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

Abstract

Dopamine-containing vesicles were isolated from the caudate nucleus of the pig by differential centrifugation and incubated with ¹⁴C-serotonin (¹⁴C-5-HT), ¹⁴C-gamma-aminobutyric acid (¹⁴C-GABA), ¹⁴C-dopamine or ¹⁴C-histamine. At 25°C the uptake of ¹⁴C-5-HT and ¹⁴C-GABA was enhanced by ATP and magnesium. The Km for the uptake of ¹⁴C-5-HT in the presence of ATP and magnesium was 0.67×10⁻⁶ M, that of ¹⁴C-GABA 1.33×10⁻⁴ M. ¹⁴C-Histamine was also taken up into the vesicles but its uptake was not influenced by ATP and magnesim. The ATP-magnesium-dependent uptake of ¹⁴C-5-HT and ¹⁴C-GABA was abolished at 0°C. At 37°C the accumulation of ¹⁴C-GABA in the presence of ATP and magnesium reached a steady state after 20 min, while the accumulation of ¹⁴C-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 ¹⁴C-GABA, ¹⁴C-5-HT and ¹⁴C-dopamine in the presence of ATP and magnesium. Determination of the endogenous contents of the vesicles 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.