The role of aging on the control of contractile force by Na(+)-Ca2+ exchange in rat papillary muscle

Ventricular arrhythmias in acute myocardial ischaemia-Focus on the ageing and sex

Annually, approximately 17 million people die from cardiovascular diseases worldwide, half of them suddenly. The most common direct cause of sudden cardiac death is ventricular arrhythmia triggered by an acute coronary syndrome (ACS). The study summarizes the knowledge of the mechanisms of arrhythmia onset during ACS in humans and in animal models and factors that may influence the susceptibility to life-threatening arrhythmias during ACS with particular focus on the age and sex. The real impact of age and sex on the arrhythmic susceptibility within the setting of acute ischaemia is masked by the fact that ACSs result from coronary artery disease appearing with age much earlier among men than among women. However, results of researches show that in ageing process changes with potential pro-arrhythmic significance, such as increased fibrosis, cardiomyocyte hypertrophy, decrease number of gap junction channels, disturbances of the intracellular Ca²⁺ signalling or changes in electrophysiological parameters, occur independently of the development of cardiovascular diseases and are more severe in male individuals. A review of the literature also indicates a marked paucity of research in this area in female and elderly individuals. Greater awareness of sex differences in the aging process could help in the development of personalized prevention methods targeting potential pro-arrhythmic factors in patients of both sexes to reduce mortality during the acute phase of myocardial infarction. This is especially important in an era of aging populations in which women will predominate due to their longer lifespan.

Effect of age and sex on the incidence of ventricular arrhythmia in a rat model of acute ischemia

BACKGROUND

The impact of sex and age on the arrhythmic susceptibility within the setting of acute ischemia is masked by the fact that acute coronary events result from coronary artery disease appearing with age much earlier among men than among women.

METHODS AND RESULTS

LAD ligation or sham operations were performed in rats of both sexes at the age 3 and 24 months. An ECG was recorded continuously for 6 h after the operation. The number of early and late premature ventricular beats (PVBs), episodes of ventricular tachycardia (VT) and fibrillation (VF), heart rate, QRS, QT and Tpeak-Tend duration were analysed. Epicardial action potentials were recorded in vivo, Ca²⁺ signaling was evaluated in isolated cardiomyocytes, fibrosis and connexin-43 expression and localization were measured in the septum. PVBs, VT and VF episodes are much more common in older males than in young males and females independently from their age. Fibrosis with varying intensity in different muscle layers, hypertrophy of cardiomyocytes, reduced number of gap junctions and their appearance on the lateral myocyte membrane, QT prolongation, increase transmural dispersion of repolarisation and a decreased function of SERCA2a may increase the propensity to arrhythmia within the setting of acute ischemia.

CONCLUSION

We show that the male sex, especially in case of older individuals is a strong predictor of increased arrhythmic susceptibility within the acute ischemia setting regardless of its impact on the occurrence of cardiovascular diseases. A personalized sex-dependent prevention treatment is needed to reduce the mortality in acute phases of myocardial infarction.

How cardiomyocyte excitation, calcium release and contraction become altered with age

Cardiovascular disease is the main cause of death globally, accounting for over 17 million deaths each year. As the incidence of cardiovascular disease rises markedly with age, the overall risk of cardiovascular disease is expected to increase dramatically with the aging of the population such that by 2030 it could account for over 23 million deaths per year. It is therefore vitally important to understand how the heart remodels in response to normal aging for at least two reasons: i) to understand why the aged heart is increasingly susceptible to disease; and ii) since it may be possible to modify treatment of disease in older adults if the underlying substrate upon which the disease first develops is fully understood. It is well known that age modulates cardiac function at the level of the individual cardiomyocyte. Generally, in males, aging reduces cell shortening, which is associated with a decrease in the amplitude of the systolic Ca(2+) transient. This may arise due to a decrease in peak L-type Ca(2+) current. Sarcoplasmic reticulum (SR) Ca(2+) load appears to be maintained during normal aging but evidence suggests that SR function is disrupted, such that the rate of sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA)-mediated Ca(2+) removal is reduced and the properties of SR Ca(2+) release in terms of Ca(2+) sparks are altered. Interestingly, Ca(2+) handling is modulated by age to a lesser degree in females. Here we review how cellular contraction is altered as a result of the aging process by considering expression levels and functional properties of key proteins involved in controlling intracellular Ca(2+). We consider how changes in both electrical properties and intracellular Ca(2+) handling may interact to modulate cardiomyocyte contraction. We also reflect on why cardiovascular risk may differ between the sexes by highlighting sex-specific variation in the age-associated remodeling process. This article is part of a Special Issue entitled CV Aging.

Molecular mechanisms of cardiomyocyte aging

Western societies are rapidly aging, and cardiovascular diseases are the leading cause of death. In fact, age and cardiovascular diseases are positively correlated, and disease syndromes affecting the heart reach epidemic proportions in the very old. Genetic variations and molecular adaptations are the primary contributors to the onset of cardiovascular disease; however, molecular links between age and heart syndromes are complex and involve much more than the passage of time. Changes in CM (cardiomyocyte) structure and function occur with age and precede anatomical and functional changes in the heart. Concomitant with or preceding some of these cellular changes are alterations in gene expression often linked to signalling cascades that may lead to a loss of CMs or reduced function. An understanding of the intrinsic molecular mechanisms underlying these cascading events has been instrumental in forming our current understanding of how CMs adapt with age. In the present review, we describe the molecular mechanisms underlying CM aging and how these changes may contribute to the development of cardiovascular diseases.

Modulation of sarcoplasmic reticulum Ca(2+) cycling in systolic and diastolic heart failure associated with aging

Hypertension, atherosclerosis, and resultant chronic heart failure (HF) reach epidemic proportions among older persons, and the clinical manifestations and the prognoses of these worsen with increasing age. Thus, age per se is the major risk factor for cardiovascular disease. Changes in cardiac cell phenotype that occur with normal aging, as well as in HF associated with aging, include deficits in ss-adrenergic receptor (ss-AR) signaling, increased generation of reactive oxygen species (ROS), and altered excitation-contraction (EC) coupling that involves prolongation of the action potential (AP), intracellular Ca(2+) (Ca(i)(2+)) transient and contraction, and blunted force- and relaxation-frequency responses. Evidence suggests that altered sarcoplasmic reticulum (SR) Ca(2+) uptake, storage, and release play central role in these changes, which also involve sarcolemmal L-type Ca(2+) channel (LCC), Na(+)-Ca(2+) exchanger (NCX), and K(+) channels. We review the age-associated changes in the expression and function of Ca(2+) transporting proteins, and functional consequences of these changes at the cardiac myocyte and organ levels. We also review sexual dimorphism and self-renewal of the heart in the context of cardiac aging and HF.

Age and hypertrophy related changes in contractile post-rest behavior and action potential properties in isolated rat myocytes

"Physiological" aging as well as early and progressive cardiac hypertrophy may affect action potential (AP) pattern, contractile function, and Ca(2+) handling. We hypothesize that contractile function is disturbed in hypertrophy from early stages and is differently affected in aged myocardium. In vivo function, cardiomyocyte contractile behavior and APs were compared in Wistar-Kyoto (WIS) rats and spontaneously hypertensive rats (SHR) at different ages and degrees of hypertrophy (3-4, 9-11, 20-24 months). Post-rest (PR) behavior was used to investigate the relative contribution of the sarcoplasmic reticulum (SR) and the Na/Ca exchanger (NCX) to cytosolic Ca(2+) removal. APs were recorded by whole-cell current-clamp and sarcomere shortening by video microscopy. Cyclopiazonic acid was used to suppress Ca(2+) ATPase (SERCA) function. Heart weight/body weight ratio was increased in SHR versus WIS within all age groups. Myocyte steady state (SS) shortening amplitude was reduced in young SHR versus WIS. Aging led to a significant decay of SS contractile amplitude and relengthening velocity in WIS, but the PR potentiation was maintained. In contrast, aging in SHR led to a decrease of PR potentiation, while SS contraction and relengthening velocity increased. APD(50%) was always prolonged in SHR versus WIS. With aging, APD(50%) increased in both WIS and SHR, but was still shorter in WIS. However, in old WIS the late AP portion (APD(90%)) was prolonged. Ca(2+) handling and AP properties are disturbed progressively with aging and with increasing hypertrophy. Decreased amplitude of shortening and velocity of relengthening in aged WIS may be attributed to reduced SERCA function. In SHR, an increase in SR leak and shift towards transmembraneous Ca handling via NCX may be responsible for the changes in contractile function. A prolonged APD(90%) in aged WIS may be an adaptive mechanism to preserve basal contractility. Therefore, the effects on contractile parameters and AP are different in hypertrophy and aging.

Influence of age and run training on cardiac Na+/Ca2+ exchange

Effects of age and training on myocardial Na+/Ca2+ exchange were examined in young sedentary (YS; 14-15 mo), aged sedentary (AS; 27-31 mo), and aged trained (AT; 8- to 11-wk treadmill run training) male Fischer Brown Norway rats. Whole heart performance and isolated cardiocyte Na+/Ca2+ exchange characteristics were measured. At the whole heart level, a small but significant slowing of late isovolumic left ventricular (LV) relaxation, which may be indicative of altered Na+/Ca2+ exchange activity, was seen in hearts from AS rats. This subtle impairment in relaxation was not observed in hearts from AT rats. At the single-cardiocyte level, late action potential duration was prolonged, resting membrane potential was more positive, and overshoot potential was greater in cardiocytes from AS rats than from YS rats (P < 0.05). Training did not influence any of these age-related action potential characteristics. In electrically paced cardiocytes, neither shortening nor intracellular Ca2+ concentration ([Ca2+]i) dynamics was influenced by age or training. Similarly, neither age nor training influenced the rate of [Ca2+]i clearance via forward (Nain+ /Caout2+) Na+/Ca2+ exchange after caffeine-induced Ca2+ release from the sarcoplasmic reticulum or cardiac Na+/Ca2+ exchanger protein (NCX1) expression. However, when whole cell patch-clamp techniques combined with fluorescence microscopy were used to evaluate the ability of Na+/Ca2+ exchange to alter cytosolic [Ca2+] ([Ca2+]c) under conditions where membrane potential (Vm) and internal and external [Na+] and [Ca2+] could be controlled, we observed age-associated increases in forward Na+/Ca2+ exchange-mediated [Ca2+]c clearance (P < 0.05) that were not influenced by training. The age-related increase in forward Na+/Ca2+ exchange activity provides a hypothetical explanation for the late action potential prolongation observed in this study.

Effects of melatonin in isolated rat papillary muscle

Melatonin (N-acetyl-5-methoxytryptamine), the principal hormone of the vertebral pineal gland, elicits several neurobiological effects. However, the effects of melatonin on cardiac muscle are still unknown. The first goal of the study was to investigate the role of melatonin on myocardial contractility in isolated rat papillary muscle using dose-response curves to melatonin, to isoproterenol and calcium either in the presence or in the absence of melatonin (0.3 nM). Response curves to isoproterenol were additionally performed in the presence of melatonin plus the specific receptor antagonist N-acetyltryptamine (10 microM); the adenylate-cyclase stimulator forskolin (10 microM) was also used. Melatonin has no direct inotropic effect in isolated rat papillary muscle but counteracts isoproterenol but not [Ca2+] effects. In fact, the EC50 for isoproterenol was significantly higher in the presence than in the absence of melatonin (p < 0.001). This anti-adrenergic action occurs through an interaction to a specific cardiac receptor. Forskolin-stimulated adenylate cyclase induced an increase of contractile force (+118 +/- 25%) which was reduced in the presence of melatonin (+26 +/- 10%; p < 0.01). In conclusion, we found that melatonin possess anti-adrenergic effect in isolated rat papillary muscle. This phenomenon was abolished in the presence of its receptor antagonist N-acetyl-tryptamine demonstrating that melatonin operates through a specific cardiac receptor. The reduction of contractility increase, induced by forskolin-stimulated adenylate cyclase, shows that melatonin may act through a reduction of cyclic AMP accumulation.