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 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 approximately 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 14C-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 14C-glycine, hypoosmotic stress significantly increased glycine efflux, which was also sensitive to NPPB. In contrast, efflux of 3H-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 hypoosmotically activated anion channel was observed to be SCN- > I- > Br- > Cl- >> 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.