Dopamine receptor binding regulated by guanine nucleotides

Guanosine triphosphate (GTP) and diphosphate nucleotides decrease the binding of the agonist ligands [³H]apomorphine and [³H]ADTN to dopamine receptors in the rat corpus striatum with half maximal reduction of binding at 5 μM. These nucleotides also reduce agonist inhibition of the antagonist [³H]spiroperidol binding to dopamine receptors without affecting total [³H]spiroperidol binding. Guanosine monophosphate and adenine nucleotides display negligible influence on dopamine receptor binding. GTP reduces the affinity of [³H]apomorphine binding with no effect on the maximal numbers of binding sites.