VOLUME REGULATION IN NIH 3T3 CELLS NOT EXPRESSING P-GLYCOPROTEIN .2. CHLORIDE AND AMINO-ACID FLUXES/

The osmolyte function of amino acids and Cl in native NIH/3T3 cells no t expressing the P-glycoprotein was examined by investigating the free amino acid concentration and the swelling-activated efflux of [H-3]ta urine, as representative of amino acids, and of I-125, as a tracer for Cl. Taurine and I-125 efflux was activated by 20 and 30% hyposmotic s olutions. At 50% hyposmotic solutions, the osmolyte pool was essential ly depleted. The Cl channel blockers 5-nitro-2-(3-phenylpropylamino)be nzoic acid, 1,9-dideoxyforskolin, dipyridamole, and niflumic acid inhi bited the release of the two osmolytes by 80-95%. 4,4'-Diisothiocyanos tilbene-2,2'-disulfonic acid (400 mu M) decreased the efflux of taurin e 80% without affecting that of I-125. Linolenic and arachidonic acids (5-20 mu M) showed a concentration-dependent inhibitory effect on tau rine and I-125 fluxes. Omission of Ca decreased osmolyte fluxes by 16% . Verapamil inhibited the osmolyte release only at 500 mu M. Nimodipin e at 25 and 50 mu M decreased the release of [H-3]taurine and I-125 by similar to 60 and 80%, respectively, but this effect was independent of the presence of extracellular Ca. These results indicate that amino acids and Cl function as osmolytes during regulatory volume decrease in native NIH/3T3 cells.