Age-related functional effects linked to phosphatase activity in ventricular myocytes

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.

α-Tocopherol supplementation avoids apoptosis in the anal sphincter

PURPOSE

To analyze the influence of α-tocopherol supplementation on the levels of oxidative stress and apoptosis rates in the anal sphincter induced by orchiectomy in rats.

METHODS

Forty male Wistar rats weighing 250-300 g, were divided into four groups and sacrificed 8 weeks after: I- Control: sham; II- Orchiectomy: bilateral orchiectomy; III- Pre Orchiectomy Tocopherol: α-tocopherol supplementation for 4 weeks preceding bilateral orchiectomy; IV- Orchiectomy Full Tocopherol: α-tocopherol supplementation for 4 weeks before and 8 weeks after bilateral orchiectomy. The anal sphincter was analyzed stereologically to evaluate the density of collagen and the muscle fibers. The oxidative stress and the apoptosis were determined with 8-isprostane and caspase-3, respectively.

RESULTS

The collagen fibers concentration was statistically greater in Orchiectomy group than the others. The muscle fibers concentration was higher in Control and Orchiectomy Full Tocopherol than Orchiectomy and Pre Orchiectomy Tocopherol groups. Orchiectomy group showed higher 8-isoprostane concentrations compared to the other groups (p < 0.0003). Pre Orchiectomy Tocopherol and Orchiectomy Full Tocopherol groups presented caspase-3 levels lower than the Orchiectomy group (0.0072).

CONCLUSION

Vitamin supplementation with α-tocopherol for 12 weeks had the highest protection against bilateral orchiectomy generation of reactive oxygen species as well as apoptosis in the muscle fibers of the anal sphincter of rats.

Thin Filament Remodeling in Failing Myocardium

While the remodeling process in myocardial failure involves changes in ventricular structure and performance, it is now appreciated that it is also associated with changes in thin filament composition and function. As is discussed, changes at the level thick filament may affect thin filament activation in heart failure. Alterations in actin, troponin and tropomyosin isoform composition do not appear to be significant factors in human heart failure. In contrast, proteolytic degradation of troponin subunits are likely to be playing a functional role in some forms of cardiomyopathy (e.g. ischemic). Finally, phosphorylation of troponin I and troponin T by kinases (most notably protein kinase C) substantially affect thin filament function in failing human myocardium. These findings indicate that functional deficits in thin filament function in failing myocardium are largely reversible and create the potential for future targeted therapies in the treatment of this deadly disease.