SIMILAR PROPERTIES OF TAURINE RELEASE INDUCED BY POTASSIUM AND HYPOSMOLARITY IN THE RAT RETINA

Increasing external K+ concentration to 56, 75 or 100 mm stimulated taurine release by 3-, 7- and 11-fold, respectively. The K+-evoked release of [3H]taurine was markedly delayed, sustained and Ca2+-independent, in clear contrast to the usual neurotransmitter release pattern. These high K+ concentrations caused a marked increase in retinal cell volume which was prevented by removal of Cl-, or in hyperosmotic solutions. In these conditions [3H]taurine release also was abolished, suggesting an association of taurine efflux and cell swelling. Taurine release was also markedly increased 10- and 20-fold upon reduction of external osmolarity by 25 and 50%, respectively. Both, K+- and hyposmolarity-induced release were markedly inhibited by DIDS and quinidine. Total inhibition of the K+-evoked release was observed at 200 μm DIDS or 1 mm quinidine, whereas the drugs inhibited the hyposmolarity-evoked release by 50 and 68% respectively, at these concentrations. It is suggested that swelling is the signal for the K+-induced taurine release from rat retina. © 1991.