RAPID COOLING CONTRACTURES IN RAT SKINNED MYOCARDIUM - EFFECTS OF ISOFLURANE AND HALOTHANE

Rapid cooling contractures (RCCs) have been elicited in rat ventricula r cardiac muscle shinned by saponin (50 mu g/ml). The size and shape o f the RCC in skinned cardiac muscle were similar to those observed in intact cardiac muscle. The ATP-dependent Ca2+ uptake pump in the sarco plasmic reticulum (SR) was active at low temperature and could efficie ntly load the SR with Ca2+ even at 3 degrees C. Halothane reduced both RCC and caffeine contracture in a dose-dependent way when halothane t reatment was applied before either RCC or caffeine. This action is con sistent with halothane-induced depletion of the SR Ca2+. Under similar conditions, isoflurane inhibited RCC but had little effect on the caf feine contracture. This may suggest that rapid cooling and caffeine ha ve different modes of action on the SR Ca2+-release channel. Our resul ts provide further strong supporting evidence for differential inhibit ory actions on a key intracellular organelle in cardiac muscle by two vapor anesthetic agents.