DANTROLENE BLOCKS THE TONIC CONTRACTION AND CALCIUM INFLUX EVOKED BY K-MUSCLE( IN ILEAL LONGITUDINAL SMOOTH)

1. Dantrolene (10(-5)-10(-4) M) reduced the K+ (60 mM) tonic response in accordance with decreased Ca2+ uptake, as determined by La method, more than the phasic in ileal muscle. 2. After saponin treatment of th e fibers, which leaves the Ca2+ storage sites intact, dantrolene had o nly a slight effect on the caffeine induced contraction. In Triton X-1 00-treated fibers, in which the Ca2+ release sites are destroyed, dant rolene did not affect the Ca2+ induced contraction, 3. The results sug gest that dantrolene inhibited the high-K+-induced tonic response main ly by inhibiting Ca2+ influx via voltage dependent Ca2+ channels in il eum without affecting contractile elements. In contrast, dantrolene ha d only a slight effect on the intracellular Ca2+ release from caffeine sensitive release sites.