Alterations of intracellular calcium in human non-pigmented ciliary epithelial cells of the eye.
The ciliary epithelium of the eye is thought to be responsible for the active production of aqueous humor. The role of hormones and neuropeptides in mediating this process is unclear. Alterations in intracellular calcium in response to several hormones were assayed by fluorometric detection utilizing Quin2 in human SV-40 transformed non-pigmented ciliary epithelial cells grown in monolayer culture. A dose-dependent increase in intracellular calcium was found for the following drugs, which are given with their respective EC50 values: carbachol (15.7 +/- 4 microM), ATP (1.67 +/- 0.4 microM), arginine vasopressin (52 +/- 14 nM), bradykinin (2.4 +/- 0.7 nM), histamine (0.7 +/- 0.1 microM), and angiotensin II (6.4 +/- 1 nM). The following increases in calcium levels above typical resting levels of 45.9 +/- 4.6 nM were observed: 30% (0.1 microM angiotensin II), 50% (0.1 microM bradykinin, 2 microM arginine vasopressin), 100% (10 microM histamine), and 150% (1 mM carbachol, 10 microM ATP). Dopamine, KCl, phorbol esters, propranolol, epinephrine, and norepinephrine failed to increase intracellular calcium levels. The mobilization of intracellular calcium was unaffected by changes in the pH of the extracellular medium (over the pH range of 7.6 to 6.9) induced by glacial acetic, sulfuric or hydrochloric acids. Phosphatidic acid, however, did cause an elevation in intracellular calcium and is consistent with its putative role as an ionophore in other non-excitable exocrine tissues. These studies suggest a role for the hormonally induced mobilization of intracellular calcium which may underlie the secretion of aqueous humor by these cells.