CAPSAICIN DOES NOT INHIBIT THE INTRACELLULAR CALCIUM HANDLING PROCESSIN RAT VENTRICULAR PAPILLARY-MUSCLE

1. We studied the effects of capsaicin, a pungent agent extracted from red pepper, on rested-state contraction (RSC) of isolated rat ventric ular 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 mus cle 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, caffe ine 10(-2) M or ryanodine 10(-7) M, respectively. 4. All drugs inhibit ed 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 intrac ellular Ca2+ store in rat cardiac muscle.