[Effect of calcium on the force-frequency ratio and resting potentiation in the myocardium of mature and old rats].

The studies on the isolated papillary muscles have shown age-dependent differences in the tension developed, the rate of its development and decline in adult (10 months) and old (27 months) rats at 0.1 Hz stimulation frequency and different concentrations of external calcium (0.3, 1.25, 5.0). With 0.3 mM of Ca2+ in the solution, the negative inotropic frequency effect, and resting potentiation of contractions (interstimulus interval 30 s) in the myocardium of old rats were considerably lower than those in adult animals. Calcium level elevation (5.0 mM) resulted in elimination of frequency inotropic effect and resting potentiation in the rat myocardium in both age groups. The abnormalities of chronoinotropic relations in the myocardium during aging can probably be explained by the changes in Ca2+ transport.