Functional Pharmacological Evidence for EP 2 and EP 4 Prostanoid Receptors in Immortalized Human Trabecular Meshwork and Non-Pigmented Ciliary Epithelial Cells

Abstract

The aim of these studies was to characterize the molecular pharmacology of the prostanoid receptors positively coupled to stimulation of adenylyl cyclase activity in immortalized human trabecular meshwork (TM-3) cells and to compare these results with that of the receptors in immortalized human nonpigmented epithelial (NPE) cells. In general, the TM-3 and NPE cells showed a similar profile with respect to their responses to various prostaglandin (PG) receptor agonists. The rank order of potency (EC₅₀; means ± SEM) for these compounds in the TM-3 cells was: PGE₂ (124 ± 21 nM) > 13,14-dihydro-PGE₁ (430 ± 110 nM) = PGE₁ (522 ± 345 nM) > 11-deoxy-PGE₁ (1063 ± 118 nM) = 16,16- dimethyl-PGE₂ (1776 ± 460 nM) = butaprost (1920 ± 527 nM) >> PGD₂ = PGI₂ = PGF_2α (n = 3 - 12). While the agonist profile indicated the presence of EP₂ receptors, the effects of the EP₄ receptor antagonists suggested the additional expression of EP₄ receptors in both of these cells. Thus, the EP₄ receptor antagonist, AH23848B, at a concentration of 30 μM, caused a dextral shift in the PGE₂ concentration-response curves in both TM-3 and NPE cells coupled with a 20-28% decrease in the maximal response of PGE₂, indicating apparent noncompetitive antagonism profiles. The antagonist potency of AH23848B in these cells was: K_b = 38.4 ± 14.8 μM and 23.5 ± 4.5 μM;-log K_b = 4.7. The other EP₄ receptor antagonist, AH22921 (-log K_b = 4.1 - 4.7), was weaker than AH23848B. Taken together, these pharmacological studies have shown than TM-3 and NPE cells apparently contain functional EP₂ and EP₄ prostanoid receptors positively coupled to adenylyl cyclase.