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 t he volume-sensitive amino acid release, the hyposmolarity-evoked relea se of D-[H-3]aspartate and [H-3]taurine was examined in three cell lin es: 1) wild-type Chinese hamster ovary (CHO-K1) cells, expressing an a nion exchanger activity (Cl-/SO42-) functionally similar to the erythr oid band 3; 2) a mutant CHO cell type (CHO 605) lacking this anion exc hanger activity; and 3) 293 cells in which the Cl-/HCO3- anion exchang er is absent. All cell types accumulated D-[H-3]aspartate and [H-3]tau rine under isosmotic conditions, and, similarly, in the three cell lin es, cell swelling evoked by hyposmolarity induced a rapid and transien t increase in the amino acid efflux. Blockers of the anion exchanger a nd/or Cl- channels [niflumic acid, dipyridamole, diphenylamine-2-carbo xylate, 5-nitro-2-(3-phenylpropylamino)-benzoic acid, and 4,4' -diisot hiocyanostilbene-2,2'-disulfonic acid] were potent inhibitors of amino acid efflux in the three cell lines. I-125(-) efflux, used as a marke r for Cl- fluxes, was also markedly increased in response to cell swel ling in all cell lines, and this efflux was inhibited by the anion exc hanger/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 s imilar mechanism, presumably an anion channel-like structure.