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, Nω-nitro-l-arginine methyl ester (l-NAME; 100 μM), reduced channel activity, which was restored by an NO donor, sodium nitroprusside (SNP; 10 μM) or 8-bromo-cGMP (8-BrcGMP; 100 μM). 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 μM). Similarly, the SNP effect was abolished by a protein kinase G (PKG)-specific inhibitor, KT-5823 (1 μM), but not by a protein kinase A-specific inhibitor, KT-5720 (500 nM). Another NO donor, S-nitroso- N-acetyl-d,l-penicillamine (10 μM), mimicked the SNP-induced channel activation. In contrast to the stimulatory effect of SNP at a low dose (10 μM), 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 μM) 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 μM) 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.