The caffeine/halothane contracture test in North America and the in vitro contracture test in Europe are currently the only validated bioassays for diagnosing malignant hyperthermia susceptibility and phenotyping families. Both tests are invasive requiring surgical muscle biopsy. Here, we report first use of the selective ryanodine receptor type I agonist ryanodine in a percutaneous microdialysis protocol designed to test whether microdialysis-induced local metabolic responses of skeletal muscle due to ryanodine receptor activation can differentiate between malignant hyperthermia-sensitive and normal pigs.

Six microdialysis catheters were implanted percutaneously into the adductor muscles of the right and left thighs of malignant hyperthermia-susceptible (n = 9) and normal (n = 8) anaesthetized (ketamine/propofol) and mechanically ventilated swine. Systemic blood gases, haemodynamic parameters and creatine kinase levels were measured before, during and after microdialysis perfusion of ryanodine. After a post-implantation equilibration period of 30 min, one catheter perfused (2 μL min−1) with 0.9% NaCl (control) and was compared with the remaining five catheters perfused with increasing concentrations of ryanodine (0.2–100 μmol). Lactate and pyruvate levels were measured enzymatically.

Continuous perfusion with ryanodine revealed dose-dependent sigmoidal increases in the dialysate lactate and lactate–pyruvate ratio parameters; these effects were greatly augmented in malignant hyperthermia-susceptible pigs compared to normal pigs (two- to threefold): estimated EC50 greatly decreased (>19-fold) while the maximum effect increased (>twofold) in the malignant hyperthermia-susceptible group.

The in vivo percutaneous microdialysis protocol for skeletal muscle, using ryanodine as the ryanodine receptor type I agonist and dialysed lactate–pyruvate parameters as metabolic index, can reproducibly differentiate between malignant hyperthermia-susceptible and normal swine.