Carbon monoxide stimulates the apical 70-pS K+ channel of the rat thick ascending limb.
We have investigated the expression of heme oxygenase (HO) in the rat kidney and the effects of HO-dependent heme metabolites on the apical 70-pS K+ channel in the thick ascending limb (TAL). Reverse transcriptase-PCR (RT-PCR) and Western blot analyses indicate expression of the constitutive HO form, HO-2, in the rat cortex and outer medulla. Patch-clamping showed that application of 10 microM chromium mesoporphyrin (CrMP), an inhibitor of HO, reversibly reduced the activity of the apical 70-pS K+ channel, defined by NPo, to 26% of the control value. In contrast, addition of 10 microM magnesium protoporphyrin had no significant effect on channel activity. HO involvement in regulation of the apical 70-pS K+ channel of the TAL, was further indicated by the addition of 10 microM heme-L-lysinate, which significantly stimulated the channel activity in cell-attached patches by 98%. The stimulatory effect of heme on channel activity was also observed in inside-out patches in the presence of 0.5-1 mM reduced nicotinamide adenine dinucleotide phosphate. This was completely abolished by 10 microM CrMP, suggesting that a HO-dependent metabolite of heme mediated the effect. This was further supported by exposure of the cytosolic membrane of inside-out patches to a carbon monoxide-bubbled bath solution, which increased channel activity. Moreover, carbon monoxide completely abolished the effect of 10 microM CrMP on the channel activity. In contrast, 10 microM biliverdin, another HO-dependent metabolite of heme, had no effect. We conclude that carbon monoxide produced from heme via an HO-dependent metabolic pathway stimulates the apical 70-pS K+ channel in the rat TAL.
Liu
H
H
Department of Pharmacology, New York Medical College, Valhalla, New York 10595, USA.
Mount
D B
DB
Nasjletti
A
A
Wang
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W
D000818:Animals; D001664:Biliverdine / Q000494:pharmacology; D002248:Carbon Monoxide / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006418:Heme / Q000031:analogs & derivatives / Q000494:pharmacology; D006419:Heme Oxygenase (Decyclizing) / Q000096:biosynthesis* / Q000235:genetics; D007668:Kidney / Q000201:enzymology*; D008239:Lysine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D009249:NADP / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011166:Porphyrins / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
D004791:Enzyme Inhibitors; D011166:Porphyrins; D015221:Potassium Channels; C106087:heme lysinate; D006418:Heme; D009249:NADP; D012313:RNA; D002248:Carbon Monoxide; D006419:Heme Oxygenase (Decyclizing); C105245:heme oxygenase-2; D008239:Lysine; D001664:Biliverdine