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1 Programa de Fisiologia y Biofisica, Universidad de Chile, Facultad de Medicina, Instituto de Ciencias Biomedicas, Santiago, Chile
2 Programa de Fisiologia y Biofisica, Universidad de Chile, Facultad de Medicina, Instituto de Ciencias Biomedicas, Santiago, Chile; Programa de Patologia, Universidad de Chile, Facultad de Medicina, Instituto de Ciencias Biomedicas, Santiago, Chile
3 Programa de Fisiologia y Biofisica, Universidad de Chile, Facultad de Medicina, Instituto de Ciencias Biomedicas, Santiago, Chile; Servicio de Neurologia, Hospital Sotero del Rio, Santiago, Chile
4 Departamento de Biologia, Universidad de Chile, Facultad de Ciencias, Santiago, Chile
* To whom correspondence should be addressed. E-mail: rbull{at}machi.med.uchile.cl.
We have reported that RyR-channels display three different responses to cytoplasmic free [Ca2+] depending on their redox state (Marengo et al, Biophys J 74: 1263, 1998), low, moderate and high Po. Activation by ATP of single RyR-channels from rat brain cortex was tested in planar lipid bilayers using 10 µM or 0.1 µM cytoplasmic [Ca2+]. At 10 µM [Ca2+], low Po channels presented lower apparent affinity to activation by ATP (KaATP = 422 µM) than moderate Po channels (KaATP = 82 µM). Oxidation of low Po channels with thimerosal or 2,2'-dithiodipyridine 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 the 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, which involves four independent sub-channels. Upon oxidation the sub-channels opened and closed in a concerted mode.
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