Mechanisms of chloride transport in crayfish stretch receptor neurones and guinea pig vas deferens: implications for inhibition mediated by GABA.

Since activation of GABAA receptors is believed to open an associated Cl- channel, the intracellular Cl- activity (aiCl) must be lower than that predicted from a passive distribution, to account for hyperpolarizing responses, or higher, to account for depolarizing responses. The physiological and pharmacological properties of the implied Cl- extruding and accumulating mechanisms have been investigated by direct measurements of aiCl. A coupled K+-Cl- co-transport has been found in crayfish stretch receptor neurones and a predominating Cl(-)HCO3(-) exchange in guinea pig vas deferens. From the different ionic mechanisms involved in Cl- extrusion and accumulation, it is proposed that drugs which affect Cl- transport mechanisms will reduce GABA responses of both polarities only if their action is via interference with the Cl- recognition site, but not if it is via interference with the co- or counter-ion recognition site.