Binding of [3H]SCH 23390 to dopamine D-1 receptors in rat retina in vitro.

[3H]SCH 23390 binding was examined in membranes of rat retina. The binding was saturable with a dissociation constant of 0.2 nM and the maximum number of binding sites was 236 +/- 74 fmol/mg protein. The pharmacology of [3H]SCH 23390 binding indicated that the binding was specific for a dopamine D-1 receptor because the binding was preferentially inhibited by D-1-selective agonists and antagonists but not by dopamine D-2-selective agonists and antagonists. The same membrane preparations were used to characterize the dopamine D-2 receptor binding as measured with [3H]spiperone and the amount of binding sites was found to be similar to the amount of D-1 sites. It is concluded that [3H]SCH 23390 is a useful tool to examine dopamine D-1 receptors in the retina.