Evidence against a contribution by Na(+)-Cl- cotransport to chloride accumulation in rat arterial smooth muscle.
1. Chloride accumulation into rat saphenous arterial smooth muscle has been examined using chloride-sensitive microelectrodes, to assess the contribution of Na(+)-Cl-cotransport. 2. Bumetanide (10 microM) produced a fall in intracellular chloride ([Cl-]i), and a hyperpolarization of membrane potential (Em). However, [Cl-]i remained above the equilibrium level predicted from the membrane potential, indicating a residual accumulation. 3. Replacement of extracellular sodium with N-methyl-D-glucamine or choline caused a fall in [Cl-]i similar to that observed with bumetanide, but the hyperpolarization of Em was larger. In Na(+)-free media, bumetanide had no effect. [Cl-]i remained significantly above equilibrium. 4. In the presence of bumetanide, chlorothiazide produced a further dose-dependent fall in [Cl-]i, and hyperpolarization of Em. However, although [Cl-]i fell more than with bumetanide alone, it remained significantly above equilibrium. Metolazone was without effect at 100 microM. 5. In the presence of bumetanide, ethacrynic acid and N-ethyl maleimide caused a dose-dependent hyperpolarization of Em and a fall in [Cl-]i to equilibrium. 6. The third inward chloride pump in rat saphenous arterial smooth muscle appears not to be a form of Na(+)-Cl- cotransport. The potency series of thiazide diuretic action (acetazolamide > chlorothiazide > metolazone) differed significantly from that published for Na(+)-Cl- cotransport, and there is no sodium dependence.
Davis
J P
JP
Department of Anatomy & Physiology, University of Dundee, UK.
D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D002034:Bumetanide / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism*; D004232:Diuretics / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004976:Ethacrynic Acid / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D049992:Sodium Chloride Symporters; D027981:Symporters
D002352:Carrier Proteins; D002712:Chlorides; D004232:Diuretics; D004791:Enzyme Inhibitors; D049992:Sodium Chloride Symporters; D027981:Symporters; D002034:Bumetanide; D012964:Sodium; D004976:Ethacrynic Acid; D005033:Ethylmaleimide