SH oxidation coordinates subunits of rat brain ryanodine receptor channels activated by calcium and ATP |
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Authors: | Bull Ricardo Marengo Juan José Finkelstein José Pablo Behrens María Isabel Alvarez Osvaldo |
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Institution: | Programa de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Santiago 838-0453, Chile. |
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Abstract: | 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: 12631277, 1998), with low, moderate, and high maximal fractional open times (Po). Activation by ATP of single RyR channels from rat brain cortex was tested in planar lipid bilayers with 10 or 0.1 µM cytoplasmic Ca2+]. At 10 µM Ca2+], low-Po channels presented lower apparent affinity to activation by ATP ATP] for half-maximal activation (KaATP) = 422 µM] than moderate-Po channels (KaATP = 82 µM). Oxidation of low-Po channels with thimerosal or 2,2'-dithiodipyridine (DTDP) gave rise to moderate-Po channels and decreased KaATP from 422 to 82 µM. At 0.1 µM cytoplasmic Ca2+], ATP induced an almost negligible activation of low-Po channels. After oxidation to high-Po behavior, activation by ATP was markedly increased. Noise analysis of single-channel fluctuations of low-Po channels at 10 µM 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. subconductance states; calcium ion release channels; calcium ion regulation; thimerosal; 2,2'-dithiodipyridine |
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