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 (Ca2+-induced Ca2+ release) activity of RyR1 (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 RyR1 channels from normal and MHS (MH-susceptible) pig skeletal muscles with an Arg(615) -> CyS mutation using [H-3]ryanodine binding, single-channel recordings and SR (sarcoplasmic reticulum) Ca2+ release. The RyR1 channels from MHS muscle (RyR1 MHS) showed enhanced CICR activity compared with those from the normal muscle (RyR1(N)), although there was little or no difference in the sensitivity to several ligands tested (Ca2+, Mg2+ and adenine nucleotide), nor in the FKBP 12 (FK506-binding protein 12) regulation. DP4, a domain peptide matching the Leu(2442)-Pro(2477) region of RyR1 which was reported to activate the Ca2+ channel by weakening the interdomain interaction, activated the RyR1(N), channel in a concentration-dependent manner, and the highest activity of the affected channel reached a level comparable with that of the RyR1(MHS) channel with no added peptide. The addition of DP4 to the RyR1(MHS,) channel produced virtually no further effect on the channel activity. These results suggest that stimulation of the RyR1(MHS) channel caused by affected interdomain interaction between regions I and 2 is an underlying mechanism for dysfunction of Ca2+ homoeostasis seen in the MH phenotype.