title: Role of chloride transport proteins in the vasorelaxant action of nitroprusside in isolated rat aorta.
abstract: Chloride ions play a key role in smooth muscle contraction, but little is known concerning their role in smooth muscle relaxation. Here we investigated the effect of chloride transport inhibitors on the vasorelaxant responses to nitroprusside in isolated and endothelium-denuded rat aorta, precontracted with phenylephrine 1 muM. Incubation of aortic rings in NO(3)(-) media strongly potentiated the vasorelaxant responses to nitroprusside. Bumetanide, DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) and acetazolamide strongly potentiated the vasorelaxant responses to nitroprusside (by 70-100%). EC(50) were 2.3+/-0.5 microM for bumetanide, 26+/-15 microM for DIDS and 510+/-118 microM for acetazolamide (n=6 for condition). Niflumic acid, a selective inhibitor of ClCa (calcium-activated chloride channels), potentiated nitroprusside relaxation to a similar extent as chloride transport inhibitors, in a non-additive manner. Zinc and nickel ions, both modestly potentiated nitroprusside vasorelaxation (by 20-30%). Cobaltum had negligible effect on nitroprusside vasorelaxation. CPA (p-chlorophenoxy-acetic acid), an inhibitor of volume-sensitive chloride channels (ClC), slightly potentiated nitroprusside vasorelaxation (by 15%), and the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel inhibitors CFTR(inh)172 (5-[(4-Carboxyphenyl)methylene]-2-thioxo-3-[(3-trifluoromethyl)phenyl-4-thiazolidinone), DPC (diphenylamine-2,2'-dicarboxylic acid) and glibenclamide were without significant effect. In conclusion, inhibition of chloride transport proteins strongly potentiates the vasorelaxant responses to nitroprusside in isolated rat aorta. This effect seems mediated by chloride depletion and inhibition of a chloride channel activated by both, calcium and cyclic GMP (cGMP).
authors.affiliation: Department of Physiology and Pharmacology, School of Medicine, University of Zaragoza, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Valero
authors.forename: Désirée
authors.initials: D
authors.lastname: Pereboom
authors.forename: Ricardo P
authors.initials: RP
authors.lastname: Garay
authors.forename: José Octavio
authors.initials: JO
authors.lastname: Alda
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects*; D002118:Calcium / Q000502:physiology; D002412:Cations / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism / Q000502:physiology; D003470:Culture Media; D006152:Cyclic GMP / Q000502:physiology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009566:Nitrates / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters / Q000502:physiology*; D064506:Solute Carrier Family 12, Member 2; D014665:Vasodilator Agents / Q000494:pharmacology*
chemical_list: D002412:Cations; D018118:Chloride Channels; D002712:Chlorides; D003470:Culture Media; D009566:Nitrates; C578879:Slc12a2 protein, rat; D049994:Sodium Potassium Chloride Symporter Inhibitors; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D014665:Vasodilator Agents; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D009599:Nitroprusside; D006152:Cyclic GMP; D002118:Calcium