Specific prostaglandin E2 binding sites in isolated rat glomeruli: evidence for glomerular PGE receptors

Stimulation of adenylate cyclase by prostanoids in isolated glomerulus has been demonstrated previously suggesting the interaction of these lipids with specific receptors. In the present study, the presence and characteristics of these purported specific PGE receptors has been evaluated. Binding studies were performed with both [3H]PGE1 and [3H]PGE2 in isolated rat glomeruli obtained by standard sieving methods. Radioligand binding was demonstrated to be both reversible and saturable. The equilibrium dissociation constant (Kd) value for PGE2 was 14.3 nM and maximum number of receptor sites (Bmax) was 81.4 fmol/mg protein. Similar values were obtained for PGE1. Competitive binding studies performed with [3H]PGE1 in the presence of various prostanoids revealed a common binding site for PGE1, PGE2 and 16,16-dimethyl PGE2. The relative potency for displacement of [3H]PGE1 binding of various prostanoids was PGE1 = 16,16-dimethyl PGE2 = PGE2 much greater than T X B2 = PGD2 much greater than PGF 2 alpha greater than 6-keto-PGF 1 alpha. Hill plot analysis of both [3H]PGE1 and [3H]PGE2 binding studies showed a simple non-cooperative bimolecular interaction between PGE and a single receptor population. Finally, a dose-dependent stimulation of adenylate cyclase was noted with various concentrations of PGE1 in a membrane preparation derived from a similar glomeruli preparation. Thus the results of these studies provide evidence for the presence of specific PGE receptors in the rat glomerulus.