Abstract
Rapid cooling contracture (RCC) was observed in frog toe muscles pretreated with caffeine, chlorpromazine (CPZ), or haloperidol (HPD). During rapid cooling contracture in the presence of caffeine (caffeine-RCC) tension developed to more than 0.8 of the maximum tetanic tension (P0). CPZ inhibited twitch but induced rapid cooling contracture (CPZ-RCC) between 50 and 150μM; the tension saturated at the level of 0.75 P0 at 100μM. HPD also inhibited twitch and induced rapid cooling contracture (HPD-RCC) at concentrations greater than 25 μM; the maximum tension was 0.25 P0. In the presence of dantrolene (10μM), the tension during CPZ-RCC was reduced by 40%. Procaine (0.25%) reduced the CPZ-RCC tension by as much as 60%. These results suggest that CPZ and HPD induced rapid cooling contracture by reducing Ca2+ -accumulation in sarcoplasmic reticulum.
