Effects of acetylcholine on potassium-induced changes of GABA and taurine uptakes and release in cerebral cortex slices from the rat.

Acetylcholine, in presence of eserine, has little or no effect on the potassium-ion-suppressed concentrative uptakes of GABA and taurine by rat brain cortex slices in contrast with its effect on those of L-glutamate, L-aspartate, and glycine. Potassium ions at a concentration of 30 muequiv./ml in the incubation medium has a marked suppressive effect on the uptakes of GABA and taurine when there is no apparent change in the sodium ion content of the brain tissue. It is concluded that some factor, besides the change in sodium gradient, operates in the mechanism of potassium suppression of GABA and taurine uptakes. Acetylcholine diminishes the potassium-evoked release of endogenous GABA and taurine from brain slices. Its action is Ca2+ dependent and is diminished by atropine. Acetylcholine does not affect the potassium-accelerated release of GABA from brain slices previously loaded with this amino acid. The differences in uptake and release phenomena exhibited by GABA and taurine from those of L-glutamine and L-aspartate may be due to differences between the mechanisms, as well as the sites, of cerebral uptake and release of these two groups of amino acids.