title: G protein-coupled prostaglandin receptor modulates conductive Na+ uptake in lung apical membrane vesicles.
abstract: Because G protein-regulated cation channels in type II pneumocytes constitute the most likely pathway for alveolar Na+ entry, we explored the hypothesis that a G protein-coupled prostaglandin (PG) E2 receptor controls perinatal lung alveolar Na+ transport. [3H]PGE2 binding to the alveolar apical membrane was trypsin sensitive and showed a rank order of competitive inhibition: PGE2 = PGE1 > PGD2 > PGF2 alpha. Kinetic analysis demonstrated both high-affinity [dissociation constant (KD) = 2.1 +/- 0.7 nM; maximal binding (Bmax) = 27 +/- 7 fmol/mg protein] and low-affinity (KD = 28 +/- 2 nM; Bmax = 265 +/- 29 fmol/mg protein) binding sites. Modulation of high-affinity GTPase activity identified a similar potency order (IC50 = 11 mM for PGF2 alpha vs. 10-50 microM for other PGs), suggesting that the receptors are G protein coupled. Finally, 1 microM PGE2 (approximately IC25) increased conductive 22Na+ uptake into membrane vesicles only in the presence of 100 microM intravesicular GTP. The KD value for the high-affinity binding site together with the rank order of PG effect on ligand binding and G protein function places this PG receptor in the EP3 subtype, whereas Na+ uptake studies suggest that it helps maintain perinatal lung Na+ homeostasis.
authors.affiliation: Department of Child Health, Ninewells Hospital and Medical School, University of Dundee, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Mukhopadhyay
authors.forename: A K
authors.initials: AK
authors.lastname: Dutta-Roy
authors.forename: G K
authors.initials: GK
authors.lastname: Fyfe
authors.forename: R E
authors.initials: RE
authors.lastname: Olver
authors.forename: P J
authors.initials: PJ
authors.lastname: Kemp
mesh_terms: D000818:Animals; D001665:Binding Sites; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D006168:Guinea Pigs / Q000196:embryology; D008168:Lung / Q000378:metabolism*; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D012964:Sodium / Q000493:pharmacokinetics*; D013379:Substrate Specificity / Q000502:physiology
chemical_list: D011982:Receptors, Prostaglandin; D012964:Sodium; D019204:GTP-Binding Proteins; D015232:Dinoprostone