Binding of [3H]-dopamine to human lymphocytes: possible relationship to neurotransmitter uptake sites

Freshly isolated human lymphocytes from 11 healthy subjects had specific binding sites for dopamine which were dependent on time, temperature and sodium, and appeared to follow Michaelis-Menten kinetics. The apparent affinity constant (KD) of human lymphocytes for dopamine and the maximal number of binding sites (Bmax) were 109 +/- 21 nM and 2.66 +/- 1.75 pmol/10(7) cells, respectively. Dopamine binding was markedly affected by cocaine (IC50 = 150 nM) and other inhibitors of biogenic amine uptake. The relatively high potency of cocaine in competing for dopamine binding suggested that human lymphocytes may serve as a readily accessible model to detect changes in the neuronal uptake of dopamine and perhaps other monoamine neurotransmitters.