An acetazolamide-sensitive inward chloride pump in vascular smooth muscle.

In smooth muscle cells, which have a small but significant chloride ion permeability, Cl:HCO3 exchange and (Na+K+Cl) cotransport are known to act as inwardly directed chloride pumps. However, even allowing for overestimation of [Cl]i due to intracellular interference with the Cl-recording electrodes, there remained a residual accumulation of chloride in rat arterial smooth muscle under conditions in which neither of these processes is operative. Manipulation of [Cl]i and Cl permeability using pharmacological agents whilst monitoring both Em and [Cl]i showed that an acetazolamide-sensitive mechanism, perhaps a Cl-dependent ATPase, is the third pathway for Cl accumulation.