A redox O2 sensor modulates the SR Ca2+ countercurrent through voltage- and Ca(2+)-dependent Cl- channels.
The activity of a relatively small Cl- (SCl) channel in the sarcoplasmic reticulum (SR) vesicles of rabbit skeletal muscle was preserved following their reconstitution into lipid bilayer. Reducing PO2 from approximately 150 to < 1 Torr in the cis-side (cytosolic) reversibly inhibited the channel activity within 2 min. The modulatory effects, deduced from reduction in Cl- current levels and in kinetic parameters of channel activation, in normoxic (PO2 approximately 150 Torr) and hypoxic (low PO2 < 1 Torr) solutions were mimicked by oxidizing and reducing agents, respectively. Cl- current transitions to the main open conductance state were increased by 100 microM of the specific sulfhydryl (SH)-oxidizing agent 4,4'-dithiodipyridine and inhibited by the SH-reducing agent glutathione (GSH) with a Hill coefficient of 8 and inhibition constant of approximately 3.1 mM. The inhibitory effects of 5 mM [GSH]cis were prevented by prior addition of 1 mM iodoacetamide, an alkylating agent, to the cytosolic side of the channel. These findings suggest that an SH-dependent mechanism (redox couple, e.g., reduced/oxidized glutathione) could be involved in the gating of the SCl channel in such a way that SH oxidation (GSSH) favors the open state of the channel, and SH reduction (GSH), which mimics the inhibitory action of low PO2, favors the closed state.
Kourie
J I
JI
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra City, Australian Capital Territory, Australia.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D018118:Chloride Channels / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D004220:Disulfides / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D005978:Glutathione / Q000494:pharmacology; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010313:Partial Pressure; D011725:Pyridines / Q000494:pharmacology; D011817:Rabbits; D019163:Reducing Agents / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism
D018118:Chloride Channels; D004220:Disulfides; D016877:Oxidants; D011725:Pyridines; D019163:Reducing Agents; D013438:Sulfhydryl Compounds; C007542:4,4'-dipyridyl disulfide; D005978:Glutathione; D010100:Oxygen; D002118:Calcium; D004229:Dithiothreitol