ATP-regulated neuronal catecholamine uptake: A new mechanism

Abstract

Uptake of the catecholamines (CA), dopamine (DA) and norepinephrine (NE) into synaptosomes prepared from rat and bovine brains was potentiated by ATP (from 0.1 to 5.0 mM) in a dose-dependent manner. Other nucleotides, particularly the nonhydrolyzable ATP analogs β, γ-imidoadenosine-5′-triphosphate (AMP-PNP) and β, γ-methyladenosine-5′-triphosphate (AMP-PCP) also potentiated [ 3H]DA and [ 3H]NE uptake. Several endogenous 5′-nucleotide triphosphates (e.g. GTP, UTP and CTP) potentiated [ 3H]CA uptake, but were less effective than ATP. Among the ATP metabolites, only ADP potentiated uptake whereas AMP and adenosine did not. [ 3H] Dopamine uptake measured in Krebs bicarbonate buffer had a Km of 2.1 μM and a V max of 163.9 pmol/mg prot./min. In presence of ATP, [ 3H]DA uptake had much higher affinity (Km = 0.56 μM) and larger capacity (V max = 333 pmol/mg prot./min) than uptake in absence of added ATP. Furthermore, [ 3H]DA uptake in presence of ATP had faster rate of uptake, and was independent of temperature while in absence of added ATP it was temperature-dependent. This ATP-dependent [ 3H]DA uptake was retained by synaptosomal ghosts that were obtained after lysing the striatal synaptosomes and removing their contents of synaptic vesicles and mitochondria. It is proposed that, in addition to the carrier-mediated (neuronal) uptake of CA, there is neuronal uptake that is regulated by ATP and inhibited by cocaine, which may be more relevant for terminating the synaptic action of CA because of its faster rate of uptake and larger capacity.