Molecular and structural differences between rat brain D-1 and renal DA-1 dopamine receptors

Renal DA-1 dopamine receptors in proximal tubules (PTs) of the Wistar-Kyoto (WKY) rat display pharmacological binding properties which are different from central nervous system (CNS) striatal D-1 dopamine receptors. In general, the renal DA-1 receptors display affinity binding values of dopaminergic drugs which are 6-36-fold less than those seen for brain D-1 receptors. The renal and brain DA receptors also displayed differential sensitivity toward the alkylating agent, N-ethylmaleimide (NEM). Inactivation of 50% of DA-1 renal receptors was achieved at lower concentrations of NEM (5.2 μM) relative to brain D-1 receptors (140 μM). Western blot analyses of rat pituitary GH₄C₁ cells, transfected with human CNS D-1 receptor cDNA, with human anti-D-1 dopamine receptor antiserum, detected a single polypeptide with M(r) of 66 kDa. In PTs, a specific polypeptide of higher molecular weight (M(r) = 72 kDa) was seen. Surprisingly, in rat striatal membranes, the D-1 antiserum failed to detect any proteins within this molecular weight range. Photoaffinity labeling studies with a DA-1 selective photoligand, identified the identical protein by autoradiography and Western blots in kidney, but not in striate. Together, these data indicate that renal DA-1 dopamine receptors have distinct molecular properties relative to brain D-1 dopamine receptors.