Postulated role of interdomain interaction between regions 1 and 2 within type 1 ryanodine receptor in the pathogenesis of porcine malignant hyperthermia

We have demonstrated recently that CICR (Ca 2+ -induced Ca 2+ release) activity of RyRI (ryanodine receptor 1) is held to a low level in mammalian skeletal muscle ('suppression' of the channel) and that this is largely caused by the interdomain interaction within RyR1 [Murayama, Oba, Kobayashi, Ikemoto and Ogawa (2005) Am. J. Physiol. Cell Physiol. 288, C1222-C1230]. To test the hypothesis that aberration of this suppression mechanism is involved in the development of channel dysfunctions in MH (malignant hyperthermia), we investigated properties of the RyRI I channels from normal and MHS (MH-susceptible) pig skeletal muscles with an Arg615 -> Cys mutation using [ 3 H]ryanodine binding, single-channel recordings and SR (sarcoplasmic reticulum) Ca 2+ release. The RyR1 channels from MHS muscle (RyRI MHS ) showed enhanced CICR activity compared with those from the normal muscle (RyRI N ), although there was little or no difference in the sensitivity to several ligands tested (Ca 2+ , Mg 2+ and adenine nucleotide), nor in the FKBP12 (FK506-binding protein 12) regulation. DP4, a domain peptide matching the Leu 2442 -Pro 2477 region of RyRi which was reported to activate the Ca 2+ channel by weakening the interdomain interaction, activated the RyRI N channel in a concentration-dependent manner, and the highest activity of the affected channel reached a level comparable with that of the RyRI MHS channel with no added peptide. The addition of DP4 to the RyRI MHS channel produced virtually no further effect on the channel activity. These results suggest that stimulation of the RyRI MHS channel caused by affected interdomain interaction between regions 1 and 2 is an underlying mechanism for dysfunction of Ca 2+ homoeostasis seen in the MH phenotype.