Differential effects of prostaglandin E₂-sensitive receptors on contractility of human ocular cells that regulate conventional outflow

PURPOSE. The goal of this study was to functionally compare prostaglandin E₂ (PGE₂)-sensitive receptors in human primary cells involved in conventional outflow. METHODS. The expression profile of prostaglandin (PG) receptors in primary cultures of human trabecular meshwork (TM) and Schlemm's canal (SC) cells were determined by quantitative-PCR. The functional activities of endogenous PGE₂-sensitive receptors were evaluated using subtype-selective agonists and antagonists with cell impedance technology. RESULTS. Agonist-sensitive EP₁, EP₂, and EP₄ receptors were present in TM cells, all increasing cell stiffness (or contractility) in a dose-dependent manner. Rank order of efficacy (E_max) for agonists in TM cells were EP1 greater than EP₂ greater than EP₄ with EC₅₀ 1.1 μM, 0.56 μM, and 0.1 μM, respectively, and no functional EP₃ receptors were found. Of the four EP receptor subtypes active in SC cells, EP₁ and EP₃ receptor activation increased cell stiffness, while EP₂ and EP₄ agonists dose-dependently decreased cell stiffness 47% and 23% with EC50 values of 170 nM and 69 nM, respectively. Consistent with these observations, the Rho kinase inhibitor Y-27632 decreased cell impedance (stiffness) of TM and SC cells (~60%), while Rho GTPase activator thrombin caused cell impedance to increase in both cell types (168%-190%). CONCLUSIONS. Cell impedance positively correlates with cellular stiffness/contractility. Because EP_2/4 receptors caused decreased cell stiffness in SC, but not in TM cells, both receptors appear to mediate IOP lowering via changes in SC cell stiffness in the conventional outflow pathway.