title: Involvement of endogenous nitric oxide in the regulation of K+ channel activity in cultured human proximal tubule cells.
abstract: Nitric oxide (NO) modulates the activity of an inwardly rectifying K(+) channel in cultured human proximal tubule cells. In this study, we investigated which NO synthase (NOS) isoform(s) was involved in the endogenous production of NO and hence the regulation of channel activity. The patch-clamp experiments using the cell-attached mode showed that a nonselective NOS inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME; 100 microM), suppressed channel activity, whereas a NOS substrate, L-arginine (500 microM), stimulated it. A neuronal NOS (nNOS)/inducible NOS (iNOS)-selective inhibitor, 1-(alpha,alpha,alpha-trifluoro-o-tolyl)-imidazole (TRIM; 100 microM), suppressed channel activity to the same extent as L-NAME. TRIM also blocked the stimulatory effect of L-arginine. In contrast, an NO donor, sodium nitroprusside (10 microM) or 8-bromoguanosine 3',5'-cyclic monophosphate (100 microM) stimulated channel activity even in the presence of TRIM. RT-PCR revealed that iNOS mRNA alone was expressed in most of the cultures, i.e., 34 out of 40. In the other 6 cases, endothelial NOS (eNOS) and iNOS mRNA were simultaneously expressed. This finding was confirmed at the protein level by Western blotting. Indeed, in the patch-clamp experiments TRIM sometimes failed to suppress the channel activity, but the following addition of L-NAME suppressed it. However, since the suppressive effect of TRIM was usually similar to that of L-NAME, the involvement of eNOS in K(+) channel regulation would be relatively low. These results suggest that iNOS plays a pivotal role in the endogenous production of NO under the basal condition, which is involved in the activity of the inwardly rectifying K(+) channel in cultured human proximal tubule cells.
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: Wataru
authors.initials: W
authors.lastname: Habano
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kojo
authors.forename: You
authors.initials: Y
authors.lastname: Komagiri
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kubota
authors.forename: Manabu
authors.initials: M
authors.lastname: Kubokawa
mesh_terms: D000328:Adult; D001483:Base Sequence; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000502:physiology*; D008297:Male; D008969:Molecular Sequence Data; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D007527:Isoenzymes; D024661:Potassium Channels, Inwardly Rectifying; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D019331:NG-Nitroarginine Methyl Ester