In vitro interaction between halothane and succinylcholine in human skeletal muscle: implications for malignant hyperthermia and masseter muscle rigidity.

This study examines in vitro the contractures induced by halothane and succinylcholine in skeletal muscle taken as biopsy specimens from 42 patients referred to the authors' laboratory for diagnosis of malignant hyperthermia (MH) susceptibility. In addition, possible differences between the response of preparations from these same patients with and without a history of masseter muscle rigidity following succinylcholine (SCh) administration were determined to investigate the in vitro relationship of masseter muscle rigidity to MH. Halothane 3%-induced contractures in preparations from MH susceptibles were similar, whether the group had a history of masseter muscle rigidity (1.15 +/- 0.18 g; n = 10) or not (1.02 +/- 0.21 g; n = 14). Halothane did not induce significant contractures in those diagnosed as normals. Succinylcholine alone did not elicit contractures from preparations derived from MH susceptibles or nonsusceptibles. Succinylcholine induced significant contractures in all preparations preexposed to halothane. Preparations from MH-negative patients with a history of masseter muscle rigidity were rendered sensitive to halothane (contractures of 1.17 +/- 0.30 g; n = 4) when SCh was present. In contrast, halothane added in the presence of SCh did not induce contractures to the same extent in preparations from MH-negative patients without a history of masseter muscle rigidity. This is the first reported in vitro method by which to examine the clinically troublesome interaction between SCh and halothane. This approach also may prove to be important in further investigations of the relationship between masseter muscle rigidity and MH.