Dantrolene suppresses spontaneous Ca~(2+) release without altering excitation-contraction coupling in cardiomyocytes of aged mice

摘要

Cardiac dysfunction in the aged heart reflects abnormalities in cardiomyocyte Ca~(2+) homeostasis including altered Ca~(2+) cycling through the sarco-plasmic reticulum (SR). The ryanodine receptor antagonist dantrolene exerts antiarrhythmic effects by preventing spontaneous diastolic Ca~(2+) release from the SR. We tested the hypothesis that dantrolene prevents spontaneous Ca~(2+) release without altering excitation-contraction coupling in aged myocardium. Left ventricular cardiomyocytes isolated from young (3 to 4 mo) and aged (24-26 mo) C57BL/6 mice were loaded with the Ca~(2+) indicator fluo-4. Amplitudes of action potential-induced Ca~(2+) transients at 1-Hz pacing were similar between young and aged mice, yet cell shortening was impaired in aged mice. Isoproterenol (1 muM) increased Ca~(2+) transient amplitude and cell shortening to identical levels in young and aged; dantrolene (1 muM) had no effect on Ca~(2+) transients or cell shortening during pacing. Under Ca~(2+) overload conditions induced with 10 mM extracellular Ca~(2+) concentration, spontaneous Ca~(2+) waves were of diminished amplitude and associated with lower SR Ca~(2+) content in aged versus young mice. Despite no effect in young mice, dantrolene increased SR Ca~(2+) content and Ca~(2+) wave amplitude in aged mice. In the presence of isoproterenol following rest from 1-Hz pacing, Ca~(2+) spark frequency was elevated in aged mice, yet the time to spontaneous Ca~(2+) wave was similar between young and aged mice; dantrolene decreased Ca~(2+) spark frequency and prolonged the time to Ca~(2+) wave onset in aged mice with no effect in young mice. Thus dantrolene attenuates diastolic Ca~(2+) release in the aged murine heart that may prove useful in preventing cardiac dysfunction.