SWELLING-ACTIVATED AMINO-ACID EFFLUX IN THE HUMAN NEUROBLASTOMA CELL-LINE CHP-100

1. The effects of hypoosmotic stress on cell volume and amino acid eff lux were evaluated in the human neuroblastoma cell line CHP-100 with t he Coulter Counter Multisizer and radiolabeled amino acid efflux, resp ectively. 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, hypoosmot ic stress induced a 300 +/- 22% (n = 23, P < 0.05) increase in taurine efflux compared with controls. This efflux was inhibited by the chlor ide channel blockers 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPP B), 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 ext racellular calcium. 4. Similarly, in cells loaded with C-14-glycine, h ypoosmotic stress significantly increased glycine efflux, which was al so sensitive to NPPB. In contrast, efflux of H-3-glutamate was not sig nificantly altered after hypoosmotic stress.5. With the use of patch c lamp recording techniques, Cl- channels were activated in cell attache d patches after exposure to hypoosmotic solutions. 6. In nystatin perf orated patches, permeability of the hypoos motically activated anion c hannel was observed to be SCN- > I- > Br- > Cl- much greater than Glut amate. 7. It is concluded that in CHP-100 cells, anion channels are ac tivated during hypoosmotic stress and these channels represent a pathw ay for efflux of amino acids.