Characteristics of [3H]sultopride binding to rat brain.

The binding of [3H]sultopride, a benzamide drug, to rat brain was investigated in vitro. Specific [3H]sultopride binding was observed in dopaminergic regions: striatum, nucleus accumbens, olfactory tubercle, substantia nigra, frontal cortex and anterior pituitary. Specific [3H]sultopride binding to striatum was saturable and had one high affinity binding site with a KD of 5.8 nM and a total density of receptors 25.7 pmol/g. [3H]Sultopride binding was stereoselectively displaced by (-)- and (+)-sultopride. Inhibition studies indicated that all neuroleptic drugs and dopamine were capable of displacing sultopride from its binding sites. A highly significant correlation was observed between IC50 values against [3H]sultopride and those against [3H]spiperone binding. Specific [3H]sultopride binding was highly dependent on the presence of sodium ions. The results suggest that the characteristics of sultopride binding sites seem to be similar to those of the D2-receptor labeled by spiperone and haloperidol. The sultopride binding site was highly dependent on the presence of sodium ions and may thus be characterized as a sodium-dependent D2-receptor.