Dantrolene blocks the tonic contraction and calcium influx evoked by K + in real longitudinal smooth muscle

Abstract

1. 1. Dantrolene (10 −8-10 −4M) reduced the K + (60 mM) tonic response in accordance with decreased Ca 2+ uptake, as determined by La method, more than the phasic in ileal muscle. 2. 2. After saponin-treatment of the fibers, which leaves the Ca 2+ storage sites intact, dantrolene had only a slight effect on the caffeine-induced contraction. In Triton-X-100-treated fibers, in which the Ca 2+ release sites are destroyed, dantrolene did not affect the Ca 2+-induced contraction. 3. 3. The results suggest that dantrolene inhibited the high-K +-induced tonic response mainly by inhibiting Ca 2+ influx via voltage-dependent Ca 2+ channels in ileum without affecting contractile elements. In contrast, dantrolene had only a slight effect on the intracellular Ca 2+ release from caffeine-sensitive release sites.