Sodium Is Not Required for Chloride Efflux via Chloride/Bicarbonate Exchanger from Rat Thymic Lymphocytes

Sodium-dependent Cl(−)/HCO(3) (−) exchanger acts as a chloride (Cl(−)) efflux in lymphocytes. Its functional characterization had been described when Cl(−) efflux was measured upon substituting extracellular sodium (Na(+)) by N-methyl-D-glucamine (NMDG). For Na(+) and Cl(−) substitution, we have used D-mannitol or NMDG. Thymocytes of male Wistar rats aged 7–9 weeks were used and intracellular Cl(−) was measured by spectrofluorimetry using MQAE dye in bicarbonate buffers. Chloride efflux was measured in a Cl(−)-free buffer (Cl(−) substituted with isethionate acid) and in Na(+) and Cl(−)-free buffer with D-mannitol or with NMDG. The data have shown that Cl(−) efflux is mediated in the absence of Na(+) in a solution containing D-mannitol and is inhibited by H(2)DIDS. Mathematical modelling has shown that Cl(−) efflux mathematical model parameters (relative membrane permeability, relative rate of exchanger transition, and exchanger efficacy) were the same in control and in the medium in which Na(+) had been substituted by D-mannitol. The net Cl(−) efflux was completely blocked in the NMDG buffer. The same blockage of Cl(−) efflux was caused by H(2)DIDS. The study results allow concluding that Na(+) is not required for Cl(−) efflux via Cl(−)/HCO(3) (−) exchanger. NMDG in buffers cannot be used for substituting Na(+) because NMDG inhibits the exchanger.