title: Regulation of an inwardly rectifying K+ channel by nitric oxide in cultured human proximal tubule cells.
abstract: We investigated the effects of nitric oxide (NO) on activity of the inwardly rectifying K(+) channel in cultured human proximal tubule cells, using the cell-attached mode of the patch-clamp technique. An inhibitor of NO synthases, N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 microM), reduced channel activity, which was restored by an NO donor, sodium nitroprusside (SNP; 10 microM) or 8-bromo-cGMP (8-BrcGMP; 100 microM). However, SNP failed to activate the channel in the presence of an inhibitor of soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 microM). Similarly, the SNP effect was abolished by a protein kinase G (PKG)-specific inhibitor, KT-5823 (1 microM), but not by a protein kinase A-specific inhibitor, KT-5720 (500 nM). Another NO donor, S-nitroso-N-acetyl-D,L-penicillamine (10 microM), mimicked the SNP-induced channel activation. In contrast to the stimulatory effect of SNP at a low dose (10 microM), a higher dose of SNP (1 mM) reduced channel activity, which was not restored by 8-BrcGMP. Recordings of membrane potential with the slow whole cell configuration demonstrated that l-NAME (100 microM) and the high dose of SNP (1 mM) depolarized the cell by 10.1 +/- 2.6 and 9.2 +/- 1.0 mV, respectively, whereas the low dose of SNP (10 microM) hyperpolarized it by 7.1 +/- 0.7 mV. These results suggested that the endogenous NO would contribute to the maintenance of basal activity of this K(+) channel and hence the potential formation via a cGMP/PKG-dependent mechanism, whereas a high dose of NO impaired channel activity independent of cGMP/PKG-mediated processes.
authors.affiliation: Department of Physiology II, Iwate Medical University School of Medicine, Morioka, 020-8505 Japan.
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Nakamura
authors.forename: Junko
authors.initials: J
authors.lastname: Hirano
authors.forename: Manabu
authors.initials: M
authors.lastname: Kubokawa
mesh_terms: D000328:Adult; D002227:Carbazoles / Q000494:pharmacology; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D005260:Female; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007687:Kidney Tubules, Proximal / Q000166:cytology*; D008564:Membrane Potentials / Q000502:physiology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000502:physiology*; D011758:Pyrroles / Q000494:pharmacology
chemical_list: D002227:Carbazoles; D004791:Enzyme Inhibitors; D007211:Indoles; D020030:Nitric Oxide Donors; D024661:Potassium Channels, Inwardly Rectifying; D011758:Pyrroles; D009599:Nitroprusside; D009569:Nitric Oxide; C057416:KT 5720; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester