[3H]-Spiroperidol labels dopamine receptors in membranes from rabbit mesenteric artery

Summary The potent dopamine receptor antagonist [³H]-spiroperidol was used to label binding sites in a membrane fraction derived from rabbit mesenteric artery which had characteristics expected for dopamine receptors. The binding was of high affinity with an equilibrium dissociation constant (K_D) of 13.1 nM; it was saturable with 110 fmol of [³H]-spiroperidol bound/mg protein at maximal occupancy of the sites. Binding at 37° C was rapid and readily reversible with rate constants of 0.0154 nM^–1 min^–1 and 0.114 min^–1 for forward and reverse reaction, respectively. Dopamine receptor antagonists were about 100–200 times more potent than -adrenolytic drugs in competing for the [³H]-spiroperidol binding sites and dopamine was much more potent than (–)-noradrenaline, adrenaline, (–)-isoprenaline, clonidine or serotonin. It is concluded that in a membrane fraction of the rabbit mesenteric artery there exist binding sites for [³H]-spiroperidol indistinguishable from dopamine receptors. Thus the present results support the view that in vascular smooth muscle there exist specific dopamine receptors.This work was supported by the Deutsche Forschungsgemeinschaft