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

Transport‐P is an uptake process for amines in peptidergic neurones of the hypothalamus. It differs 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. 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. Release of prazosin was sensitive to temperature and conformed to the Arrhenius equation. Release was minimal in the range 0 – 25°C but accelerated exponentially at higher temperatures up to 33°C. The activation energy for the release of prazosin is 83.1 kJ mol −1 , corresponding to a temperature quotient (Q 10 ) value of 3. Release was accelerated by the organic base chloroquine, the ionophore monensin, bafilomycinA1 which inhibits V‐ATPase and by increasing extracellular pH. Thus, retention of prazosin requires an intracellular proton gradient which is generated by V‐ATPase. Fluorescence microscopy demonstrated that release of BODIPY FL prazosin was temperature dependent and was accelerated by chloroquine and monensin. Thus, following uptake by Transport‐P, amines are accumulated in acidified intracellular stores. Their retention in peptidergic neurones requires intracellular acidity. The amines are released by a temperature‐dependent process which is resistant to antidepressants.British Journal of Pharmacology (2001) 132 , 851–860; doi: 10.1038/sj.bjp.0703872