The myofibrillar ATPase activity and the substructure of myosin in the hypertrophied left ventricle of the rat

Impaired ATP turnover and ADP supply depress cardiac mitochondrial respiration and elevate superoxide in nonfailing spontaneously hypertensive rat hearts

Although most attention has been focused on mitochondrial ATP production and transfer in failing hearts, less has been focused on the nonfailing hypertensive heart. Here, energetic complications are less obvious, yet they may provide insight into disease ontogeny. We studied hearts from 12-mo-old spontaneously hypertensive rats (SHR) relative to normotensive Wistar-Kyoto (WKY) rats. The ex vivo working-heart model of SHR showed reduced compliance and impaired responses to increasing preloads. High-resolution respirometry showed higher state 3 (with excess ADP) respiration in SHR left ventricle fibers with complex I substrates and maximal uncoupled respiration with complex I + complex II substrates. Respiration with ATP was depressed 15% in SHR fibers relative to WKY fibers, suggesting impaired ATP hydrolysis. This finding was consistent with a 50% depression of actomyosin ATPase activities. Superoxide production from SHR fibers was similar to that from WKY fibers respiring with ADP; however, it was increased by 15% with ATP. In addition, the apparent K(m) for ADP was 54% higher for SHR fibers, and assays conducted after ex vivo work showed a 28% depression of complex I in SHR, but not WKY, fibers. Transmission electron microscopy showed similar mitochondrial volumes but a decrease in the number of cristae in SHR mitochondria. Tissue lipid peroxidation was also 15% greater in SHR left ventricle. Overall, these data suggest that although cardiac mitochondria from nonfailing SHR hearts function marginally better than those from WKY hearts, they show dysfunction after intense work. Impaired ATP turnover in hard-working SHR hearts may starve cardiac mitochondria of ADP and elevate superoxide.

Is the failing heart out of fuel or a worn engine running rich? A study of mitochondria in old spontaneously hypertensive rats

Hypertension now affects about 600 million people worldwide and is a leading cause of death in the Western world. The spontaneously hypertensive rat (SHR), provides a useful model to investigate hypertensive heart failure (HF). The SHR model replicates the clinical progression of hypertension in humans, wherein early development of hypertension is followed by a long stable period of compensated cardiac hypertrophy that slowly progresses to HF. Although the hypertensive failing heart generally shows increased substrate preference towards glucose and impaired mitochondrial function, the cause-and-effect relationship between these characteristics is incompletely understood. To explore these pathogenic processes, we compared cardiac mitochondrial proteomes of 20-month-old SHR and Wistar-Kyoto controls by iTRAQ-labelling combined with multidimensional LC/MS/MS. Of 137 high-scoring proteins identified, 79 differed between groups. Changes were apparent in several metabolic pathways, chaperone and antioxidant systems, and multiple subunits of the oxidative phosphorylation complexes were increased (complexes I, III and IV) or decreased (complexes II and V) in SHR heart mitochondria. Respiration assays on skinned fibres and isolated mitochondria showed markedly lower respiratory capacity on succinate. Enzyme activity assays often also showed mismatches between increased protein expression and activities suggesting elevated protein expression may be compensatory in the face of pathological stress.

Subcellular bases of cardiac disturbance in experimental informational neurosis

In experimental informational neurosis, accompanied by the development of stable arterial hypertension, tachycardia and dystrophic alterations in myocardium, the contractile protein ability to generate force and produce work as well as the power of the contractile process are significantly decreased and so is the intensity of Ca2+ transport through membranes of sarcoplasmic reticulum and mitochondria. Ca2+ content in these structures and energetic supply to the cardiac muscle do not change as compared with the control. Noradrenaline content in myocardium increases 5-fold compared with the control and 2.5-fold compared with the norm, while blood content falls to zero (sympathetic neuro-muscular contact is 'locked up' for noradrenaline outflow into the blood); dopamine content increases. Adenylate cyclase sensitivity to the stimulating effect of noradrenaline and NaF diminishes. Basal activity of phosphodiesterase increases, and its sensitivity to the inhibitory action of high calcium concentrations decreases. The disturbance in these systems may, on the one hand, be due to neural effects, and pressure overload of the heart, on the other hand, to the sharp rise in noradrenaline content in the myocardium and the change in the activity of cyclic adenosine monophosphate enzymes. It is suggested that similar changes may take place in the human myocardium and may underlie the cardiac weakness.

Alterations in the plasma membrane properties of the myocardium of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were used to investigate the adaptive biochemical changes in the myocardium in response to chronic afterload. Ouabain-inhibited Na+,K+-adenosine triphosphatase (ATPase) activity was decreased by 40% in myocardium of SHR compared with that from WKY, which may lead to increased intracellular Ca2+ through Na+-Ca2+ exchange. Similarly, alpha 1-adrenergic receptor density, estimated by [3H]prazosin binding, was decreased by 42% in myocardial membranes of SHR, while the affinity for the agonist and the antagonist was not altered. In contrast, the number of Ca2+ channels estimated by [3H]nitrendipine binding was increased by 45% in myocardial membranes of SHR, while the affinity was comparable between SHR and WKY. These differences between WKY and SHR in the membrane properties were not due to differential contamination of plasma membranes because the activities of other putative plasma membrane marker enzymes were comparable between WKY and SHR. There were no differences between WKY and SHR in the myosin ATPase activity estimated using myofibrils, actomyosin, and myosin. These results suggest that specific alterations have occurred in the plasma membrane properties of myocardium of SHR that result in altered intracellular Ca2+ metabolism. These alterations may have an important bearing on excitation-contraction coupling in myocardium of SHR.

Thin myofilament proteins in norm and heart failure. I. Polymerizability of myocardial Straub actin in acute and chronic heart failure

The reduced and intrinsic viscosities of myocardial Straub F-actin from the left ventricle of a practically healthy man were equal to 3.05 +/- 0.2 and 2.4 +/- 0.32 and from the right ventricle were 2.37 +/- 0.2 and 2.1 +/- 0.3 dl/g, respectively (the difference between ventricles was not significant). The average length of filaments measured by flow birefringence technique was equal to 1.3 +/- 0.04 micron, the number-average length (Ln), determined by the electron microscopy was 1.4 micron, the weight-average length (Lw), was 2 microns and the maximal one was 5.5 microns. The histograms showed that the most characteristic length was that of 0.8-1.2 micron. According to the flow birefringence data canine myocardial F-actin had a length similar to that of myocardial F-actin from a practically healthy man, though its reduced and intrinsic viscosities were higher. In acute and especially chronic congestive heart failure the actin polymerizability was sharply reduced. In consequence, in acute heart failure the number-average length of F-actin filaments was decreased by 43% and in congestive heart failure by 65.7%. The characteristic length in acute heart failure shifts to the range of 0.2-0.6 micron, while in congestive heart failure the range is 0.2-0.4 micron. This fact can possibly explain why during preparation of actin from the pathologically changed myocardium according to the methods including purification by the cycles of polymerization-sedimentation-depolymerization, the pathologically changed actin is discarded and the normal actin remains. A definite parallel was observed between the reduction of actin polymerizability and the ability of myocardial glycerinated fiber bundles (MBGF) to generate force. We conclude that the changes of actin properties in heart failure may cause a decrease in contractibility of the myocardial contractile protein system.

Myosin isoenzyme changes in several models of rat cardiac hypertrophy

We studied the effect of chronic mechanical overloading on the isoenzyme composition of rat cardiac myosin in several experimental models: aortic stenosis (AS), aortic incompetence (AI), aortocaval fistula (ACF), overload of the non-infarcted area after left coronary ligation (INF), and overload of the spontaneously hypertensive rats (SHR). Samples of the left and right ventricles were isolated from these hearts, and myosins were analyzed by electrophoresis in non-dissociating conditions. The myosin isoenzymes were called V1, V2, and V3 in order of decreasing mobility, according to the nomenclature of Hoh et al. Controls of the Wistar and Wistar Kyoto (WKY) strains were almost exclusively V1, A slow age-dependent shift toward V3 was observed in the left ventricles of adult Wistar rats, which at 30 weeks of age (body weight 600 g) contained approximately 15% of this form. In all models of cardiac hypertrophy, an isoenzymic redistribution was observed with a significant increase in V3. The level of V3 was statistically correlated with the degree of hypertrophy in the AS, (n = 11, r - 0.6, P less than 0.05), the AI (n = 14, 4 = 0.88, P less than 0.001), and the AS + AI(n = 14, 4 = 0.69, P less than 0.01) but not in the ACF (n = 16, r = 0.46). The isoenzymic changes could account for the decreases in both myosin ATPase activity and cardiac contractility described previously in our laboratory and by others. They also demonstrate that changes in myosin isoenzymes represent a general response of the rat heart, to chronic mechanical overloading.

The adaptive changes in the isoenzyme pattern of myosin from hypertrophied rat myocardium as a result of pressure overload and physical training

The distribution of cardiac myosin isoenzymes is altered as a result of pressure overload and physical training. Using polyacrylamide gel electrophoresis in sodium pyrophosphate, it was found that myosin from left ventricles of adult rats exists in three polymorphic forms, V1, V2 and V3. Cardiac hypertrophy due to renal hypertension (Goldblatt II) led to a shift of the isoenzymes towards V3, whereas swimming training resulted in an opposite redistribution. The isoenzyme V1 predominated, only traces of V2 and V3 were detectable. The changes in the isoenzyme distribution were reflected in an altered ATPase activity of myofibrils. In a representative sample of the Goldblatt rats, the activity was reduced by 11%, and the swimming training led to an increase by 10%. Changes in myofibrillar ATPase can, therefore, be traced to alterations in the isoenzyme pattern of myosin. The polymorphism of myosin has a two-faced aspect as regards cardiac performance. For example, a shift towards V3 is expected to increase the economy for tension development during isovolumetric contraction at the expense of a reduced maximum speed of ventricular contraction.