title: Hypoxia and alkalinization inhibit endothelium-derived nitric oxide but not endothelium-derived hyperpolarizing factor responses in porcine coronary artery.
abstract: We investigated the mechanisms by which hypoxia and alkalinization inhibit the endothelium-dependent relaxation to Substance P (SP) in porcine coronary artery. In a KCl contracture, the major component of the SP response is endothelium-derived nitric oxide (EDNO), whereas with receptor-mediated 9,11-dideoxy-llalpha, 9alpha-epoxymethanoprostaglandin F(2alpha) (U46619) stimulation, the SP response is dependent on both EDNO and endothelium-derived hyperpolarization factor. Intracellular alkalinization by NH(4)Cl reduced the peak of SP responses when arteries were contracted with KCl, whereas with U46619 stimulation, the peak was little effected but the duration was shortened. In endothelial cell-denuded arteries, alkalinization with NH(4)Cl shifted the sodium nitroprusside concentration-relaxation relations rightward. The effects of NH(4)Cl in SP- and sodium nitroprusside-induced relaxations were attenuated by decreasing extracellular pH (pH(o)) from 7.4 to 7.2, which normalized intracellular pH (pH(i)) to control levels. In contrast, in U46619 contractures, the SP response in the presence of a NO synthase inhibitor was unaffected by NH(4)Cl. Moreover, hypoxia blunted but did not abolish the responses to SP for U46619 contractures; addition of KCl, however, abolished the SP response under hypoxia. Endothelial [Ca(2+)](i) was measured with fura-2 differentially loaded only into endothelial cells on intact arteries. Despite the attenuation of the SP response in KCl contractures by NH(4)Cl or hypoxia, endothelial [Ca(2+)](i) responses were unchanged. Our results suggest that hypoxia and alkalinization inhibit EDNO but not endothelium-derived hyperpolarization factor relaxations through a mechanism(s) not involving endothelial cell [Ca(2+)](i). Inhibition of EDNO relaxation by alkalinization with NH(4)Cl is likely to occur at the level of activation of guanylate cyclase and/or at a step downstream in smooth muscle.
authors.affiliation: Department of Molecular and Cellular Physiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shimizu
authors.forename: R J
authors.initials: RJ
authors.lastname: Paul
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001685:Biological Factors / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004730:Endothelium, Vascular / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology; D013373:Substance P / Q000494:pharmacology; D013552:Swine; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D001685:Biological Factors; C067410:endothelium-dependent hyperpolarization factor; D000643:Ammonium Chloride; D009599:Nitroprusside; D016718:Arachidonic Acid; D009569:Nitric Oxide; D013373:Substance P; D003577:Cytochrome P-450 Enzyme System; D002118:Calcium