Dantrolene Prevents Spontaneous Calcium Waves in Cardiac Myocytes from Aged Mice

Abstract

Contractile dysfunction in the aged heart reflects abnormalities in intracellular cycling of Ca through the sarcoplasmic reticulum (SR). Dantrolene exerts antiarrhythmic effects on cardiac myocytes from animal models of heart failure, presumably by preventing spontaneous diastolic Ca release through ryanodine receptor channels. In this study we tested the hypothesis that dantrolene prevents diastolic Ca release in the Aged myocardium. Left-ventricular myocytes isolated from Young (3-4 month) and Aged (24-26 month) C57BL/6 male mice were loaded with the Ca indicator fluo-4/AM and exposed to elevated extracellular Ca (10 mM) to induce spontaneous Ca waves. Ca waves were observed at similar frequencies in Aged (10.2 ± 1.7 waves/min) and Young (8.7 ± 2.7 waves/min), yet waves in Aged were of smaller amplitude (F/Fo = 3.9 ± 0.5 Aged versus 6.0 ± 0.3 Young, P<0.05) and occurred at a lower threshold SR Ca content as assessed by application of 10 mM caffeine (F/Fo,Caffeine= 4.8 ± 0.4 Aged versus 7.4 ± 0.2 Young, P<0.05). Dantrolene treatment (1 μM, 5 min) in Aged decreased wave frequency (to 7.3 ± 1.7 waves/min, P<0.05), increased wave amplitude (to F/Fo= 5.0 ± 0.5, P<0.05), and increased threshold SR Ca content (to F/Fo,Caffeine= 6.1 ± 0.4, P<0.05) but had no effect in Young. Dantrolene had no effect on the amplitude of action-potential induced Ca transients (0.5 Hz, 2 mM extracellular Ca) in Aged or Young. Thus, dantrolene can have beneficial effects on Ca cycling in Aged cardiomyocytes which may prove useful in treating cardiac dysfunction commonly associated with advancing age. (Support: NIH K01AG041208, RO1HL086483).