[3H]domperidone binding to the kidney inner medullary collecting duct dopamine-2K (DA2K) receptor

T Huo and DP Healy

Department of Pharmacology, Mount Sinai School of Medicine, City University of New York, New York.

Previous studies by our laboratory have indicated that inner medullary collecting ducts (IMCDs) express a novel dopamine (DA) receptor, designated DA2K, that is linked to stimulation of prostaglandin E2 production. This receptor has a distinct pharmacological profile and is similar in size, but not homologous to, the brain D2 receptor. Because the DA2-selective antagonist domperidone blocks DA-mediated stimulation of prostaglandin E2 production in IMCD cells, we utilized [3H]domperidone to study the binding characteristics of the DA2K receptor in IMCD cells. [3H]Domperidone binding was saturable and best fit to a single high density site (KD, 57.6 +/- 10.5 nM; Bmax, 14.9 +/- 2.7 pmol/mg protein). The specificity of [3H]domperidone binding in IMCD cells was verified by competition analysis with a variety of dopaminergic and nondopaminergic agents. Dopaminergic drugs were less potent competitors for [3H]domperidone binding in IMCD cells than previously reported for brain DA receptors, but the rank order was consistent with the labeling of a DA receptor [antagonists: domperidone greater than spiperone greater than haloperidol greater than Sch 23390 much greater than (-)-sulpiride; agonists: norapomorphine greater than fenoldopam much greater than dopamine = quinpirole], and was better correlated with the pharmacological profile for the brain D2 receptor than the brain D3 receptor. In addition, quinpirole, the most D3- selective ligand currently available, did not compete for [3H]domperidone binding in IMCD cells. These results add further support to the existence of a novel high density DA receptor, DA2K, expressed in IMCD cells.

Volume 258, Issue 2, pp. 424-428, 08/01/1991
Copyright © 1991 by American Society for Pharmacology and Experimental Therapeutics