title: Blockade of chloride channels reveals relaxations of rat small mesenteric arteries to raised potassium.
abstract: 1. Raised extracellular K(+) relaxes some arteries, and has been proposed as Endothelium-Derived Hyperpolarizing Factor (EDHF). However, relaxation of rat small mesenteric arteries to K(+) is highly variable. We have investigated the mechanism of K(+)-induced dilatation and relaxation of pressurized arteries and arteries mounted for measurement of isometric force. 2. Raising [K(+)](o) from 5.88 - 10.58 mM did not dilate or relax pressurized or isometric arteries. Relaxation to raised [K(+)](o) was revealed in the presence of 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB); this effect of NPPB was concentration-dependent (IC(50): 1.16 microM). 3. Relaxations to raised [K(+)](o) in the presence of NPPB, were abolished by 30 microM Ba(2+) or endothelial-denudation. Acetycholine (10 microM) relaxed endothelium-intact arteries in presence of raised [K(+)](o) NPPB and Ba(2+). 4. Relaxations to raised [K(+)](o) were revealed in hyperosmotic superfusate (+60 mM sucrose). These relaxations were abolished by 30 microM Ba(2+). In the presence of raised [K(+)](o), 60 mM sucrose and 30 microM Ba(2+), 10 microM acetycholine still relaxed all arteries. 5. Fifty microM 18 alpha-glycyrrhetinic acid (18 alpha-GA), a gap junction inhibitor, depressed relaxations to both 10 microM acetylcholine and raised [K(+)](o), in the presence of 10 microM NPPB. 6. In summary, blockade of a volume-sensitive Cl(-) conductance in small rat mesenteric arteries, using NPPB or hyperosmotic superfusion, reveals a endothelium-dependent, Ba(2+) sensitive dilatation or relaxation of rat mesenteric arteries to raised [K(+)](o). We conclude that inwardly rectifying potassium channels on the endothelium underlie relaxations to raised [K(+)](o) in rat small mesenteric arteries.
authors.affiliation: Department of Physiology, University of Bristol, University Walk, Bristol, BS8 1TD.
authors.forename: J M
authors.initials: JM
authors.lastname: Doughty
authors.forename: J P
authors.initials: JP
authors.lastname: Boyle
authors.forename: P D
authors.initials: PD
authors.lastname: Langton
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology; D017629:Gap Junctions / Q000187:drug effects; D006034:Glycyrrhetinic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008638:Mesenteric Arteries / Q000187:drug effects* / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D009578:Nitrobenzenes / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D018118:Chloride Channels; D009578:Nitrobenzenes; C119129:18alpha-glycyrrhetinic acid; D001464:Barium; C047633:5-(4-nitrophenyl)-2,4-pentadienal; D000109:Acetylcholine; D006034:Glycyrrhetinic Acid; D011188:Potassium