Receptor regulation of the volume-sensitive efflux of taurine and iodide from human SH-SY5Y neuroblastoma cells: differential requirements for Ca2+ and protein kinase

The basal (swelling-induced) and receptor-stimulated effluxes of 125I and taurine have been monitored to determine whether these two osmolytes are released from human SH-SY5Y cells under hypotonic conditions via common or distinct mecha-nisms. Under basal conditions, both 125I (used as a tracer for Cl) and taurine were released from the cells in a volume-dependent manner. The addition of thrombin, mediated via the proteinase-activated receptor-1 (PAR-1) subtype, significantly enhanced the release of both 125I and taurine (3–6-fold) and also increased the threshold osmolarity for efflux of these os-molytes (“set-point”) from 200 to 290 mOsM. Inclusion of a variety of broad-spectrum anion channel blockers and of 4-[(2-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid attenuated the release of both 125I an