Ion channel gating in cardiac ryanodine receptors from the arrhythmic RyR2-P2328S mouse

Abstract

Mutations in the cardiac ryanodine receptor calcium release channel (RyR2) can cause deadly ventricular arrhythmias and atrial fibrillation (AF). The RyR2-P2328S mutation produces catecholaminergic polymorphic ventricular tachycardia (CPVT) and AF in hearts from RyR2P2328S/P2328S (RyR2S/S) mice. We have now examined P2328S RyR2 channels from RyR2S/S hearts. The activity of wild type (WT) and P2328S RyR2 channels was similar at a cytoplasmic [Ca2+] of 1 mM, but P2328S RyR2 was significantly more active than WT at a cytoplasmic [Ca2+] of 1 µM. This was associated with a >10-fold shift in the AC50 for Ca2+-activation from ∼3.5 µM Ca2+ in WT RyR2 to ∼320 nM in P2328S channels and an unexpected >1000-fold shift in the IC50 for inactivation from ∼50 mM in WT channels to ≤7 µM in P2328S channels, into systolic [Ca2+] levels. Unexpectedly, the shift in Ca2+-activation was not associated with changes in subconductance activity, S2806 or S2814 phosphorylation, or FKBP12 bound to the channels. The changes in channel activity with the P2328S mutation correlate with altered Ca2+ homeostasis in myocytes from RyR2S/S mice and the CPVT and AF phenotypes.