Adenylyl Cyclase Activity Mediated by β -Adrenoceptors in Immortalized Human Trabecular Meshwork and Non-Pigmented Ciliary Epithelial Cells

Abstract

Non-pigmented ciliary epithelial (NPE) and trabecular meshwork (TM) cells are important in maintaining normal aqueous humor dynamics through the inflow and outflow routes, respectively. The current studies were undertaken to evaluate the ability of several β-adrenergic receptor agonists to stimulate various antagonists to inhibit cAMP production in cultured immortalized human TM and NPE cells using an automated enzyme immunoassay. Isoproterenol was the most potent agonist in both the NPE and TM cells. The rank order of potency of agonists in NPE and TM cells, respectively, was: isoproterenol [EC₅₀ = 37 and 66 nM] > epinephrine [EC₅₀ = 112 and 526 nM] > albuterol [EC₅₀ = 426 and 785 nM] > norepinephrine [EC₅₀ = 3 and > 10 μM] > phenylephrine [EC₅₀ > 10 μM for both] = dopamine [EC₅₀ > 10 μM for both](n = 3-19). The isoproterenol-induced cAMP production was inhibited by various antagonists with the following rank order of potency in NPE and TM cells, respectively: propranolol [K_i = 0.2 and 0.3 nM] = ICI-118551 [K_i = 0.5 and 0.4 nM] > levobunolol [K_i = 1.1 and 2.1 nM] > levobetaxolol [K_i = 13 and 14 nM] = racemic betaxolol [K_i = 43 and 19 nM] > dextrobetaxolol [K_i = 2705 and 1980 nM] > atenolol [K_i > 4000 nM for both] (n = 3-7). These detailed pharmacological studies using a variety of agonists and antagonists further supported the presence of β₂-adrenergic receptors in immortalized human NPE and TM cells.