Evidence against a contribution by Na(+)‐Cl‐ cotransport to chloride accumulation in rat arterial smooth muscle.

Abstract

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.

The three mechanisms of intracellular chloride accumulation in vascular smooth muscle of human umbilical and placental arteries

“…The third system is an entity designated "pump III". This functions independently of Na + and HCO 3 -and it is unaffected by inhibitors of Cl -/HCO 3 -exchange and (Na+K+Cl) cotransport but it has only been found in one smooth muscle so far, namely, rat femoral arterial smooth muscle [6,9]. Once again, its activity can affect contractility and, like (Na+K+Cl) cotransport, it is stimulated by noradrenaline [5,10].…”

Increased (Na+K+Cl) Cotransport in Rat Arterial Smooth Muscle in Deoxycorticosterone (DOCA)/Salt-Induced Hypertension

“…To apply equation (3), [Cl] i has to be lowered towards equilibrium, which can be achieved by blocking cotransport with bumetanide [3, 13, 14, 15]and then [K] o has to be changed so as to alter E m . As usual, there was a small hyperpolarisation on applying bumetanide and, as [K] o was increased step-wise to 20 m M , E m depolarised.…”

“…The other two processes which drive Cl inward are (Na+K+Cl) cotransport and a novel entity which we have called ‘pump III’ [13, 14]which is also enhanced in DOCA-salt hypertension [15]. Thus, the increase in [Cl] i in hypertension seemed to occur because the activity of cotransport and ‘pump III’ both roughly doubled [15].…”

“…This equation cannot be solved directly but if [Cl] i is brought close to equilibrium by blocking inward Cl pumping by cotransport with bumetanide [3, 13, 14, 15], then the terms in [Cl] are not relevant. Equation (2) can then be rearranged into the linear form:…”

Peroxynitrite hyperpolarizes smooth muscle and relaxes internal carotid artery in rabbit via ATP-sensitive K+ channels

“…It seems unlikely, however, that Cl Ϫ channels contribute to hyperpolarization induced by X/XOϩSNP, because of the following observations. 1) The equilibrium potential of Cl Ϫ in vascular tissue is between Ϫ11 and Ϫ50 mV (3,11,24). Resting membrane potential of rabbit internal carotid artery in this study was Ϫ48.8 mV, so opening of Cl Ϫ channels would be expected to depolarize, not hyperpolarize, the vascular membrane.…”