title: Potentiation of EDHF-mediated relaxation by chloride channel blockers.
abstract: OBJECTIVE
  To investigate the involvement of Cl⁻ channels in endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation in rat mesenteric arteries.
  
  
  METHODS
  Cl⁻ channel and K(ir) channel activities were studied using whole-cell patch clamping in rat mesenteric arterial smooth muscle cells. Isometric tension of arterial rings was measured in organ chambers.
  
  
  RESULTS
  The volume-activated Cl⁻ current in rat mesenteric arterial smooth muscle cells was abolished by Cl⁻ channel blockers NPPB or DIDS. The EDHF-mediated vasorelaxation was potentiated by NPPB and DIDS. The EDHF response was diminished by a combination of apamin and charybdotoxin, which agreed with the hypothesis that EDHF response involves the release of K(+) via the Ca²(+)-activated K(+) channels in endothelial cells. The elevation of K(+) concentration in bathing solution from 1.2 mmol/L to 11.2 mmol/L induced an arterial relaxation, which was abolished by the combination of BaCl₂ and ouabain. It is consistent to the hypothesis that K(+) activates K(+)/Na(+)-ATPase and inward rectifier K(+) (K(ir)) channels, leading to the hyperpolarization and relaxation of vascular smooth muscle. The K(+)-induced relaxation was augmented by NPPB, DIDS, or withdrawal of Cl⁻ from the bathing solution, which could be reversed by BaCl₂, but not ouabain. The potentiating effect of Cl⁻ channel blockers on K(+)-induced relaxation was probably due to the interaction between Cl⁻ channels and K(ir) channels. Moreover, the K(+)-induced relaxation was potentiated when the arteries were incubated in hyperosmotic solution, which is known to inhibit volume-activated Cl⁻ channels.
  
  
  CONCLUSIONS
  The inhibition of Cl⁻ channels, particularly the volume-activated Cl⁻ channels, may potentiate the EDHF-induced vasorelaxation through the K(ir) channels.
authors.affiliation: Department of Pharmacology and Pharmacy, The University of Hong Kong, China.
authors.forename: Cui
authors.initials: C
authors.lastname: Yang
authors.forename: Yiu-wa
authors.initials: YW
authors.lastname: Kwan
authors.forename: Shun-wan
authors.initials: SW
authors.lastname: Chan
authors.forename: Simon Ming-yuen
authors.initials: SM
authors.lastname: Lee
authors.forename: George Pak-heng
authors.initials: GP
authors.lastname: Leung
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D045462:Endothelium-Dependent Relaxing Factors / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009579:Nitrobenzoates / Q000494:pharmacology*; D009994:Osmolar Concentration; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects*
chemical_list: D018118:Chloride Channels; D045462:Endothelium-Dependent Relaxing Factors; D009579:Nitrobenzoates; D024661:Potassium Channels, Inwardly Rectifying; D018999:Charybdotoxin; D001030:Apamin; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid