SH oxidation coordinates subunits of rat brain ryanodine receptor channels activated by calcium and ATP

We have reported that ryanodine receptor (RyR) channels display three different responses to cytoplasmic free Ca2+ concentration ([Ca2+]) depending on their redox state (Marengo JJ, Hidalgo C, and Bull R. Biophys J 74: 1263-1277, 1998), with low, moderate, and high maximal fractional open times (P-o). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 muM cytoplasmic [Ca2+]. At 10 muM [Ca2+], low-P-o channels presented lower apparent affinity to activation by ATP [[ATP] for half-maximal activation (K-aATP) = 422 muM] than moderate-P-o channels (K-aATP = 82 muM). Oxidation of low-P-o channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-P-o channels and decreased K-aATP from 422 to 82 muM. At 0.1 muM cytoplasmic [Ca2+], ATP induced an almost negligible activation of low-P-o channels. After oxidation to high-P-o behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-P-o channels at 10 muM [Ca2+] plus ATP revealed the presence of subconductance states, suggesting a conduction mechanism that involves four independent subchannels. On oxidation the subchannels opened and closed in a concerted mode.