Malignant hyperthermia causing Gly2435Arg mutation of the ryanodine receptor facilitates ryanodine-induced calcium release in myotubes

We have investigated if cultivated muscle cells from malignant hyperthermia (MH) patients can be distinguished pharmacologically from controls. Muscle specimens from four individuals carrying the Gly2435Arg mutation of the skeletal muscle ryanodine receptor protein (RYRI) and from four controls were used to culture myotubes. Resting intracellular calcium concentration ([Ca²⁺](i)) of MH myotubes was similar to controls. However, when ryanodine 0.5 μmol litre^-1 was added, the kinetics of the increase in the calcium signals in MH and control cells were significantly different; the time for half maximum increase was mean 197 (SD 131) s for MH cells and 474 (61) s for controls (n = 80 cells each). On average, the area under the MH response curves was twice the control value. These results give rise to hopes that the phenotype of MH can be characterized using cultured human muscle and that a culture-based test for MH susceptibility may eventually be developed.