition to discriminate patients from well controls. Commercial software products were used for detailed data analysis. Statistical analysis identified nine potential marker candidates that were examined further. One was identified as CD14, but only in conjunction with PSA. It might also serve to distinguish BPH from prostate cancer. magnified imageAble to leap out of tall hutches in a single bound...and dies of heart failure.pp. 147–158How does he do that? He's SuperRabbit – that's what he does. So you want more details, do you? Then see Stanley et al. in this issue. Start with four parents (two rabbit, two human) in a snug Petri dish and make sure offspring inherit some reasonable share of human α‐myosin heavy chains (α‐MHC) and associated peripherals, including myosin light chains 1 and 2, and desmin, tropomysin, and troponin. You should have both transgenic and non‐transgenic animals. V1 myosin (α‐MHC) is a fast ATP burner, V3 (β‐MHC) is a slower but powerful ATP burner. The problem comes when the heart output is insufficient for the demand and tachycardia‐induced cardiomyopathy ensues. The functional roles of thick and thin filament proteins were analyzed by 1‐DE and 2‐D DIGE. Increased levels of UNC‐45B and TroponinT and uniform levels of UNC‐45A were confirmed. magnified imageProfiles as productspp. 179–188The wheel has been invented several times, at least metaphorically. This data brief from Schoenherr et al. aims to give breast cancer proteomic and transcriptional profilers a rest from the labors of reinventing those profiles. These 20‐some researchers from 3 different institutions have pooled their efforts to create a public library of state‐of‐the art “shotgun” LC‐MS/MS proteome profiles. Taken from a mouse model for human breast cancer (Her2/Neu), tumors can be readily turned on or off as a source of matched controls. Furthermore, no surgery is required, just a change in the medium induces the tumor. Research samples are available of the tissues profiled (thymus, spleen, liver, blood cells, plasma and breast). A total of 18 880 unique peptides were identified. magnified image

Thyroid state and tolerance of mammalian myocardium to hypoxia

Thyroid hormone is known to affect myocardial glycogen stores and thereby possibly limit anaerobic performance of mammalian cardiac muscle. Thyroid hormone administration (3,5,3'-triiodo-L-thyroxine, 300 microg/kg/day, sc) for 10 days decreased left ventricle (LV) glycogen concentration relative to euthyroid animals (2.78+/-0.46 vs. 4.28+/-0.29 mg/g of LV (mean+/-SEM)) while increasing the percent of V(1) myosin isozyme, contractile activity and cardiac mass. In contrast, thyroidectomy increased myocardial glycogen stores (8.50+/-0.56 mg/g of LV) and shifted the myosin isozyme toward V(3), prolonged contractile activity and decreased LV mass. Thyroxine administration for 3, 7 and 10 days to thyroidectomized animals progressively decreased contractile duration and increased LV mass. Thyroxine administration for 3 or 7 days to thyroidectomized rats did not reduce glycogen stores (7.75+/-1.02 and 9.62+/-1.16 mg/g of LV, respectively), whereas myocardial glycogen declined to 3.30+/-0.58 mg/g of LV after 10 days of treatment. During hypoxia, cardiac muscle from thyroidectomized rats maintained greater active force and developed less contracture relative to euthyroid and, to a greater extent, than hyperthyroid rats. Removal of glucose from the bath decreased anaerobic performance and impaired recovery; however, myocardium from thyroidectomized rats remained more tolerant to hypoxia than the euthyroid group. Overall, the intrinsic LV glycogen content was positively correlated to anaerobic performance. These data demonstrate that the thyroid state profoundly affects myocardial growth, contractility and anaerobic performance of rat myocardium. Although energy demand may affect function during hypoxia, anaerobic substrate reserve (cardiac glycogen concentration) appears to be the primary factor determining tolerance to hypoxic stress.

Acute Heart Failure—Basic Pathomechanism and New Drug Targets

In view of the high incidence of heart failure and sudden cardiac death, efforts in the development of compounds which target-specific mechanisms such as a reduced expression of SERCA2, the Ca2+ pump of sarcoplasmic reticulum, of hypertrophied cardiomyocytes of pressure-overloaded or infarcted hearts should be strengthened. Lead compounds for correcting a dysregulated gene expression are the carnitine palmitoyltransferase-1 (CPT-1) inhibitors etomoxir and oxfenicine. Since bypassing the CPT-1 inhibition by a medium-chain fatty acid diet had a lesser effect on myosin V1 proportion than on lipid droplet number, one has to infer also other mechanisms such as PPARalpha activation (FOXIB/PPARalpha). In view of the intricate interrelationship between depressed pump function and malignant arrhythmias, stimulation of endogenous antiarrhythmogenic mechanisms linked to an enhanced production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) could potentially provide alternatives to the administration of 1 g EPA and DHA ethyl esters (minimum 84% EPA + DHA) for secondary prevention of myocardial infarction. The apparently greater efficacy of omega-3 fatty acids in post-myocardial infarction patients (GISSI-Prevention study) compared with ICD patients (SOFA study) can be attributed to the greater ischemia-induced release of membrane-bound EPA and DHA and a better compliance (one vs. four capsules daily).

The expression pattern and cellular localisation of Myosin VI during the Drosophila melanogaster life cycle

Myosin VI is a motor protein which is necessary for the morphogenesis of epithelial tissues during Drosophila development. The spatial and temporal expression of Myosin VI was examined by expressing a GFP (Green Fluorescent Protein) tagged Myosin VI molecule (PGM), under the control of a Myosin VI-Gal4 line. PGM was present in tissues that were shown previously to express Myosin VI, such as the ovarian follicle epithelium, and the individualization complex; and in other tissues, including the trachea, the midgut, the salivary glands and the imaginal discs. The GFP-tagged Myosin V1 rescued the male sterile phenotype of Jaguar showing it is functional in vivo. Within individual cells, the role of the head and neck domain and the tail domain in targeting of the Myosin V1 molecule was examined by investigating the localisation of the separate domains tagged to GFP. In salivary glands and follicle cells the head and neck domains were concentrated in the cell nucleus, where the minus end of each actin filament is located. We found that the tail domain anchors the whole molecule outside of the nucleus. Similarly, in the individualization complex in the testes, the tail anchors the whole molecule to the base of the complex while the separated head with neck domain becomes scattered along the entire actin molecule suggesting the cellular location may be determined by cargo proteins that bind to the tail domain rather than by the movement of Myosin VI along the actin filaments.

Myosin from failing and non-failing human ventricles exhibit similar contractile properties

In non-failing human myocardium, V1 myosin comprises a small amount (<10%) of the total myosin content, whereas end-stage failing hearts contain nearly 100% V3 myosin. It has been suggested that this shift in V1 myosin isoform content may contribute to the contractile deficit in human myocardial failure. To test this hypothesis, myosin was isolated from human failing and non-failing ventricles, and non-failing atria. Performance was assessed in in vitro motility and isometric force assays. Consistent with prior reports, a small amount of V1 myosin was present in both non-failing (6.2 ± 1.0%) and failing (3.5 ± 1.4%) ventricular tissues. No difference in isometric force or unloaded shortening velocity was observed for failing and non-failing ventricular myosin irrespective of myosin isoform content. Atrial tissue expressing predominantly V1 myosin (66.7 ± 4.1%) generated half the force but greater velocity compared with ventricular tissue, expressing predominantly V3 myosin. In additional experiments, rabbit cardiac myosin was used in a calcium regulated assay system to determine if V1 and V3 isoforms differentially affect thin filament activation. Half-maximal calcium activation was similar for the two cardiac isoforms. A 1:9 mixture of V1/V3 myosin, simulating isoform composition in non-failing human myocardium, was indistinguishable from 100% V3 myosin (simulating the failing state) with regard to velocity of shortening and average force. These data suggest that the myosin isoform shift reported in human myocardial failure does not significantly contribute to the contractile deficit of this disease.

Losartan inhibits myosin isoform shift after myocardial infarction in rats.

Hypertrophy and heart failure following a myocardial infarction in rodents are accompanied by a switch of myosin isoforms from V1 to V3. The angiotensin II receptor blocker, Losartan, has been demonstrated to improve cardiac function and long-term survival after myocardial infarction. In this study we have investigated whether chronic Losartan treatment affects myosin isoform composition in the hearts of rats following a myocardial infarction. Rats were subjected to coronary artery ligation and received either Losartan (1 g/L) in the drinking water or water only. Four months after myocardial infarction, rats were classified as having either congestive heart failure (cMI) or uncomplicated myocardial infarction (uMI) based on their lung weight to body weight ratio (LW/BW). Compared with sham operated rats, uMI rats showed a 68.5% increase in the relative contribution of V3 and a 33.7% decrease in the relative contribution of V1 (p < 0.05). Untreated cMI showed 39.7% more V3 and 38.2% less V1 when compared with untreated uMI (p < 0.05). Losartan treatment after myocardial infarction reduced the incidence of cMI from 30.4 to 4.5% and scar size from 1.52 +/- 0.07 to 0.94 +/- 0.11 cm2 respectively. The percentage of V1 in Losartan treated uMI (LuMI) was 25.2% higher than the percentage of V1 in untreated uMI (p < 0.05), whereas the percentage of V3 in LuMI was 24.2% lower than that in untreated uMI (p < 0.05). A positive correlation of V3 myosin and scar area was observed. Our study suggests that expression of V3 myosin in the left ventricle is associated with scar size and the progress of hemodynamic changes after myocardial infarction. Losartan treatment reduces scar size and wall stress of the heart after the infarct, and therefore inhibits the signals shifting myosin isoform expression from V1 to V3 after a myocardial infarction.

Age-related differences in the effect of running training on cardiac Myosin isozyme composition in rats.

We examined the effect of running training on age-related changes in cardiac myosin isozyme composition in rats. Female Fischer 344 rats (6, 12, 20, and 27 months old) were divided into two groups: sedentary control and trained. The trained group rats were trained by treadmill running for up to 60 minutes per day, 5 days per week for 8 weeks at up to 30 m per minute. In sedentary control rats, the proportion of V1 myosin, that is, alpha-myosin heavy chain (MyHC) isoform, decreased progressively from 6 to 27 months of age. In the younger age groups (6 or 12 months old), there was a shift from V1 myosin to V3 myosin (beta-MyHC isoform) in trained hearts. However, the training program did not induce a cardiac myosin isozyme transition in older rats (20 or 27 months old). These results suggest that the mechanisms mediating the responses of cardiac muscle to running training alter during aging.

Characterization of sucrose-induced changes in cardiac phenotype.

The neuroendocrine factors responsible for long-term regulation of cardiac contractile performance remain ill defined. We examined influences of diet on the expression of myosin isozymes, sarcoplasmic reticulum (SR) Ca(2+) uptake and serum parameters. Dietary regimens (ad libitum feeding, intermittent fasting and 32% sucrose feeding) were used to alter the neurohumoral status of rats. Intermittent fasting decreased serum insulin levels ( P<0.05) and was associated with decreased SR Ca(2+) uptake and myosin V1 proportion ( P<0.05). Sucrose (32%) feeding increased myosin V1 of fasted and ad libitum fed rats ( P<0.05) but had no effect on insulin or SR Ca(2+) uptake. Expression of the alpha-myosin heavy chain correlated with serum insulin. Treatment of sucrose-fed rats with the sympatholytic compound moxonidine and the hypoglycaemic compounds BM13.907 and ciglitazone partially prevented the increase in myosin V1 ( P<0.05) but had no effect on SR Ca(2+) uptake and insulin. The data show that adrenergic activity and metabolic signals are important for an increase in myosin V1 in sucrose-fed rats, which can be associated with an unaltered SR Ca(2+) uptake rate.

Effect of aging and hypertension on beta-myosin heavy chain in heart of spontaneously hypertensive rats.

During aging rat myocardium undergoes structural changes characterized by a shift in the synthesis of myosin heavy chain (MHC) from V1 isoform, composed of two alpha-MHC, to V3 isoform, composed of two beta-MHC. In rat, besides ageing, cardiac hypertrophy as adaptive response to a superimposed pressure load (such as hypertension) is characterized by predominance of V3 myosin isoform. The aim of our study was to evaluate the expression of beta-MHC in right (RV) and left (LV) ventricles of spontaneously hypertensive rats (SHRs), a well defined animal model of hypertension, in relation to aging. We used very young (8-week old) and young (15-week old) SHRs and age-matched normotensive Harlan Sprague-Dawley control rats. By Western analysis, we found that beta-MHC is already present in both RV and LV of 8-week old SHRs, and is markedly predominant in RV and LV of 15-week old SHRs, when compared with age-matched control rats. Our study showed that the shift to V3 myosin isoform in SHRs is an early event, resembling accelerated senescence. We have also demonstrated that beta-MHC is actively synthesized also in young (15-week old) normal rats.

Altered Expression of Cardiac Myosin Isozymes Associated with the Malignant Hyperthermia Genotype in Swine

Anesthetic-induced malignant hyperthermia (MH) in humans and pigs is associated with dramatic alterations in cardiac function. However, it remains controversial as to whether MH-associated cardiac symptoms represent a primary difference of myocardium or a secondary alteration consequent to increases in the hyperthermic stress. Here the authors describe changes in myosin isoform expression in the hearts of MH-susceptible pigs with and without prior exposure to halothane. One group of pigs was diagnosed as MH susceptible by halothane challenge and Hal-1843 nucleotide examination. To determine if there is an effect of halothane exposure, another group of pigs was diagnosed by simple MH genotyping without exposure to halothane. After diagnosis and genotyping, animals with and without exposure to halothane were killed to study cardiac myosin isozyme distributions, cardiac myofibrillar adenosine triphosphatase (ATPase) activity, and the steepness of the Ca2+-ATPase activity relation in the hearts of normal and susceptible pigs. The altered myosin isozyme expression was analyzed by pyrophosphate gel electrophoresis. Malignant hyperthermia-susceptible animals with the prior halothane challenge showed an increased V1 myosin (-44%) expression, increased myofibrillar ATPase activity (-25%) and increased steepness of the Ca2+-ATPase activity relation. Without exposure to halothane, no change of myofibrillar ATPase activity was found in the hearts of different genotyped pigs, but there was a small increase in expression of V1 myosin (-5%) in the mutant (TT). The potential modulation of V1 myosin expression occurs in the hearts of MH-susceptible pigs. The added stress by halothane challenge would further cause a V3 --> V1 shift, which may be attributed to the long-term effects of hyperthermic stress.

2-deoxy-ATP enhances contractility of rat cardiac muscle.

To investigate the kinetic parameters of the crossbridge cycle that regulate force and shortening in cardiac muscle, we compared the mechanical properties of cardiac trabeculae with either ATP or 2-deoxy-ATP (dATP) as the substrate for contraction. Comparisons were made in trabeculae from untreated rats (predominantly V1 myosin) and those treated with propylthiouracil (PTU; V3 myosin). Steady-state hydrolytic activity of cardiac heavy meromyosin (HMM) showed that PTU treatment resulted in >40% reduction of ATPase activity. dATPase activity was >50% elevated above ATPase activity in HMM from both untreated and PTU-treated rats. V(max) of actin-activated hydrolytic activity was also >50% greater with dATP, whereas the K(m) for dATP was similar to that for ATP. This indicates that dATP increased the rate of crossbridge cycling in cardiac muscle. Increases in hydrolytic activity were paralleled by increases of 30% to 80% in isometric force (F(max)), rate of tension redevelopment (k(tr)), and unloaded shortening velocity (V(u)) in trabeculae from both untreated and PTU-treated rats (at maximal Ca(2+) activation), and F-actin sliding speed in an in vitro motility assay (V(f)). These results contrast with the effect of dATP in rabbit psoas and soleus fibers, where F(max) is unchanged even though k(tr), V(u), and V(f) are increased. The substantial enhancement of mechanical performance with dATP in cardiac muscle suggests that it may be a better substrate for contractility than ATP and warrants exploration of ribonucleotide reductase as a target for therapy in heart failure.

Angiotensin II–induced cardiomyocyte hypertrophy and cardiac fibrosis in stroke-prone spontaneously hypertensive rats

Angiotensin-converting enzyme inhibitors (ACEIs) cause regression of hypertensive left ventricular hypertrophy (LVH) by reducing angiotensin II, increasing bradykinin, or both. The mechanisms of these cardioprotective effects remain controversial. The aims of this study were to determine whether the cardioprotective effects of ACEIs are mediated by reducing angiotensin II and whether ACEIs ameliorate the morphologic, physiologic, and biochemical changes in the hearts of stroke-prone spontaneously hypertensive rats (SHRSPs). Male SHRSPs were treated with hydralazine, captopril, or candesartan, an angiotensin II type 1 receptor (AT1R) antagonist, from age 12 to 24 weeks. We measured systolic blood pressure (SBP), left ventricular weight (LVW), left ventricular (LV) myocyte cross-sectional area (myocyte size), LV interstitial collagen volume fraction (ICVF), perivascular collagen area/luminal area ratio (PVCA/LA), the medial area to luminal area ratio (MA/LA), the relative amount of V3 myosin heavy chain (MHCV3), and coronary reserve maximum (coronary flow max/ventricular weight [CFmax/VW]). These parameters were compared with those of untreated SHRSPs and Wistar-Kyoto rats (WKYs). SHRSPs exhibited decreased coronary reserve and LVH with an increase in myocyte size, PVCA/LA, MA/LA, and MHCV3 at 12 weeks of age. In addition to these changes, 24-week-old SHRSPs showed an increase in ICVF. The LVW, coronary reserve, myocyte size, PVCA/LA, ICVF, and MHCV3 of SHRSPs treated with captopril or candesartan all approached control values. In contrast, hydralazine decreased only ICVF. These results suggest that ACEIs regress LVH and normalize coronary reserve by modulating the effects of angiotensin II via AT1R on the induction of cardiomyocyte hypertrophy, perivascular fibrosis, and medial thickening of intramyocardial coronary arteries in SHRSPs. We concluded that these effects, in addition to the reduction of SBP, are important in causing the regression of LVH. (J Lab Clin Med 2000;135:353-9)

ラット心筋の局所的ミオシンアイソザイム構成比に及ぼすランニングトレーニングの影響

We examined the effect of running training on regional cardiac myosin isozyme composition in rats. Male Sprague-Dawley strain rats (4 weeks old) were used, and divided into two groups: sedentary control (C) and trained (T) groups. The T group was trained by treadmill running (40 m/min, 1h/day, 5 days/week, for 12 weeks) . At 16 weeks old, their hearts were excised. The left ventricle was separated into the subendocardium (Endo) and subepicardium (Epi) by dissecting the ventricle at the mid-wall. The ventricular myosin isozymes were examined by electrophoresis on pyrophosphate gel under non-dissociating conditions. The results showed the following: 1) The relative heart weight of the T group was significantly higher than the C group. 2) Left ventricular myosin isozyme composition showed a region-specific distribution in the C rats, and the proportion of V3 myosin or β-myosin heavy chain in the Endo was significantly higher than that of the Epi. However, the training had no effect on the cardiac myosin isozyme in either portion. 3) The activity of citrate synthase did not show transmural gradient in the ventricle of C animals. Training had no effect on the activities of either portion. 4) The activity of lactate dehydrogenase (LDH) showed transmural gradient in the ventricle of C rats. Training-induced changes in the activity of LDH were found in both portions, therefore, training abolished the transmural gradient in the activity of LDH, suggesting a corresponding redistribution of the myocardial work load.These results indicate that running training might induce the redistribution of the myocardial work load, whereas the stimulation apparently has no effect on the regional distribution of cardiac myosin isozyme composition.

Kinetic differences at the single molecule level account for the functional diversity of rabbit cardiac myosin isoforms.

1. Cardiac V3 myosin generates slower actin filament velocities and higher average isometric forces (in an in vitro motility assay) when compared with the V1 isoform. 2. To account for differences in V1 and V3 force and motion generation at the molecular level, we characterized the mechanics and kinetics of single V1 and V3 myosin molecules using a dual laser trap setup. 3. No differences in either unitary displacement (approximately 7 nm) or force (approximately 0.8 pN) were observed between isoforms; however, the duration of unitary displacement events was significantly longer for the V3 isoform at MgATP concentrations > 10 microM. 4. Our results were interpreted on the basis of a cross-bridge model in which displacement event durations were determined by the rates of MgADP release from, and MgATP binding to, myosin. 5. We propose that the release rate of MgADP from V3 myosin is half that of V1 myosin without any difference in their rates of MgATP binding; thus, kinetic differences between the two cardiac myosin isoforms are sufficient to account for their functional diversity.

The molecular mechanism of cardiac hypertrophy and failure.

Mechanical stretch induced by high blood pressure is an initial factor leading to cardiac hypertrophy. In an in vivo study, an angiotensin II (AngII) type 1 receptor antagonist TCV116 reduced left ventricular (LV) weight, LV wall thickness, transverse myocyte diameter, relative amount of V3 myosin heavy chain, and interstitial fibrosis, while treatment with hydralazine did not. In an in vitro study using cultured cardiomyocytes, mechanical stretch activated second messengers such as mitogen-activated protein (MAP) kinase, followed by increased protein synthesis. Additionally, in the stretch-conditioned medium AngII and endothelin-1 concentrations were increased. Furthermore, the Na+/H+ exchanger activated by mechanical stretch modulated the hypertrophic responses of cardiomyocytes. The pathways leading to MAP kinase activation differed between cell types. In cardiac fibroblasts AngII activated MAP kinase via G beta gamma subunit of Gi, Src, Shc, Grb2, and Ras, whereas Gq and protein kinase C were critical in cardiomyocytes.

Age-related difference in cardiac adaptation to chronic hypertension in rats, with and without nifedipine treatment.

Three myosin isozymes, V1 (alphaalpha MHC = Myosin Heavy Chain gene), V2 (alphabeta MHC) and V3 (betaalpha MHC) that are identified in the cardiac ventricles of most mammals have been shown to shift to a V3 predominance pattern during cardiac growth and in response to left ventricular pressure overload, and to V1 predominance following anti hypertensive treatment. This study examined whether long-term hypertension impairs the ability of the adult heart to restructure myosin isozyme proportions. Using pyrophosphate gel electrophoresis, we studied proportions of cardiac myosin isozymes (V1 and V3) in young (16 weeks) and adult (36 weeks) spontaneously hypertensive rats (SHR), and following 12 weeks of nifedipine (N) treatment in age-matched SHR rats (SHR-N). The values of V1 and V3 myosin isozymes were derived by adding half of the value of V2 to each isozyme proportion. The V3 proportion in the young SHR control (SHR-C) group (49%) was 34% higher (p < 0.05) than in the young Wistar Kyoto control (WKY-C) group (37%). However, the proportion was similarly high, though not statistically significant, in both the adult SHRC (73%) and WKY-C (71%) groups. The proportion in the young SHR-N group (29%) was 41% lower (p < 0.05) than in the young SHR-C group (49%), and the proportion in the adult SHR-N group (47%) was 34% lower (p < 0.05) than in the adult SHR-C group (73%). The ratio of left ventricular weight to body weight (LVW/BW), which determines left ventricular hypertrophy (LVH), was higher in both young and adult SHR-C (26%, p < 0.05, and 42%, p < 0.05, respectively) than in WKY-C groups. The mean LVW/BW was 27% (p < 0.05) greater in adult than in young SHR-C rats. The LVW/BW in both age groups of treated SHR-N was similar to that in age matched WKY-C rats. Our study showed that a rise in the V3 level occurs in young hypertensive rats, but no rise occurs in the V3 level in adult hypertensive rats. High blood pressure seems to contribute to the high V3 level in young hypertensive rats, but in adult hypertensive rats, high blood pressure does not accentuate the V3 rise already acquired due to the aging process. Nifedipine treatment in both young and adult hypertensive rats prevented the V3 rise due to hypertension and to the aging process. This effect of nifedipine seems to be through its antihypertensive action.

Effect of ovariectomy in heart failure-prone SHHF/Mcc-facp rats.

The importance of the loss of ovarian function to the progression of hypertension and heart disease in women is controversial. We investigated whether ovariectomy would accelerate development of hypertension, congestive heart failure, and neurohumoral activation in adult spontaneous hypertension heart failure (SHHF) rats, a genetic model of heart failure. Six months after ovariectomy, no significant differences between control and ovariectomized rats were seen in systolic or diastolic blood pressure, left ventricular fractional shortening by echocardiography, or heart weight. Percent V1 myosin isozyme was significantly lower in ovariectomized rats. Northern blot analysis failed to show significant differences between groups in expression of hepatic angiotensinogen, renal renin, or left ventricular atrial or brain natriuretic peptide mRNA. In a second experiment, serial measures of systolic pressure and left ventricular shortening fractions failed to document a significant difference between control and ovariectomized rats as they developed heart failure, although there was a significant decline in shortening fraction in both groups at the age when regular estrous cycling naturally ceases. Survival time was similar between groups. In summary, ovariectomy of adult SHHF rats does not appear to affect the progression of genetically programmed hypertension and heart failure in this model.

Effect of trimetazidine and verapamil on the cardiomyopathic hamster myosin phenotype.

1. In this study we investigated whether long-term trimetazidine (anti-ischaemic drug) therapy alters the ventricular myosin heavy chain (MHC) isoform composition in a model of cardiomyopathy. 2. MHC isoforms were analysed in the native state by electrophoresis in a pyrophosphate buffer. Myosin isoform patterns were studied in cardiac muscle from cardiomyopathic hamsters (CMH) of the BIO 14:6 strain during the time course of the disease and compared with those of healthy golden hamsters (F1B). The correlation between myosin profile and Ca2+-activated ATPase activity was determined from 220 days. 3. At the stage of insufficiency (350 days), CMH presented the most abnormal phenotype with 53% V1-24% V3 compared to 79% V1-7% V3 (P<0.001), in F1B. Trimetazidine was administered to cardiomyopathic hamsters from the early stage of active disease (30 days) to the congestive stages (220-350 days). Within 65 days, trimetazidine treatment, in CMH and F1B, reduced V1 to a low level (53% and 62%, respectively), which remained constant throughout the treatment. This level was similar to that in 220 and 350 days-old untreated-CMH. In sharp contrast, a standard calcium blocker, verapamil, administered to CMH in the same conditions resulted in a higher V1 (about 70%) and higher global myosin ATPase activity from 220 days. 4. Previous results in terms of hypertrophy and survival, compared to these results, suggest that verapamil and trimetazidine treatments reveal a dissociation between ventricular hypertrophy and isomyosin distribution. In addition, the shift in favour of V3 may not necessarily be an aggravating factor of the disease but an adaptative compensatory event.

Cross-bridge dynamics in the contracting heart.

The mechanical characteristics of the myosin motor is one of the key determinants of ventricular function. In small mammals there are two myosin isoforms, V1 and V3, with profoundly different performance characteristics. We used myothermal and mechanical analysis of intact papillary muscles from thryoxine (V1) and popylthiouracil (V3) treated rabbit hearts to assess the mechanical attributes of the myosin cross-bridge cycle. The average cross-bridge force time integral for V1 papillary muscles is 0.15 +/- 0.02 pNs for the entire isometric twitch and 0.19 +/- 0.03 pNs for the portion of the isometric twitch between 0.9 peak isometric force for the rising and declining portions of the twitch. The ratio of V1/V3 for the cross-bridge force time integral for the entire twitch and at the peak of the twitch is 0.5 (p < 0.05) and 0.4 (p < 0.05), respectively. Since the peak of the twitch measurements minimize internal shortening only these will be presented below. The average unitary force and attachment time during the peak of the twitch for V1 hearts was 1.55 +/- 0.37 pN and 140 +/- 20 msec, respectively. The ratios of V1/V3 for these parameters were 0.6 (p < 0.05) and 0.8 (ns). The cycling rate and duty cycle for V1 were 4.37 +/- 0.81 cycles per head-second and 0.66 +/- 0.22. The ratios of V1/V3 for cycling rate and duty cycle were 2.8 (p < 0.05) and 2.7 (ns). These measurements are consistent with and help explain the energetic and mechanical function of the intact heart.

Efficient Inhibition of the Development of Cardiac Remodeling by a Long-Acting Calcium Antagonist Amlodipine

The purpose of the present study was to examine the effects of a long-acting calcium antagonist, amlodipine, on the development of cardiac remodeling. Dihydropyridine calcium antagonists have been used widely for many years in the treatment of hypertension and angina pectoris. It has been reported, however, that a prototype of dihydropyridines, nifedipine, does not reduce mortality of patients with ischemic heart disease, possibly because of reflex stimulation of the sympathetic nervous system. A calcium antagonist, amlodipine, has been reported to have potential benefits by virtue of a gradual onset of action and a long duration of effects. Amlodipine (8 mg/kg per day, once a day) or nifedipine (24 mg/kg per day, three times a day) was administered to spontaneously hypertensive 12-week-old rats for 12 weeks. Left ventricular wall thickness was measured by echocardiography, and relative amounts of myosin heavy chain isoforms were assessed by pyrophosphate gels. Expressions of "fetal type" genes and type 1 collagen gene were examined by Northern blot analysis. Amlodipine and nifedipine both markedly reduced systolic blood pressure. However, the decrease in systolic blood pressure caused by nifedipine continued for no more than 8 hours, whereas the blood pressure-lowering effect of amlodipine continued for more than 16 hours post dose. Amlodipine markedly reduced left ventricular wall thickness, whereas nifedipine only weakly attenuated an increase in the wall thickness. Amlodipine, but not nifedipine, prevented an increase in the relative amount of V3 myosin heavy chain isoform and suppressed an increase in mRNA levels of beta-myosin heavy chain, skeletal alpha-actin, and type 1 collagen. Unlike nifedipine, amlodipine effectively prevented cardiac remodeling secondary to high blood pressure at biochemical levels and morphological levels. These results suggest that a long-acting calcium antagonist is more effective than a short-acting one in preventing organ injury in hypertensive subjects.