APPS November 2002 Meeting Abstract 2411

Esther M. Gallant, Suzanne Curtis, James Hart, Kevin Eager, Angela F. Dulhunty, Division of Molecular Biosciences, John Curtin School of Medical Research, Australian National University, Canberra, ACT, and Department of Veterinary PathoBioloigy, University of Minnesota, Saint Paul, MN, USA.

Skeletal muscle from pigs and humans susceptible to malignant hyperthermia (MH) is more sensitive than normal muscle to caffeine - induced contractures. This sensitivity to caffeine is widely used as part of the testing procedure for diagnosis of MH susceptibility in humans and experimentally in pigs. It is therefore somewhat puzzling that purified ryanodine-receptor (RYR1) calcium release channels isolated from MH-susceptible (MHS) porcine skeletal muscle are reported not to exhibit this enhanced sensitivity⁽¹⁾. We have used native normal and porcine MHS RYR1s incorporated into lipid bilayers to evaluate the effect of caffeine on the single channel currents at +40 mV and -40 mV test potentials with cesium as the current carrier. We found that the caffeine dose response curve was shifted leftward for MHS as compared to normal RYR1s at both test voltages. However, the effect was most marked at -40 mV with current moving in the physiological direction from sarcoplasmic reticulum lumen to cytoplasm. At 1 mM caffeine the mean current of MHS RYR1s was increased by approximately 14-fold at +40 mV but only by approximately 4-fold at -40mV. There was no significant increase in mean current of the normal RYR1s by 1 mM caffeine at either voltage. Possibly the enhanced caffeine sensitivity of the MHS RYR requires the presence of a co-protein or modifying factor that is removed in the purification process. If so, this would explain the difference in our results and those of previous studies using purified RYR1s which might have lacked these additional factors.⁽¹⁾