Procaine enhancement of the rapid cooling contracture and inhibition of the decay of potentiated state in rabbit papillary muscle.

We tested the possibility that inhibition of Ca2+ release from the sarcoplasmic reticulum decreases the transsarcolemmal Ca2+ efflux and results in an increased sarcoplasmic reticulum Ca2+ content. We used procaine to inhibit sarcoplasmic reticulum Ca2+ release in rabbit papillary muscles. Rapid cooling-induced contractures were used as an index of sarcoplasmic reticulum Ca2+ content. Decay of potentiated state was measured to study whether the transsarcolemmal Ca2+ efflux is decreased in the presence of procaine. Procaine (0.5, 1.0 mM) inhibited contractions elicited by electrical stimulation and enhanced the rapid cooling-induced contracture. The initial decay of potentiated state that occurs when the muscle was stimulated at a low frequency was slowed in the presence of procaine. These results suggest that procaine inhibition of Ca(2+)-induced release of sarcoplasmic reticulum Ca2+ decreases the transsarcolemmal Ca2+ efflux relative to the influx, resulting in an increased sarcoplasmic reticulum Ca2+ content.