Mechanisms of chloride transport in thymic lymphocytes

This study examined mechanisms of Cl^- transport in rat lymphocytes under a variety of conditions. Basal intracellular Cl^- concentration ([Cl^-]_i) was not different between cells assayed in the presence of HCO^-₃ or its absence (HEPES). Removal of external Cl^- resulted in a fall in [Cl^-]_i and a rapid rise in intracellular pH (pH_i). Both Cl^- efflux and the rise in pH_i were blocked by DIDS or removal of external Na⁺ but were unaffected by furosemide. The mechanisms governing Cl^- influx were assessed in cells that had been Cl^- depleted for 1 h. Reexposure to Cl^- resulted in a rapid rise in [Cl^-]_i that was partially inhibited by pretreatment with DIDS (57%) and partially inhibited by pretreatment with furosemide (45%). Pretreatment with both compounds together completely blocked Cl^- influx. Cl^- depletion caused a marked increase in pH_i that rapidly declined toward normal when the cells were reexposed to Cl^-. Preincubation with DIDS completely blocked this decrease in pH_i. In contrast, neither removal of Na⁺ nor preincubation with furosemide affected the decline in pH_i when the cells were reexposed to Cl^-. We conclude that, in thymic lymphocytes, Cl^-HCO^-₃ (or Cl^-/base exchange) regulates both Cl^- influx and efflux. Cl^- efflux is totally inhibited by DIDS and is mediated by a Na⁺-dependent Cl^-/HCO^-₃ exchanger. Cl^- influx is partially DIDS sensitive and partially furosemide sensitive and is mediated by both a Na⁺-independent Cl^-/HCO^-₃ exchanger and by a Na⁺-K⁺-2Cl^- cotransporter.