COMPARATIVE-STUDIES ON THE INDUCTION OF MUSCLE CONTRACTURE IN MOUSE DIAPHRAGM AND CA2-RETICULUM VESICLES BY ORGANOTIN COMPOUNDS( RELEASE FROM SARCOPLASMIC)

Effects of organotins, including triethyltin and tributyltin, on skele tal muscle were studied with diaphragm and isolated sarcoplasmic retic ulum membrane vesicles. Triethyltin induced muscle contracture in mous e diaphragm while tributyltin had comparatively less potency and effic acy in inducing the muscle contracture. The contracture induced by tri butyltin was inhibited when the diaphragm was pretreated with low Ca2 medium or caffeine while the contracture induced by triethyltin persi sted in the Ca2+ free medium but was inhibited by pretreatment of caff eine. Pretreatment of dithiothreitol blocked the contracture induced b y tributyltin but not that by triethyltin. Triethyltin dose-dependentl y induced Ca2+ release From sarcoplasmic reticulum vesicles and inhibi ted the Ca2+-ATPase activity. These results suggested that triethyltin induced contracture in mouse diaphragm was mainly by induction of Ca2 + release and inhibition of Ca2+ uptake of the internal Ca2+ storage s ite the sarcoplasmic reticulum, while the tributyltin induced contract ure might be due to enhancement of extracellular Ca2+ influx which fur ther induce the release of internal Ca2+ through the Ca2+ induced Ca2 release mechanism.