Comparative studies on the induction of muscle contracture in mouse diaphragm and Ca²⁺ release from sarcoplasmic reticulum vesicles by organotin compounds

Effects of organotins, including triethyltin and tributyltin, on skeletal muscle were studied with diaphragm and isolated sarcoplasmic reticulum membrane vesicles. Triethyltin induced muscle contracture in mouse diaphragm while tributyltin had comparatively less potency and efficacy in inducing the muscle contracture. The contracture induced by tributyltin was inhibited when the diaphragm was pretreated with low Ca²⁺ medium or caffeine while the contracture induced by triethyltin persisted in the Ca²⁺-free medium but was inhibited by pretreatment of caffeine. Pretreatment of dithiothreitol blocked the contracture induced by tributyltin but not that by triethyltin. Triethyltin dose-dependently induced Ca²⁺ release from sarcoplasmic reticulum vesicles and inhibited 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 site the sarcoplasmic reticulum, while the tributyltin induced contracture might be due to enhancement of extracellular Ca²⁺ influx which further induce the release of internal Ca²⁺ through the Ca²⁺induced Ca²⁺ release mechanism.