ACTION OF HALOTHANE ON RAT SOLEUS MUSCLE: TEMPERATURE DEPENDENT INDUCTION OF CONTRACTURES AND MODIFICATION OF CAFFEINE AND POTASSIUM CONTRACTURES

Halothane induced calcium-dependent contractures in rat soleus muscle at temperatures between 4°C and 13°C, but not at higher temperatures. The peak tension of the contractures increased as temperature was decreased below 13°C. The magnitudes of the contractures were reduced by the addition of cobalt or lanthanum ions to the medium in the water bath. The anaesthetic also potentiated caffeine-induced contractures in muscle at 22° C and 37°C in a calcium-dependent manner. The contractures at 37°C were more sensitive to the concentration of this ion than were contractures at 22°C. Halothane increased peak tension and prolonged the time course of potassium-induced contractures, but did not alter their threshold values at either 22°C or 37°C. It was concluded that, in rat muscle, halothane may act at a site on the plasmamalemma, retard the onset of inactivation and move the inactivation curve further from the resting membrane potential.