Binding of [H-3] Sch23390 to a Nondopaminergic Site in Bovine Kidney

Binding of the D1 dopamine receptor antagonist [H-3]SCH23390 to bovine renal cortical membranes has been studied. Specific binding of [H-3]SCH23390 was saturable and reversible and stereoisomers of SCH23390 competed stereoselectively. In contrast, competition with the isomers of butaclamol was not stereoselective and dopamine failed to compete for the [H-3]SCH23390 binding site. The site is therefore not a D1 dopamine receptor. Competition studies with a very wide range of compounds failed to define the nature of the [H-3]SCH23390 binding sites in renal cortex whereas in parallel studies the characteristics of [H-3]SCH23390 binding in caudate nucleus were entirely consistent with those of D1 dopamine receptors. The nature of [H-3]SCH23390 binding in preparations of tubular and glomerular membranes was found to be virtually identical to those of crude renal cortical membranes indicating lack of compartmentation of these sites. Autoradiographic studies of [H-3]SCH23390 binding in bovine kidney showed significantly higher levels of binding sites in renal cortex compared with renal medulla and this was confirmed by direct ligand binding studies.