Volume-associated osmolyte fluxes in cell lines with or without the anion exchanger

To investigate the involvement of a red cell-type anion exchanger in the volume-sensitive amino acid release, the hyposmolarity-evoked release of D-[3H]aspartate and [3H]taurine was examined in three cell lines: 1) wild-type Chinese hamster ovary (CHO-K1) cells, expressing an anion exchanger activity (Cl-/SO4(2-)) functionally similar to the erythroid band 3; 2) a mutant CHO cell type (CHO 605) lacking this anion exchanger activity; and 3) 293 cells in which the Cl-/HCO3(-) anion exchanger is absent. All cell types accumulated D-[3H]aspartate and [3H]taurine under isosmotic conditions, and, similarly, in the three cell lines, cell swelling evoked by hyposmolarity induced a rapid and transient increase in the amino acid efflux. Blockers of the anion exchanger and/or Cl- channels [niflumic acid, dipyridamole, diphenylamine-2-carboxylate,5-nitro-2-(3-phenylpropylamino)-benzoi c acid, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid] were potent inhibitors of amino acid efflux in the three cell lines. 125I- efflux, used as a marker for Cl- fluxes, was also markedly increased in response to cell swelling in all cell lines, and this efflux was inhibited by the anion exchanger/Cl- channel blockers. These results do not support a role for an anion exchanger in the hyposmolarity-induced amino acid efflux and suggest that amino acids and Cl- may be transported by the same or a similar mechanism, presumably an anion channel-like structure.