In vitro muscle contractures induced by halothane and suxamethonium. I: The rat diaphragm.

The rat diaphragm was used as an in vitro model for studies of contractures synergistically-induced by halothane and suxamethonium. The effects of three agents reported to inhibit phospholipase A2 activity (quinacrine, spermine and indomethacin), tubocurarine and dantrolene were examined on these contractures. Contractures induced by 1% halothane (0.26 +/- 0.02 g) (mean +/- SEM) were increased (0.60 +/- 0.04 g) if suxamethonium 50 mmol litre-1 was also in the bathing medium. Suxamethonium-induced contractures (0.22 +/- 0.03 g) were also enhanced when halothane was present (0.51 +/- 0.03 g). Spermine, indomethacin and dantrolene antagonized both halothane- and suxamethonium-induced contractures. Quinacrine potentiated contractures induced by either halothane or suxamethonium. Contractures induced by suxamethonium were antagonized by tubocurarine; however, contractures induced by halothane were not antagonized by tubocurarine. These results suggest that free fatty acids may be involved in contractures induced synergistically by halothane and suxamethonium. Different mechanisms are involved in the induction of contractures by suxamethonium than by halothane.