Phenotyping malignant hyperthermia susceptibility by measuring halothane-induced changes in myoplasmic calcium concentration in cultured human skeletal muscle cells

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Abstract
Malignant hyperthermia (MH) is a potentially lethal disease triggered by volatile anaesthetics and succinylcholine in genetically predisposed individuals. Because of the heterogenetic nature of MH, a simple genetic-based diagnostic test is not feasible and diagnosis requires an invasive open muscle biopsy followed by the in vitro contracture test (IVCT). Our aim was to establish if measurements of halothane-induced increases in intracellular calcium ion concentration [Ca(2+)](i) in cultured human skeletal muscle cells can be used to phenotype MH susceptibility and if different mutations in the ryanodine receptor (RYR1) gene affect halothane-induced increases in [Ca(2+)](i). Primary cultures of human skeletal muscle cells were established from 54 individuals diagnosed by the IVCT according to the protocol of the European MH Group as: MH susceptible (n=22), MH negative (n=18) or MH equivocal (n=14). All individuals were screened for the presence of the most common mutations in the RYR1 gene. [Ca(2+)](i) was measured by fluorescent digital microscopy using fura-2/AM in 10 cells from each patient at five different halothane concentrations. The halothane-induced increase in [Ca(2+)](i) differed significantly between the three diagnostic groups. Different mutations of the RYR1 gene did not have a specific impact on halothane-induced increases in [Ca(2+)](i). Measurements of [Ca(2+)](i) in human skeletal muscle cells can be used to phenotype MH susceptibility; however, we did not observe a specific effect of any mutation in the RYR1 gene on the halothane-induced increase in [Ca(2+)](i).