Abstract
Endoplasmic reticulum RyR channels from rat brain cortex were studied at the single channel level in planar lipid bilayers. The channels were activated by caffeine and locked by ryanodine at the characteristic subconductance state. RyR channels displayed either poor activation by Ca (low Po channels), moderate, bell-shaped Ca 2+ activation (moderate Po channels) or high, sigmoid Ca activation (high Po channels). Oxidation of RyR channels with thimerosal or 2,2'-dithiodipyridine changed the calcium dependence sequentially, from low to moderate to high Po, and the action of reducing agents restored the original behavior. At 10 jiM cytoplasmic [Ca], ATP activated RyR low, moderate, and high Po channels, but with different affinity; low Po channels required higher [ATP] for activation than moderate Po channels, and these required higher [ATP] than high Po. Addition of cADPR (in the presence of 100 nM calmodulin) increased 2-fold the activity of channels with moderate Ca activation, when measured at 10 \xM cytoplasmic [Ca], In contrast, cADPR had no effect on the activity of low Po channels. These combined results suggest that the redox state of RyR channels from brain modulates their response to calcium, ATP, and cADPR, which may have important physiological implications. The release of calcium through ryanodine receptor (RyR) channels of endo/sarcoplasmic reticulum is a highly regulated process that underlies many cellular responses (Berridge, 2000; Futatsugi et al9 1999; Carafoli, 2002). Several agonists/modulators, such as caffeine, Ca, and ATP, are known to activate RyR channels of cardiac and skeletal muscle (Meissner, 1994; Zucchi and Ronca-Testoni, 1997). On the
Published Version
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