LIGAND-BINDING SPECIFICITIES OF THE 8 TYPES AND SUBTYPES OF THE MOUSEPROSTANOID RECEPTORS EXPRESSED IN CHINESE-HAMSTER OVARY CELLS

1 Eight types and subtypes of the mouse prostanoid receptor, the prost aglandin D (DP) receptor, the prostaglandin F (FP) receptor, the prost aglandin I (IP) receptor, the thromboxane A (TP) receptor and the EP1, EP2, EP3 and EP4 subtypes of the prostaglandin E receptor, were stabl y expressed in Chinese hamster ovary cells. Their ligand binding chara cteristics were examined with thirty two prostanoids and their analogu es by determining the K-i values from the displacement curves of radio ligand binding to the respective receptors. 2 The DP, IP and TP recept ors showed high ligand binding specificity and only bound their own pu tative ligands with high affinity such as PGD(2), BW245C and BW868C fo r DP, cicaprost, iloprost and isocabacyclin for IP, and S-145, I-BOP a nd GR 32191 for TP. 3 The FP receptor bound PGF(2 alpha) and fluproste nol with K-i values of 3-4 nM. In addition, PGD(2), 17-phenyl-PGE(2), STA(2), I-BOP, PGE(2) and M&B-28767 bound to this receptor with K-i va lues less than 100 nM. 4 The EP1 receptor bound 17-phenyl-PGE(2), sulp rostone and iloprost in addition to PGE(2), and PGE(1), with K-i value s of 14-36 nM. 16,16-dimethyl-PGE(2) and two putative EP1 antagonists, AH-6809 and SC-19220, did not show any significant binding to this re ceptor. M&B-28767, a putative EP3 agonist, and misoprostol, a putative EP2/EP3 agonist, also bound to this receptor with K-i values of 120 n M. 5 The EP2 and EP4 receptors showed similar binding profiles. They b ound 16,16-dimethyl PGE(2) and 11-deoxy-PGE(1) in addition to PGE(2) a nd PGE(1). The two receptors were discriminated by butaprost, AH-13205 and AH-6809 that bound to the EP2 receptor but not to the EP4 recepto r, and by 1-OH-PGE(1) that bound to the EP4 but not to the EP2 recepto r. 6 The EP3 receptor showed the broadest binding profile, and bound s ulprostone, M&B-28767, GR63799X, 11-deoxy-PGE(1), 16,16-dimethyl-PGE(2 ) and 17-phenyl-PGE(2), in addition to PGE(2) and PGE(1), with K-i val ues of 0.6-3.7 nM. In addition, three IP ligands, iloprost, carbacycli n and isocarbacyclin, and one TP ligand, STA(2), bound to this recepto r with K-i values comparable to the K-i values of these compounds for the IP and TP receptors, respectively. 7 8-Epi-PGF(2 alpha) showed onl y weak binding to the IF, TP, FP, EP2 and EP3 receptor at 10 mu M conc entration.