Separate taurine and chloride efflux pathways activated during regulatory volume decrease

Separate taurine and chloride efflux pathways activated during regulatory volume decrease. Am. J. Physiol. 277 (Cell Physiol. 46): C392-C402, 1999.-Organic osmolyte and halide permeability pathways activated in epithelial HeLa cells by cell swelling were studied by radiotracer efflux techniques and single-cell volume measurements. The replacement of extracellular Cl- by anions that are more permeant through the volume-activated Cl- channel, as indicated by electrophysiological measurements, significantly decreased taurine efflux. In the presence of less-permeant anions, an increase in taurine efflux was observed. Simultaneous measurement of the I-125, used as a tracer for Cl-, and [H-3]taurine efflux showed that the time courses for the two effluxes differed. In Cl-rich medium the increase in I- efflux was transient, whereas that for taurine was sustained. Osmosensitive Cl- conductance, assessed by measuring changes in cell volume, increased rapidly after hypotonic shock. The influx of taurine was able to counteract Cl- conductance-dependent cell shrinkage but only similar to 4 min after triggering cell swelling. This taurine-induced effect was blocked by DIDS. Differences in anion sensitivity, the time course of activation, and sensitivity to DIDS suggest that the main cell swelling-activated permeability pathways for taurine and Cl- are separate.