[H-3]taurine and D-[H-3]aspartate release from astrocyte cultures are differently regulated by tyrosine kinases

Volume-dependent anion channels permeable for Cl- and amino acids are thoug ht to play an important role in the homeostasis of cell volume. Astrocytes are the main cell type in the mammalian brain showing volume perturbations under physiological and pathophysiological conditions. We investigated the involvement of tyrosine phosphorylation in hyposmotic medium-induced [H-3]t aurine and D-[H-3]aspartate release from primary astrocyte cultures. The ty rosine kinase inhibitors tyrphostin 23 and tyrphostin A51 partially suppres sed the volume-dependent release of [H-3]taurine in a dose-dependent manner with half-maximal effects at similar to 40 and 1 mu M, respectively. In co ntrast, the release of D-[H-3]aspartate was not significantly affected by t hese agents in the same concentration range. The inactive analog tyrphostin 1 had no significant effect on the release of both amino acids. The data o btained suggest the existence of at least two volume-dependent anion channe ls permeable to amino acids in astrocyte cultures. One of these channels is permeable to taurine and is under the control of tyrosine kinase(s). The o ther is permeable to both taurine and aspartate, but its volume-dependent r egulation does not require tyrosine phosphorylation.