Age-dependent variation in contractility of adult cardiac myocytes.

This study was designed to examine the influence of the age of adults on the contractile characteristics of the myocardium and to ascertain whether the age dependent variation is related to variation in sarcolemmal calcium channels. Cardiomyocytes were isolated from 2, 6 and 12-month-old, male Sprague-Dawley rats and the extent and velocity of contraction were recorded as a function of change in cell length. Age dependent increase in cell length and sarcomere length was significant (P<0.05). Extent of contraction increased with age and the velocities of contraction and relaxation normalized to total contraction decreased with age (P<0.05). Sensitivity to the L-type channel antagonist (verapamil, 1 microM) and the T-type channel antagonist (nickel chloride, 40 microM) was significant in 6 and 12-month-old animals. This differential response to calcium channel antagonists suggests that the age-dependent variation in contractility may be mediated by the variation in the distribution/function of sarcolemmal calcium channels.