A volume-dependent, chloride-sensitive component of taurine release stimulated by potassium from retina

Chick retinas exposed to 56 mM KCl showed marked swelling of cells and synaptic structures, detected by morphological examination as well as by measurements of cell water content. Retinal cell swelling is prevented by omission of chloride. Potassium chloride, 56 mM, elicited the efflux of [3H]taurine by a process that is partly calcium-dependent, highly chloride-dependent (80%), and sensitive to furosemide. The release of [3H]dopamine under the same conditions is completely calcium-dependent and increases in the absence of chloride. The chloride-dependent component of [3H]taurine efflux seems related to increases in volume changes since it is markedly reduced when cell swelling is prevented either by maintaining constant the K X Cl product (Donnan equilibrium) or by making the solution hypertonic with mannitol. Omission of calcium and of chloride showed additive effects, practically suppressing the potassium-stimulated release of taurine. These results suggest that the potassium-stimulated efflux of [3H]taurine consists of a large component associated to changes in cell volume and a small component probably related to the depolarizing effects of potassium.