IN-VITRO DIAGNOSIS OF MALIGNANT HYPERTHERMIA SUSCEPTIBILITY WITH RYANODINE-INDUCED CONTRACTURES IN HUMAN SKELETAL-MUSCLES

The in vitro contracture test with ryanodine is a new method to distin guish malignant hyperthermia (MH) susceptible (MHS) from normal (MHN) patients. The purpose of our investigation was to determine whether sm aller concentrations of ryanodine than those used previously may resul t in a better differentiation. We performed a ryanodine contracture te st (RCT) using concentrations of 1 and 2 mu M in muscle specimens of 4 1 MHS, 58 MHN, and 19 MH-equivocal (MHE) patients. Nine patients were excluded from the study due to neuromuscular diseases. All contracture levels (i.e., start of contractures, contractures of 0.2 g and 1.0 g) were attained significantly earlier in MHS than in MHN muscles at bot h concentrations of ryanodine. Using a ryanodine concentration of 2 mu M, all contracture levels were reached significantly faster than with 1 mu M. There was no overlap in the range of times between groups at all contracture levels with ryanodine 1 and 2 mu M. The median thresho ld times for all MHE patients were always between those of MHS and MHN . Defining arbitrarily threshold times for MHS and ME-IN, an assignmen t of MHE patients to either MHS or MHN using 1 or 2 mu M ryanodine was possible in most cases. Ryanodine administration at a concentration o f 1 mu M led to a better distinction of MHS from MHN patients than 2 m u M, The RCT with ryanodine 1 mu M should therefore be added to the cu rrent diagnostic methods.