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

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.