Membrane potential and intracellular chloride levels have been measured simultaneously in vascular smooth muscle from the femoral artery of the rat, in vitro, using double-barrelled chloride-sensitive microelectrodes. These values are compared in the presence and absence of bicarbonate, and inhibitors of Cl(-)-HCO3- exchange and Na(+)-K(+)-Cl- co-transport. Both DIDS and bumetanide caused a hyperpolarization of membrane potential (Em) and a fall in [Cl-]i, in the presence of extracellular HCO3-. The effects of bumetanide were reversible, but those of DIDS were not. The effect of both agents were additive. The results demonstrate that both Cl(-)-HCO3- exchange and Na(+)-K(+)-Cl- co-transport accumulate intracellular chloride in this preparation, and it is suggested that this may allow the modulation of membrane potential (and hence excitability) of smooth muscle.

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