1. The effects of hypoosmotic stress on cell volume and amino acid efflux were evaluated in the human neuroblastoma cell line CHP-100 with the Coulter Counter Multisizer and radiolabeled amino acid efflux, respectively.
2. CHP-100 cells swelled by similar to 35 +/- 5% (means +/- SE) when the osmolarity of the solution was decreased from 290 to 190 mOsm/kg H2O. The rapid swelling was followed by a biphasic regulatory volume decrease (RVD).
3. In cells loaded with C-14-taurine, hypoosmotic stress induced a 300 +/- 22% (n = 23, P <0.05) increase in taurine efflux compared with controls. This efflux was inhibited by the chloride channel blockers 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), 4,4'-diisothio-cyanostilbene-2,2'-disulfonic acid (DIDS), niflumic acid and by the volume-activated anion channel blocker tamoxifen. In addition, the swelling-activated taurine efflux was dependent upon extracellular calcium.
4. Similarly, in cells loaded with C-14-glycine, hypoosmotic stress significantly increased glycine efflux, which was also sensitive to NPPB. In contrast, efflux of H-3-glutamate was not significantly altered after hypoosmotic stress.
5. With the use of patch clamp recording techniques, Cl- channels were activated in cell attached patches after exposure to hypoosmotic solutions.
6. In nystatin perforated patches, permeability of the hypoos motically activated anion channel was observed to be SCN- > I- > Br- > Cl- much greater than Glutamate.
7. It is concluded that in CHP-100 cells, anion channels are activated during hypoosmotic stress and these channels represent a pathway for efflux of amino acids.