The effect of gamma-aminobutyric acid on the potassium movements of rat cortical synaptosomes.

K+ fluxes of rat cortical synaptosomes were monitored by a K+ sensitive ion-selective membrane electrode. The uptake phases of K+curves from control and experimental measurements were compared and statistically evaluated. GABA significantly reduced K+ uptake but it was able to reverse the decrease of K+ uptake caused by protoveratrine. In the absence of Ca2+ the K+ uptake was diminished; GABA had no effect on this inhibition. The effect of GABA on K+ take was partially reduced by bicuculline and abolished by diamino-butyric acid. The K+ content of synaptosomes decreased, while the NA+ content increased in the presence of GABA. The results are discussed in association with presynaptic depolarisation and with modulatory effects of GABA on the release of other transmitters.