Rapid cooling contractures in rat skinned myocardium: effects of isoflurane and halothane

Rapid cooling contractures (RCCs) have been elicited in rat ventricular cardiac muscle skinned by saponin (50 micrograms/ml). The size and shape of the RCC in skinned cardiac muscle were similar to those observed in intact cardiac muscle. The ATP-dependent Ca2-uptake pump in the sarcoplasmic reticulum (SR) was active at low temperature and could efficiently load the SR with Ca2+ even at 3 degrees C. Halothane reduced both RCC and caffeine contracture in a dose-dependent way when halothane treatment was applied before either RCC or caffeine. This action is consistent with halothane-induced depletion of the SR Ca2+. Under similar conditions, isoflurane inhibited RCC but had little effect on the caffeine contracture. This may suggest that rapid cooling and caffeine have different modes of action on the SR Ca(2+)-release channel. Our results provide further strong supporting evidence for differential inhibitory actions on a key intracellular organelle in cardiac muscle by two vapor anesthetic agents.