Cloning and characterization of the opossum kidney cell D1 dopamine receptor: expression of identical D1A and D1B dopamine receptor mRNAs in opossum kidney and brain.

Opossum kidney cells are an established epithelial cell line which is often studied as a physiological model system of renal proximal tubule function, and which has also been shown to possess dopamine receptors. To identify dopamine receptor subtypes present in renal tissue, as well as to explore the usefulness of opossum kidney cells for the study of D1 dopamine receptors and renal dopaminergic physiology, we have undertaken the cloning and characterization of the dopamine receptor expressed in this cell line. In the brains of rats and humans, two different subtypes of D1 dopamine receptors, D1A and D1B, have recently been characterized. The OK cell D1 receptor message is 4500 bp long and exhibits extensive homology with the rat and human D1A subtypes of dopamine receptors. Pharmacological experiments were performed on COS-7 cell membranes transiently transfected with this cDNA. Binding properties were compared with those reported for OK cell membranes, and comparison experiments were performed in parallel with the human D1A expressed transiently in the same system. Molecular techniques including Northern blotting, in situ hybridization, and RNase protection analysis were used to study the expression pattern of the OK cell D1 receptor message. Expression of both D1A and D1B subtypes was detected in both the opossum brain and the opossum kidney, however, the OK cell line expresses exclusively the D1A receptor subtype.