Reaction of nitric oxide with superoxide inhibits basolateral K+ channels in the rat CCD.
We previously demonstrated that nitric oxide (NO) stimulates the basolateral small-conductance K+ channel (SK) via a cGMP-dependent pathway [M. Lu and W. H. Wang. Am. J. Physiol. 270 (Cell Physiol. 39): C1336-C1342, 1996]. Because NO at high concentration has been shown to react with superoxide (O-2) to form peroxynitrite (OONO-) [W. A. Pryor and G. L. Squadrito. Am. J. Physiol. 268 (Lung Cell. Mol. Physiol. 12): L699-L722, 1995 and M. S. Wolin. Microcirculation 3: 1-17, 1996], we extended our study to examine, using patch-clamp technique, the effect of high concentrations of NO on SK in cortical collecting duct (CCD) of rat kidney. Addition of NO donors [100-200 microM S-nitroso-N-acetyl-penicillamine (SNAP) or sodium nitroprusside (SNP)] reduced channel activity, defined as the product of channel number and open probability, to 15 and 25% of the control value, respectively. The inhibitory effect of NO was completely abolished in the presence of 10 mM Tiron, an intracellular scavenger of O-2. NO donors, 10 microM SNAP or SNP, which stimulate channel activity under control conditions, can also inhibit SK in the presence of an O-2 donor, pyrogallol, or in the presence of an inhibitor of superoxide dismutase, diethyldithiocarbamic acid. The inhibitory effect of NO is still observed in the presence of exogenous cGMP, suggesting that the NO-induced inhibition is not the result of decreased cGMP production. We conclude that the inhibitory effect of NO on channel activity results from an interaction between NO and O-2.
Department of Pharmacology, New York Medical College, Valhalla, New York 10595, USA.
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D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004050:Ditiocarb / Q000494:pharmacology; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009566:Nitrates / Q000737:chemistry / Q000494:pharmacology*; D009569:Nitric Oxide / Q000737:chemistry / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010396:Penicillamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D024681:Potassium Channels, Calcium-Activated; D011748:Pyrogallol / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026423:S-Nitroso-N-Acetylpenicillamine; D051640:Small-Conductance Calcium-Activated Potassium Channels; D013481:Superoxides / Q000737:chemistry / Q000494:pharmacology*
D009566:Nitrates; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; D051640:Small-Conductance Calcium-Activated Potassium Channels; D011748:Pyrogallol; D013481:Superoxides; D009599:Nitroprusside; C039642:peroxynitric acid; C016276:8-bromocyclic GMP; D009569:Nitric Oxide; D026423:S-Nitroso-N-Acetylpenicillamine; D004050:Ditiocarb; D010396:Penicillamine; D006152:Cyclic GMP