DOPAMINE D-4 RECEPTOR ISOFORM MESSENGER-RNA AND PROTEIN ARE EXPRESSEDIN THE RAT CORTICAL COLLECTING DUCT

We reported previously [Am. J. Physiol. 271 (Renal Fluid Electrolyte P hysiol. 40): F391-F400, 1996] that dopamine inhibits vasopressin (AVP) -dependent water permeability and Na+ transport in the rat cortical co llecting duct (CCD) apparently through a D-4 dopamine receptor. The pr esent experiments used RT-PCR of total RNA extracted from microdissect ed rat CCD to determine whether the D-4 and D-1A dopamine receptor iso forms are expressed. Specific primers were used to amplify three regio ns of the D-4 cDNA. All three gave products with 98-100% nucleotide id entity to the known rat D-4 sequence; however, there was an extra 6-bp insert at the 3' end of the second transmembrane region that was iden tical to the human and mouse sequences but which had not been document ed in the rat sequence. Dq receptor protein was also localized exclusi vely to the CCD and medullary collecting ducts by immunohistochemistry . Two regions of the D1A dopamine receptor message were also amplified by RT-PCR of RNA from rat CCD and were verified by sequencing and imm unohistochemistry. We conclude that both D-4 and D1A dopamine receptor s are expressed in the rat CCD, but the physiological effects are attr ibutable to a D-4 receptor.