Stimulation of intracellular chloride accumulation by noradrenaline and hence potentiation of its depolarization of rat arterial smooth muscle in vitro

1 Double-barrelled ion-selective microelectrodes were used to examine the effects of exogenous noradrenaline upon the membrane potential (E-m) and intracellular chloride concentration ([Cl](i)) of arterial smooth muscle from the saphenous branch of the femoral artery of the rat. 2 After treatment with 0.6 mM 6-hydroxydopamine (to functionally denervate the tissue), exogenous noradrenaline (5 nM) caused repeatable depolarization of E-m from -63.7+/-2.4 mV (s.d., n=18) to -53.8+/-3.4 mV (P<0.0001) and increases in [Cl](i) from 31.0+/-0.5 mM to 42.5+/-2.2 mM (P<0.0001). 3 In the presence of 10 mu M bumetanide (an inhibitor of (Na-K-Cl) cotransport), 5 nM noradrenaline caused a depolarization of E-m of 3.0+/-3.2 mV, and a rise in [Cl](i) of 4.5+/-2.5 mM. 4 In the presence of bumetanide and 1 mM acetazolamide (used as an inhibitor of a Na-independent inward Cl pump), noradrenaline had no effect on E-m or [Cl](i). 5 In the absence of extracellular chloride, the rise in apparent [Cl](i) in response to 5 nM noradrenaline was abolished but there was a depolarization of 2.0+/-3.9 mV. 6 These results are consistent with the stimulation of (Na-K-Cl) cotransport and a Na-independent Cl pump by exogenous noradrenaline and with the consequent increase in [Cl](i) and shift in E-Cl potentiating the depolarization caused by noradrenaline. The possibility that modulation of [Cl](i) may be a general mechanism of E-m regulation is discussed.