Uptake of serotonin, gamma-aminobutyric acid and histamine into synaptic vesicles of the pig caudate nucleus.

Dopamine-containing vesicles were isolated from the caudate nucleus of the pig by differential centrifugation and incubated with 14-C-serotonin (14-C-5-HT), 14-C-gamma-aminobutyric acid (14-C-GAGA), 14-C-dopamine or 14-C-histamine. At 25 degrees C the uptake of 14-C-5-HT and 14-C-GABA was enhanced by ATP and magnesium. The Km for the uptake of 14-C-5-HT in the presence of ATP and magnesium was 0.67 x 10-6M, that of 14-C-GABA 1.33 x 10-4M. 14-C-Histamine was also taken up into the vesicles but its uptake was not incluenced by ATP and magnesim. The ATP-magnesium-dependent uptake of 14-C-5-HT and 14-C-GABA was abolished at 0 degrees C. At 37 degrees C the accumulation of 14-C-GABA in the presence of ATP and magnesium reached a steady state after 20 min, while the accumulation of 14-C-5-HT reached a maximum after 2.5 min of incubation and then gradually declined. Osmotic lysis of the vesicles followed by sonication abolished the enhanced uptake of 14-C-GABA, 14-C-5-HT and 14-C-dopamine in the presence of ATP and magnesium. Determination of the endogenous contents of the vasicles revealed 14.6 pmoles per mg protein for 5-HT and 22.7 nmoles per mg protein for GABA. It is concluded that the caudate nucles preparation used in this study contains not only dopamine-storing vesicles able to take up biogenic amines but also GABA-containing vesicles which take up GABA by an ATP-magnesium-dependent process.