Effect of diuretics, channel modulators and signal interceptors on contractility of the trabecular meshwork

Measurements of isometric tension were performed on isolated trabecular meshwork (TM) and ciliary muscle (CM) strips of the bovine eye. Anterior segments of bovine eyes with well-preserved TM were perfused to measure outflow rate. (1) Bumetanide (10(-4) mol/l) and hydrochlorothiazide (10(-4) mol/l) did not change the contractility of TM and CM strips in the presence or absence of carbachol. Ethacrynic acid dose-dependently relaxed TM and CM strips precontracted either by carbachol or endothelin. (2) Cytochalasin D totally relaxed TM and CM strips precontracted by carbachol. The outflow rate almost doubled after application of cytochalasin D. (3) The effects of various modulators of K+ and Ca2+ channels are summarized. Carbachol and endothelin are postulated to modify nonselective cation channels. An effective blocker of nonselective cation channels (flufenamic acid) relaxed TM and CM precontracted by carbachol or endothelin. These relaxing effects were independent of the relaxing effects of ethacrynic acid and isosorbide dinitrate. (4) Evidence for the presence of various transporters and receptors in TM cells is summarized. (5) The TM per se is a contractile element which is involved in the regulation of aqueous humor outflow. The contractility of TM and CM cells is differently modulated.