Chloride transport in human placental microvillus membrane vesicles. I. Evidence for anion exchange.

36Cl uptake by microvillus brush border membrane vesicles prepared from normal term human placenta has been studied using an ion exchange column assay and a novel method to correct for vesicle recovery. Uptake of this anion, which was largely into an osmotically active space, was time dependent with a half-time of approximately 4 min at 4 degrees C. DIDS at a maximal inhibitory concentration inhibited 36Cl uptake by approximately 40%; furosemide (10(-4)M) showed a similar degree of inhibition and the effects of the two drugs appeared not to be additive. Anions including Cl, Br, I, NO3, salicylate and SCN reduced 36Cl uptake, the latter two being the most potent; gluconate was without effect. Inhibition by maximal inhibitory concentrations of DIDS and the anions SCN and salicylate was not additive. Neither the DIDS-sensitive nor the SCN-sensitive component of 36Cl uptake was influenced by membrane potential; in contrast the inhibitor-insensitive component was increased by an inside positive membrane potential. These findings suggest that under the conditions employed an electroneutral anion exchange system is responsible for approximately half of the chloride flux across this plasma membrane.