Release of amines from acidified stores following accumulation by Transport‐P

Abstract

1 Transport-P is an uptake process for amines in peptidergic neurones of the hypothalamus. It diers from other uptake processes by its anatomical location in post-synaptic neurones, its functional properties and by the structure of its ligands. Transport-P accumulates amines in intracellular vesicles, derives its energy from the electrochemical proton gradient and is linked to vacuolar-type ATPase (V-ATPase). Transport-P is blocked by antidepressants. We have now studied the release of amines following uptake by Transport-P in a cell line of hypothalamic peptidergic neurones. 2 Release of prazosin was not inhibited by the antidepressant desipramine; as Transport-P is blocked by desipramine, this indicated that amines are released by a mechanism which is independent of Transport-P. 3 Release of prazosin was sensitive to temperature and conformed to the Arrhenius equation. Release was minimal in the range 0 ± 258C but accelerated exponentially at higher temperatures up to 338C. The activation energy for the release of prazosin is 83.1 kJ mol 71, corresponding to a temperature quotient (Q 10 ) value of 3. 4 Release was accelerated by the organic base chloroquine, the ionophore monensin, ba®lomycinA1 which inhibits V-ATPase and by increasing extracellular pH. Thus, retention of prazosin requires an intracellular proton gradient which is generated by V-ATPase. 5 Fluorescence microscopy demonstrated that release of BODIPY FL prazosin was temperature dependent and was accelerated by chloroquine and monensin. 6 Thus, following uptake by Transport-P, amines are accumulated in acidi®ed intracellular stores. Their retention in peptidergic neurones requires intracellular acidity. The amines are released by a temperature-dependent process which is resistant to antidepressants.