The uptake of 36Cl- into cells was measured after preincubation in medium containing nigericin and KCl to allow control of the intracellular pH. When the pH was increased from pH 7.0 to pH 7.3 there was a 10-fold increase in the rate of 36Cl- uptake. The increase was half maximal at pH 7.15 in Vero and L-cells, whereas in phorbol 12-myristate 13-acetate-treated Vero cells the increase was half maximal at pH 6.9. Kinetic studies showed that in cells preincubated with nigericin and isotonic KCl, both at pH 7.0 and at pH 8.0, the Km for Cl- was 7 mM. In the two cases the Jmax was 1.7 X 10(8) Cl- ions X cell-1 X s-1 and 1.6 X 10(9) Cl- ions X cell-1 X s-1, respectively. Bicarbonate inhibited 36Cl- uptake with a Ki of 5-6 mM. Probably, the anion antiporter plays a role in the regulation of the intracellular pH.

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