EXPRESSION OF THE D-2 SUBFAMILY OF DOPAMINE-RECEPTOR GENES IN KIDNEY

The D-2, D-3, and D-4 dopamine receptors cloned from brain correspond to the classically described ''D-2'' receptors. Although radioligand binding and biochemical and functional studies have demonstrated the presence of D-2-like receptors in the kidney, the expression of D-2, D-3, or D-4 receptor genes has not been conclusively demonstrated in the kidney. Since Northern blot analysis may have precluded demonstration of dopamine receptor mRNAs because of their relative low abundance, the expression of the D-2long and D-3 receptor genes was studied by reverse transcription-polymerase chain reaction (RT-PCR). We were able to amplify PCR products of the predicted size using mRNA from glomeruli, proximal tubules, outer medulla, inner medulla, and renal microvessels from normotensive Wistar-Kyoto rats (WKY). Specificities of the amplified products were confirmed by restriction analysis and by sequencing the D-2long product and Southern blotting the D-3 product. Because some studies have suggested that D-2-like receptor actions may be different between WKY and spontaneously hypertensive rats (SHR), similar studies were performed in this rat strain. In the SHR, as in WKY, PCR products of the predicted size were amplified, and restriction enzyme digestion patterns were as predicted from the cDNA sequence. The PCR-generated cDNA from the glomeruli of SHR was subcloned and sequenced and was revealed to be identical to the D-2long receptor cDNA from WKY. We conclude that the D-2long and D-3 receptor genes are expressed in specific regions of the kidney including the glomeruli. No differences in the sequence of the D-2long receptor cDNA in part of the 3rd cytoplasmic loop were noted between WKY and SHR. These studies do not rule out the possibility that mutations in other segments of the receptor exist in the SHR.