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 m ) 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 Ca2+-induced release of sarcoplasmic reticulum Ca2+decreases the transsarcolemmal Ca2+efflux relative to the influx, resulting in an increased sarcoplasmic reticulum Ca2+content.