1. We studied the effects of capsaicin, a pungent agent extracted from red pepper, on rested-state contraction (RSC) of isolated rat ventricular papillary muscles.
2. The RSC was induced by stimulation, after a rest interval of 5 sec to 10 min, after the twitch tension of the muscle preparation stimulated at the regular stimulus frequency of cycle lengths of 5, 1 or 0.2 sec attained the steady state.
3. Drug effects were evaluated on the RSC in the presence of capsaicin 10(-5) M, caffeine 10(-2) M or ryanodine 10(-7) M, respectively.
4. All drugs inhibited the RSC but to different degrees, Ryanodine was the most effective in inhibiting RSC, followed by caffeine and capsaicin, in that order. However, the inhibitory mode varied, depending on the drugs.
5. These findings suggest that capsaicin may not inhibit the function of intracellular Ca2+ store in rat cardiac muscle.
