Intracellular Ca2+ release and reuptake are essential for contraction and relaxation of normal heart muscle. Intracellular Ca2+ transients were recorded with aequorin during isometric contraction of myocardium from patients with end-stage heart failure. In contrast to controls, contractions and Ca2+ transients of muscles from failing hearts were markedly prolonged, and the Ca2+ transients exhibited 2 distinct components. Muscles from failing hearts showed a diminished capacity to restore low resting Ca2+ levels during diastole. These experiments provide the first direct evidence from actively contracting human myocardium that intracellular Ca2+ handling is abnormal and may cause systolic and diastolic dysfunction in heart failure.

The function of the heart is to contract and pump oxygenated blood to the body and deoxygenated blood to the lungs. To achieve this goal, a normal human heart must beat regularly and continuously for one's entire life. Heartbeats originate from the rhythmic pacing discharge from the sinoatrial (SA) node within the heart itself. In the absence of extrinsic neural or hormonal influences, the SA node pacing rate would be about 100 beats per minute. Heart rate and cardiac output, however, must vary in response to the needs of the body's cells for oxygen and nutrients under varying conditions. In order to respond rapidly to the changing requirements of the body's tissues, the heart rate and contractility are regulated by the nervous system, hormones, and other factors. Here we review how the cardiovascular system is controlled and influenced by not only a unique intrinsic system, but is also heavily influenced by the autonomic nervous system as well as the endocrine system.

In human and experimental models of heart failure, sarcoplasmic reticulum Ca 2؉ ATPase (SERCA2a) activity is decreased, resulting in abnormal calcium handling. The disturbances in calcium metabolism have been shown to contribute significantly to the contractile dysfunction observed in heart failure. We investigated whether increasing SERCA2a expression can improve ventricular function in an animal model of heart failure obtained by creating ascending aortic constriction in rats. After 19 -23 wk of banding during the transition from compensated hypertrophy to heart failure (documented by >25% decrease in fractional shortening), rats were randomized to receive either an adenovirus carrying the SERCA2a gene (Ad.SERCA2a, n ‫؍‬ 13) or ␤-galactosidase (Ad.␤gal, n ‫؍‬ 14) by using a catheter-based technique. The failing hearts infected with Ad.␤gal were characterized by a significant decrease in SERCA2a expression and a decrease in SERCA2a activity compared with nonfailing sham-operated rats (n ‫؍‬ 11). In addition, these failing hearts had reduced left-ventricular systolic pressure, maximal rate of left-ventricular pressure rise and decline (؉dP͞dt, ؊dP͞dt), and rate of isovolumic relaxation (). Overexpression of SERCA2a restored both SERCA2a expression and ATPase activity to nonfailing levels. Furthermore, rats infected with Ad.SERCA2a had significant improvement in left-ventricular systolic pressure, ؉dP͞dt, ؊dP͞dt, and rate of isovolumic relaxation () normalizing them back to levels comparable to sham-operated rats. In this study, we show that in an animal model of heart failure where SERCA2a protein levels and activity are decreased and severe contractile dysfunction is present, overexpression of SERCA2a in vivo restores both systolic and diastolic function to normal levels. B oth contraction and relaxation abnormalities at the cardiac myocyte level have been identified in human and animal models of heart failure (1, 2). Trabeculae and isolated cardiac cells from failing hearts have characteristic functional abnormalities, which include an increase in diastolic Ca 2ϩ , an increase in the time course of Ca 2ϩ transient, and a decrease in sarcoplasmic reticulum (SR) Ca 2ϩ release (1-3). These abnormalities are especially accentuated at high frequencies of stimulation leading to the characteristic negative force-frequency relationship in failing myocardium (4).Because the SR plays a central role in controlling Ca 2ϩ movements in myocardial cells during excitation-contraction coupling, a large number of studies have been performed examining the expression and function of the SR Ca 2ϩ ATPase (SERCA2a)(5-9). SERCA2a activity and SR Ca 2ϩ uptake are reduced in failing hearts (9). This reduction in activity is generally, but not invariably, associated with reductions in SERCA2a mRNA and protein. Taken together, these results support the hypothesis that abnormal Ca 2ϩ handling in failing hearts is caused in part by a decrease in SERCA2a activity.To examine the importance of SERCA2a in the development of decompensated heart...

Background-Ischemia-induced cardiomyopathy usually is accompanied by elevated left ventricular end-diastolic pressure, which follows from increased myocardial stiffness resulting from upregulated collagen expression. In addition to collagen, a main determinant of stiffness is titin, whose role in ischemia-induced left ventricular stiffening was studied here. Human heart sarcomeres coexpress 2 principal titin isoforms, a more compliant N2BA isoform and a stiffer N2B isoform. In comparison, normal rat hearts express almost no N2BA titin. Methods and Results-Gel electrophoresis and immunoblotting were used to determine the N2BA-to-N2B titin isoform ratio in nonischemic human hearts and nonnecrotic left ventricle of coronary artery disease (CAD) patients. The average N2BA-to-N2B ratio was 47:53 in severely diseased CAD transplanted hearts and 32:68 in nonischemic transplants. In normal donor hearts and donor hearts with CAD background, relative N2BA titin content was Ϸ30%. The titin isoform shift in CAD transplant hearts coincided with a high degree of modifications of cardiac troponin I, probably indicating increased preload. Immunofluorescence microscopy on CAD transplant specimens showed a regular cross-striated arrangement of titin and increased expression of collagen and desmin. Force measurements on isolated myofibrils revealed reduced passive-tension levels in sarcomeres of CAD hearts with high left ventricular end-diastolic pressure compared with sarcomeres of normal hearts. In a rat model of ischemia-induced myocardial infarction (left anterior descending coronary artery ligature), 43% of animals, but only 14% of sham-operated animals, showed a distinct N2BA titin band on gels. Conclusions-A titin isoform switch was observed in chronically ischemic human hearts showing extensive remodeling, which necessitated cardiac transplantation. The shift, also confirmed in rat hearts, caused reduced titin-derived myofibrillar stiffness. Titin modifications in long-term ischemic myocardium could impair the ability of the heart to use the Frank-Starling mechanism.

Background-The role of androgens in producing cardiac hypertrophy by direct action on cardiac myocytes is uncertain.Accordingly, we tested the hypothesis that cardiac myocytes in adult men and women express an androgen receptor gene and that myocytes respond to androgens by a hypertrophic response. Methods and Results-We used reverse transcription-polymerase chain reaction methods to demonstrate androgen receptor transcripts in multiple tissues and [ 3 H]phenylalanine incorporation and atrial natriuretic peptide secretion as markers of hypertrophy in cultured rat myocytes. Messenger RNA encoding androgen receptors was detected in myocytes of male and female adult rats, neonatal rat myocytes, rat heart, dog heart, and infant and adult human heart. Both testosterone and dihydrotestosterone produced a robust receptor-specific hypertrophic response in myocytes, determined by indices of protein synthesis and atrial natriuretic peptide secretion. Conclusions-Androgen receptors are present in cardiac myocytes from multiple species, including normal men and women, in a context that permits androgens to modulate the cardiac phenotype and produce hypertrophy by direct, receptor-specific mechanisms. There are clinical implications for therapeutic or illicit use of androgens in humans.(Circulation. 1998;98:256-261.)

Background-In heart failure, sarcoplasmic reticulum (SR) Ca 2ϩ -ATPase (SERCA2a) activity is decreased, resulting in abnormal calcium handling and contractile dysfunction. We have previously shown that increasing SERCA2a expression by gene transfer improves ventricular function in a rat model of heart failure created by ascending aortic constriction. Methods and Results-In this study, we tested the effects of gene transfer of SERCA2a on survival, left ventricular (LV) volumes, and metabolism. By 26 to 27 weeks after aortic banding, all animals developed heart failure (as documented by Ͼ25% decrease in fractional shortening) and were randomized to receive either an adenovirus carrying the SERCA2a gene (Ad.SERCA2a) or control virus (Ad.␤gal-GFP) by use of a catheter-based technique. Sham-operated rats, uninfected or infected with either Ad.␤gal-GFP or Ad.SERCA2a, served as controls. Four weeks after gene transfer, survival in rats with heart failure treated with Ad.␤gal-GFP was 9%, compared with 63% in rats receiving Ad.SERCA2a. LV volumes were significantly increased in heart failure (0.64Ϯ0.05 versus 0.35Ϯ0.03 mL, PϽ0.02).Overexpression of SERCA2a normalized LV volumes (0.46Ϯ0.07 mL) in the failing hearts. 31 P NMR analysis showed a reduced ratio of phosphocreatine to ATP content in failingϩAd.␤gal-GFP compared with shamϩAd.␤gal-GFP (0.82Ϯ0.13 versus 1.38Ϯ0.14, PϽ0.01). Overexpression of SERCA2a in failing hearts improved the phosphocreatine/ ATP ratio (1.23Ϯ0.28). Conclusions-In this study, we show that unlike inotropic agents that improve contractile function at the expense of increased mortality and worsening metabolism, gene transfer of SERCA2a improves survival and the energy potential in failing hearts.

In the failing heart, there is a clear prohypertrophic activity profile, likely occurring in response to increased systolic wall stress and neurohormonal mediators. However, with the activation of these hypertrophic pathways, potent proapoptotic and antiapoptotic signals may also be generated. Therapies directed at altering the balance of activity of these signaling pathways could potentially alter the progression of heart failure.

In the pathogenesis of dilated cardiomyopathy, cytoskeletal proteins play an important role. In this study, we analyzed titin expression in left ventricles of 19 control human donors and 9 severely diseased (nonischemic) dilated cardiomyopathy (DCM) transplant-patients, using gel-electrophoresis, immunoblotting, and quantitative RT-PCR. Both human-heart groups coexpressed smaller (approximately 3 MDa) N2B-isoform and longer (3.20 to 3.35 MDa) N2BA-isoforms, but the average N2BA:N2B-protein ratio was shifted from approximately 30:70 in controls to 42:58 in DCM hearts, due mainly to increased expression of N2BA-isoforms >3.30 MDa. Titin per unit tissue was decreased in some DCM hearts. The titin-binding protein obscurin also underwent isoform-shifting in DCM. Quantitative RT-PCR revealed a 47% reduction in total-titin mRNA levels in DCM compared with control hearts, but no differences in N2B, all-N2BA, and individual-N2BA transcripts. The reduction in total-titin transcripts followed from a decreased area occupied by myocytes and increased connective tissue in DCM hearts, as detected by histological analysis. Force measurements on isolated cardiomyofibrils showed that sarcomeric passive tension was reduced on average by 25% to 30% in DCM, a reduction readily predictable with a model of wormlike-chain titin elasticity. Passive-tension measurements on human-heart fiber bundles, before and after titin proteolysis, revealed a much-reduced relative contribution of titin to total passive stiffness in DCM. Results suggested that the titin-isoform shift in DCM depresses the proportion of titin-based stiffness by approximately 10%. We conclude that a lower-than-normal proportion of titin-based stiffness in end-stage failing hearts results partly from loss of titin and increased fibrosis, partly from titin-isoform shift. The titin-isoform shift may be beneficial for myocardial diastolic function, but could impair the contractile performance in systole.