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

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 (KD) 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 degrees C was rapid and readily reversible with rate constants of 0.0154nM-1 min-1 and 0.114min-1 for forward and reverse reaction, respectively. Dopamine receptor antagonists were about 100--200 times more potent than alpha-adrenolytic drugs in competing for the [3H]-spiroperidol binding sites and dopamine was much more potent than (-)-noradrenaline, (-)-isoprenaline, clonidine or serotonin. It is concluded that in a membrane fraction of the rabbit mesenteric artery there exist binding sites for [eH]-spiroperidol indistinguishable from dopamine receptors. Thus the present results support the view that in vascular smooth muscle there exist specific dopamine receptors.