Functional characterization of malignant hyperthermia-associated RyR1 mutations in exon 44, using the human myotube model.

Malignant hyperthermia (MH) is a pharmacogenetic disorder with an autosomal dominant inheritance. During exposure to triggering agents as volatile anaesthetics, affected individuals may develop a potentially fatal hypermetabolic syndrome caused by excessive calcium release from the sarcoplasmic reticulum in skeletal muscle. More than 60 MH associated mutations were found in the gene of skeletal muscle ryanodine receptor (RyR1), but only some of them have been functionally characterized. Primary human myotubes were cultured from carriers of RyR1 mutations in exon 44 (Ala2350Thr, Arg2355Trp, Gly2375Ala) and from MH non-susceptible individuals. Investigation of calcium homeostasis with the calcium sensitive probe Fura 2 showed a higher sensitivity to the ryanodine receptor agonists 4-chloro-m-cresol, caffeine and halothane for the myotubes derived from the mutation carriers as compared to those of the control group. The presence of RyR1 mutations with impact on calcium homeostasis emphasizes the functional significance of exon 44.