Reduced cardiac myosin adenosinetriphosphatase activity in dogs with spontaneously occurring heart failure

Changes in myocardial contractile protein ATPases in chronically adrenalectomized rats with and without glucocorticoid replacement

Studies were conducted to examine the effects of chronic adrenalectomy (Adx) and adrenalectomy plus glucocorticoid replacement therapy on rat cardiac contractile protein ATPase activities. The Ca2+-dependent Mg-ATPase activity of myofibrils isolated from rat ventricles 3 weeks postadrenalectomy (Adx) was significantly decreased at all pCa2+ concentrations (P less than 0.01), compared to sham-operated (SO) rats. Similarly, Ca2+-, K+-EDTA, and actin-activated myosin ATPase activities of Adx rat hearts were markedly decreased below that of SO rats (P less than 0.01). Dexamethasone administration to Adx rats prevented the decrease of Ca2+- and K+-ATPase activities of myosin, but not of myofibrillar Ca2+-dependent Mg-ATPase or actin-activated myosin Mg-ATPase activities. These studies suggest that glucocorticoid insufficiency induced by adrenalectomy results in altered myocardial contractile protein ATPase activity which may underlie impaired cardiac performance.

Human myocardial adenosine triphosphatase activities in health and heart failure

This study was designed to determine: (1) the myocardial adenosine triphosphatase (ATPase) activities of normal humans and patients with dilated cardiomyopathy and (2) whether ATPase activity is related to age, cause and severity of heart failure, and digitalis therapy. Endomyocardial biopsies were performed in 32 subjects. Results from six were normal. Ventricular failure in the other 26 was idiopathic (n = 15), familial (n = 3), alcohol induced (n = 5), or related to doxorubicin therapy (n = 3). The biopsies were analyzed for total, mitochondrial, Na+-K+, Ca++, and Mg++ ATPase activities. Total and mitochondrial ATPase activities correlated with left ventricular ejection fraction (r = 0.65 and 0.67, respectively; both p = 0.0001). Residual Mg++ ATPase activity correlated weakly with ventricular function as measured by echocardiography (p = 0.05). Na+-K+ ATPase activity was depressed in patients receiving digitalis (p = 0.01). These results suggest that progressive ventricular dysfunction may be associated with a progressive loss of total ATPase, mitochondrial ATPase and, to a lesser extent, Mg++ ATPase activity. Although depressed mitochondrial ATPase activity is not likely to be the primary cause of ventricular dysfunction, it could perpetuate failure by leading to inadequate production of adenosine triphosphate. Further study of ATPase activities may provide additional insight into the pathogenesis of cardiac failure.

cAMP regulation of myosin ATPase activity in the maturing rat heart

Calcium-activated myosin adenosine triphosphatase (ATPase) activity has been measured in sections of rat ventricles that were rapidly frozen to preserve the structure and regulatory state of myosin occurring in vivo. These results were related to myosin isozyme composition measured in ventricles by native gel electrophoresis and by quantitative immunocytochemistry. Both total ATPase activity and percent alpha-heavy chain rapidly rise during the first month following birth. However, ATPase activity remains constant at a high level from 1 to 12 months following birth, even though percent alpha-heavy chain declines during this period. The ATPase activity of V1 myosin was specifically determined using sections in which V3 myosin had been completely inhibited by exposure to alkaline pH in the absence of adenosine 5'-triphosphate (ATP). Relative V1 specific activity, taken as the ratio of V1 ATPase activity to percent alpha-heavy chain, doubles in the first 2.0 months after birth and then remains approximately constant at this higher level until at least 4 months after birth. The specific activity of V1 can be further increased by the addition of adenosine-3',5'-cyclic monophosphate (cAMP). This effect of cAMP is age dependent, increasing threefold between 1 and 2 months following birth and then declining as V1 is replaced by V3.

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.

Hormonal influences on cardiac myosin ATPase activity and myosin isoenzyme distribution

It has been recognized for a long time that changes in hormone secretion can influence cardiac function; however, the biochemical basis for these changes has only recently been clarified. In this review the influences of hormonal status on the contractile protein myosin is discussed. Myosin has a rod-like portion and a globular head and consists of two myosin heavy chains (MHC) and four light chains (LC), two of which are identical. The globular head is the site of an ATP-splitting enzyme, the myosin ATPase, and increases in myosin ATPase activity are closely related to an increased velocity of contraction of the heart. Myosin ATPase activity shows marked response to alterations in thyroid hormone, insulin, glucocorticoid, testosterone and catecholamine levels, but marked animal species differences in this response occur. Thyroid hormone administration to normal rabbits, for example, increases myosin ATPase activity markedly, but the myosin ATPase activity of hyperthyroid rats remains unchanged. In contrast, in hypothyroid rats myosin ATPase activity is markedly decreased but the hypothyroid rabbit shows no such response. These species-related differences in the hormonal response of myosin ATPase activity result from the predominance pattern of specific myosin isoenzymes. In the normal rat heart three myosin isoenzymes, V1, V2 and V3, can be separated electrophoretically. Myosin V1 predominates (70% of total myosin), and has the highest myosin ATPase activity, whereas in rabbits myosin V3, which has a lower myosin ATPase activity, is the predominant isomyosin. Thyroid hormone administration to rabbits induces myosin V1 predominance and therefore increases myosin ATPase activity, whereas in hyperthyroid rats only a small further increase in V1 predominance can occur. The alterations in myosin isoenzyme predominance and myosin ATPase activity are closely correlated to changes in cardiac contractility. Hormone-induced alterations in myosin isoenzyme predominance are mediated through changes in the formation of two isoforms of myosin heavy chain. Changes in the expression of different myosin heavy chain genes are most likely responsible for the thyroid hormone and insulin-induced alterations in myosin isoenzyme predominance. Investigation of the control of myosin heavy chain formation can provide further insights into the hormonal control of a multigene family as well as broaden our understanding of the molecular events which result in altered cardiac contractility.(ABSTRACT TRUNCATED AT 400 WORDS)

Myosin isoenzyme redistribution in chronic heart overload

Since the first observation by Spann et al., it has become clear that in cardiac hypertrophy induced by a mechanical overloading, the velocity of shortening of the cardiac muscle (Vmax) is reduced (see ref. 2 for review). Most authors agree that this mechanical alteration is accompanied by a decrease in the Ca2+-dependent ATPase activity of myosin (see ref. 3 for review). The molecular basis of such changes was unknown because the structural modifications of the myosin molecule were ill-defined. Nevertheless, it has recently been shown that, like skeletal muscle myosin, cardiac myosin is composed of several polymorphic forms, comparable to isoenzymes. In the skeletal muscle, new functional requirements can induce changes in both contractile activity and type of myosin isoenzyme synthesised. We now report that an increase in cardiac work produced by mechanical overloading in rats induces the preferential synthesis of a cardiac myosin isoenzyme characterised by specific immunological and electrophoretic properties and exhibiting a lower ATPase activity. This adaptive change could account for the reduced shortening speed of this hypertrophied cardiac muscle.

Cardiac contractile proteins. Adenosine triphosphatase activity and physiological function

This review has pointed out the good correlation frequently observed between ATPase activity of various contractile protein preparations and contractile function of various muscles including the myocardium. Some of the variables in the measurement of the various ATPases and the relationship of these measurements to physiological ATPase in the intact myofibril have been mentioned. The possible roles of changes in the light chains of sulfhydryl groups in the control of ATPase activity have been outlined. The possibility that phosphorylating reactions might exert control over physiological activity remains to be clarified. It is evident that, despite the large amount of research that has been done, our understanding of how the biochemistry of contractile proteins relates to physiological function is in its infancy, and only with a more complete elucidation of the underlying biochemistry of the components of contractile proteins of physiological and pathophysiological adaptations become evident.

Calcium sensitivity of myocardial actomyosin ATPase in young and mature male Fischer rats. A brief note

Although myocardial actomyosin ATPase specific activity determined at Ca2+ levels of 1 x 10(-3) to 1 x 10(-2) M is consistently higher in two-month old male Fischer rats than in twelve-month old individuals, this difference can be eliminated if the enzyme is assayed at lower calcium concentrations. This suggests that the previously reported, declining actomyosin ATPase activity in the rat myocardium with advancing age may represent an age-related diminished ability of calcium to reverse the known inhibition upon actomyosin ATPase by the regulatory proteins.

The amino acid composition of actin and myosin and Ca2+-activated myosin adenosine triphosphatase in chronic canine congestive heart failure

The Ca2+-activated myosin ATPase and the amino acid compositions of actin and myosin were determined for preparations from chronically failing dog hearts. Hypertrophy and congestive heart failure were produced by combined tricuspid valve insufficiency and pulmonary artery stenosis. Control, shamoperated, and noncardiac circulatory failure (inferior vena cava constriction) dogs also were studied. All hearts were divided into right ventricle, septum and left ventricle and each sample was individually analyzed. Calcium-activated ATPase decreased in the failing hearts and showed a distinct gradient of depression from right to left ventricles. There were no changes in ATPase activity among the other groups. The amino acid composition of actin was the same regardless of origin. The amino acid composition of myosin was unaltered except that cystine/2 residues were markedly decreased in failing heart myosin. The same gradient of depression was present as was found for Ca2+-activated myosin ATPase. This study suggests that protein metabolism is abnormal and that altered proteins are produced in hypertrophy and congestive heart failure. It appears that these changes do not affect all proteins, since actin was normal by the parameters studied. It is clear that the stressed ventricle is the most severely involved, but the entire heart is altered to some degree. Thus, we conclude that altered protein metabolism may be an important primary factor in the genesis of heart failure.

Abnormalities in heart membranes and myofibrils during bacterial infective cardiomyopathy in the rabbit

We studied hearts from sham-operated and uninfected catheterized rabbits as well as from rabbits at early and late stages of cardiomyopathy and failure after 3 and 6 days of infection with Streptococcus viridans. No ultrastructural abnormalities or biochemical changes in membrane and myofibrillar activities were seen in 3-day uninfected hearts. In 6-day uninfected hearts there were decreased sarcolemmal M2+ ATPase, Na+-K+ ATPase, adenylate cyclase and calcium binding, microsomal calcium binding and uptake, and myofibrillar Ca2+-stimulated ATPase as well as increased mitochondrial calcium uptake. Slight ultrastructural changes also were apparent in 6-day uninfected hearts. At both early and late stages of infective cardiomyopathy and failure there were varying degrees of depression in sarcolemmal Mg2+ ATPase, Na+-K+ ATPase, adenylate cyclase and calcium binding, microsomal calcium binding, calcium uptake and basal ATPase, and myofibrillar Ca2+-stimulated ATPase activities. However, sarcolemmal Ca2+ ATPase and myofibrillar Mg2+ ATPase activities were decreased only after 6 days of infection. Mitochondrial calcium binding and uptake were increased in early stages but decreased in late stages of disease. Furthermore in infected hearts there were defects in mitrochondrial respiration and phosphorylation. Generalized severe myocardial cell damage involving myofibrils, mitochondria, and the sarcotubular system was seen only in late stages of infection. The results demonstrate impairment of different membrane and contractile protein functions as well as ultrastructural abnormalities in bacterial cardiomyopathic hearts which were absent or of lesser magnitude in hearts with only hypertrophy. The findings reported here suggest to use that there is an association between heart failure and changes in function of cellular components during bacterial infective cardiomyopathy.

Myofibrillar ATPase, DNA and hydroxyproline content of human hypertrophied heart

70 human hearts were studied less than 36 hours after death. The apex, and in some cases other parts of the myocardium were homogenized, DNA, hydroxyproline content, myofibrillar Ca2+ and Mg2+ ATPase were measured. In normal hearts the DNA and collagen content were 372 +/- 9 mg and 36 +/- 7 mg. Ca2+ and Mg2+ ATPase of the myofibrils prepared from these hearts have shown the same specific activity (35 +/- 5 and 34 +/- 6 nmol/min./mg) as those from fresh biopsies taken during open-chest surgery. The heart weight correlates with the DNA content (r= + 0.58 -p less than 0.01) and with the myofibrillar ATPase (r= - 0.33 - p less than 0.02) but not with the DNA concentration nor with the collagen content or concentration. The main result of this study was the presence of a negative correlation between the DNA content of the heart and the Mg2+ or Ca2+ myofibrillar ATPase (r= - 0.31, p less than 0.05 - r= - 0.45, p less than 0.01). This correlation was analysed with reference to the histological and biochemical studies published by several authors in human or experimental heart hypertrophy and it was suggested that in human heart hypertrophy the decrease of the myofibrillar or myosin ATPase is a direct consequence of the high degree of polyploidy of the muscular cells observed in this condition.

Heart contractile proteins

That several proteins of the sarcomere differ from one muscle to the next is well documented, and it is becoming evident that homogeneous muscles, like the heart, are also species specific. 1) Clear-cut evidence is available concerning myosin, and, to date, several types of molecules have been described. a) The myosins of white skeletal, heart, and smooth muscle differ in the activity of their Ca2+ and K+ATPases, as also in the structure of their light subunits. b) The Ca2+ATPases of the various cardiac myosins have been shown to exhibit species differences and correlate with the speed of shortening of the muscle. 2) The structures of tropomyosin, some troponin components, and alpha actinin (but not actin) appear to be unlike in the different types of muscle. 3) These phylogenic modifications may be related to the changes characteristic of the particular muscles under pathological conditions, which are accompanied by substantial increase in protein synthesis.

Editorial: Subunits of myosin. Relations to ATPase activity and mechanical function of muscle

Under certain conditions the specific ATPase activity of myosin of a given muscle can be altered. The cause of this alteration can only lie in the myosin molecule itself. To produce an enzymatic activity of myosin, an interaction between their light and heavy chains is necessary. However, the specific activity appears to be determined mainly by light chains. Hence, one ought also to look for a basis of the changed activity in changes of the subunits of myosin. There are strong indications that the alterations in specific activity are accompanied by changes in the relative stoichiometry of the essential light chains of the respective myosin preparation. They differ in their pattern of subunits. The specific activity of a given kind of myosin seems to be determined by the combination of their light chains. Thus, a close correlation exists between these two properties of myosin (ATPase activity and structure of its molecule). There are sufficient indications, that these two properties of myosin correlate also with the mechanical capabiltiy of the corresponding muscle. Particularly the results of cross innervation studies demonstrate a close correlation between these three properties in skeletal muscle. The single subunits of myosin are produced and degraded independently and at heterogenous rates. The synthetis of these subunits is significantly accelerated in response to work overload. Thus, it is quite likely that the individual chains are non-coordinately synthesized, giving rise to variations in the relationship of different molecule types of myosin with different specific ATPase activity. Hence, the control mechanism to synthesize the individual subunits could also be the regulative mechanism to produce a myosin of the specific ATPase activity appropriate to the activity pattern of tissue.

Human cardiac myosin ATPase and light subunits. A comparative study

Myosin was extracted from normal human hearts (autopsy material) and compared to that of pig heart and rabbit white skeletal muscle. Myosin light subunits were isolated by a preparative urea gel electrophoresis. These subunits were shown by urea and sodium dodecylsulfate gel electrophoresis to be only slightly affected by the time lapse between death and the beginning of myosin extraction. This was also true for myosin ATPases. The Ca-2+-activated ATPases of pig and human heart myosins have the same apparent Km and V, whereas white skeletal muscle myosin ATPase has the same Km with a higher V. Human myosin light subunits, when compared to those of pig heart possess: (i) different molecular weights: 27 999 and 18 000 datlons for pig heart, and 25 000 and 19 000 daltons for human heart. (ii) for both the light chains, different ultraviolet spectra and a higher helical content for the subunit molecular weight 25 000. (iii) a different composition for several amino acids (Tyr, Pro, Lys). A third light subunit (molecular weight 15 000) was occasionally seen in human as well as pig heart myosin. It concentration varied inversely with that of the subunit molecular weight 27 000-25 000, and so was probably a degradation product of the heaviest subunit.

Simultaneously measured isometric tension and ATP hydrolysis in glycerinated fibers from normal and hypertrophied rabbit heart

Adenosinetriphosphatase (ATPase) activity, isometric tension, and sarcomere length of glycerinated fibers from 14 hypertrophied and 18 normal rabbit hearts were measured simultaneously to characterize the altered performance of hypertrophied myocardium. ATPase activity was assessed radiochromatographically, and contributions from mitochondria, sarcolemma, and sarcoplasmic reticulum were excluded. The active length-tension and the active tension-pCa relationships in fibers from hypertrophied myocardium were normal in sharp contrast to the depressed active length-tension curves in corresponding intact papillary muscles. Total ATPase activity associated with contraction at a given developed tension was decreased significantly in fibers from hypertrophied hearts ( P <0.001). ATPase activity was diminished in glycerinated myofibrils, actomyosin, and homogenates from hypertrophied hearts as well. On the other hand, the increase in ATPase activity associated with a given increase in developed tension was virtually identical in fibers from hypertrophied and normal hearts. Thus, depressed total ATPase activity in glycerinated fibers from hypertrophied hearts does not appear to impair maintenance of isometric tension.

Cardiac impairment in adrenal insufficiency in the cat. Reduced adenosinetriphosphatase activity of myocardial contractile proteins

Cardiac contractile protein ATPase activity was studied in cats 10 days after adrenalectomy at a time when the mean arterial blood pressure was 27% lower than that of control cats. The Ca 2+ -dependent, azide-insensitive ATPase activity of myofibrils isolated from the ventricles of adrenalectomized cats was 63% of the activity of control preparations ( P <0.025). Similarly, the specific activities of cardiac actomyosin (myosin B) and myosin from adrenalectomized cats had decreased to 54 and 75% of control values, respectively ( P <0.005). The percent reductions in ATPase activities in the three protein preparations from adrenalectomized animals were not significantly different, suggesting that the depression was associated with myosin per se. The reduction in the myosin ATPase activity in adrenal insufficiency was prevented by dexamethasone treatment adequate to prevent the decline in mean arterial blood pressure of the adrenalectomized cats. The reduction in cardiac performance in frank adrenal insufficiency may reflect a decrease in the rate of conversion of chemical to mechanical energy by the myocardial contractile proteins.