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

Sodium-dependent Cl(-)/HCO3 (-) 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 H2DIDS. 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 H2DIDS. The study results allow concluding that Na(+) is not required for Cl(-) efflux via Cl(-)/HCO3 (-) exchanger. NMDG in buffers cannot be used for substituting Na(+) because NMDG inhibits the exchanger.