Inhibition of Endothelin-1 and KCl-Induced Increase of [Ca 2+ ] i by Antiglaucoma Drugs in Cultured A7r5 Vascular Smooth-Muscle Cells

Abstract

Over contraction of vascular smooth muscle may result in ischemia to ocular neuronal cells and deteriorate the glaucoma. The purpose of this study was to investigate the inhibitory effects of various commercial antiglaucoma drugs including brimonidine, dipivefrin, betaxolol, timolol, levobunolol, carteolol, brinzolamide, dorzolamide, unoprostone, latanoprost, pilocarpine, and preservative benzalkonium chloride on endothelin-1(ET-1) and KCl-induced increase of intracellular free Ca²⁺ ([Ca²⁺]_i) in cultured rat A7r5 vascular smooth muscle cells. These drugs were diluted from original concentrations to 1/100, 1/1000, and 1/10000. [Ca²⁺]_i mobility was analyzed by spectrofluorometry after loading with fura-2-AM. Betaxolol, timolol, levobunolol, and carteolol were found to inhibit KCl-induced release of [Ca²⁺]_i in a dose-dependent manner. High concentrations of betaxolol, timolol, levobunolol, carteolol, and unoprostone also inhibited ET-1-induced increase of [Ca²⁺]_i in A7r5 cells. However, ET-1- and KCl-induced increase of [Ca²⁺]_i was not diminished by other drugs including brimonidine, dipivefrin, brinzolamide, dor- zolamide, latanoprost, pilocarpine, and benzalkonium chloride. These results indicate that high concentrations of unoprostone and beta-adrenergic blocking agents including betax- olol, timolol, levobunolol, and carteolol may inhibit ET-1-induced increase of [Ca²⁺]_i. The mechanism may be mediated by inhibition of extracellular calcium influx via blocking of L-type voltage-dependent Ca²⁺ channel in A7r5 cells.