Taurine release and swelling of cerebral cortex slices from adult and developing mice in media of different ionic compositions.

The release of preloaded radiolabeled taurine was studied in superfused cerebral cortex slices obtained from adult and 3-day-old mice in media of varying ionic composition. Our aim was to establish whether the release of taurine from slices evokable by high concentrations of K+ could be attributed solely to cell volume changes or whether it results directly from depolarization of cell membranes. In both age groups hypoosmotic media enhanced the release of taurine. The enhancement was greater in 3-day-old than in adult mice. The K(+)-evoked release of taurine was likewise greater in slices from 3-day-old mice than in slices from adult mice. The K+ stimulation was totally preserved in adult mice and partially preserved in 3-day-old mice when the slices were superfused with Cl(-)-free media, with media in which the K+ x Cl- ionic product was kept constant and with hyperosmotic high-K+ media. The results were practically the same when the permeant anion acetate and the impermeant anion gluconate were used to replace the Cl- deficit. The unstimulated release of preloaded taurine was greatly enhanced in Cl(-)-free media in both age groups. There obtained no statistically significant correlation between the intracellular swelling of slices and the magnitude of taurine release under the present different experimental conditions in either age group. The results show that the K(+)-evoked release of taurine from superfused cerebral cortex slices cannot be solely attributed to depolarization-induced cell swelling. At least a part of the release results directly from membrane depolarization which besides exocytosis apparently also enhances the carrier-mediated release of taurine and inhibits the reuptake of taurine liberated from intracellular compartments.