PURPOSE: Muscarinic agonists contract and tyrosine kinase inhibitors relax precontracted trabecular meshwork, a smooth muscle-like tissue involved in the regulation of aqueous humor outflow. The effect of tyrosine kinase inhibitors on membrane currents of cells stimulated by acetylcholine was examined. METHODS: Cells from bovine trabecular meshwork were studied using both the perforated patch-clamp technique with nystatin and the single-channel technique. RESULTS: Application of the tyrosine kinase inhibitor genistein (5 x 10(-5) M) on trabecular meshwork cells stimulated with acetylcholine resulted in a reversible increase in outward current to 578%+/-154% (n = 16) of the initial current level. The effect of genistein was dose dependent. Reversal potential was hyperpolarized by 15+/-3 mV (n = 9). Tyrphostin 51, a synthetic inhibitor of tyrosine kinases, had the same effect (433%+/-46%; n = 7). Daidzein, a nonactive structural analogue of genistein, had no effect (n = 4). The stimulation of outward current by tyrosine kinase inhibitors was blocked by substitution of tetraethylammonium (TEA+) for potassium, whereas the potassium channel blockers glibenclamide (K-ATP) and apamin (low-conductance calcium-activated potassium channel) had no effect. Blockage of the high-conductance calcium-activated potassium channel (maxi-K) by charybdotoxin or iberiotoxin (10(7) M) suppressed 86%+/-18% (n = 4) of the response. Depleting the cells of calcium did not have an effect on the current stimulated by genistein. In the excised inside-out configuration, open probability increased to 417%+/-39% (n = 3) after exposure to genistein. CONCLUSIONS: In trabecular meshwork, tyrosine kinase inhibitors activate maxi-K (K(Ca)) channels. Hyperpolarization caused by efflux of potassium could lead to the relaxation of trabecular meshwork by tyrosine kinase inhibitors.
PURPOSE: Muscarinic agonists contract and tyrosine kinase inhibitors relax precontracted trabecular meshwork, a smooth muscle-like tissue involved in the regulation of aqueous humor outflow. The effect of tyrosine kinase inhibitors on membrane currents of cells stimulated by acetylcholine was examined. METHODS: Cells from bovine trabecular meshwork were studied using both the perforated patch-clamp technique with nystatin and the single-channel technique. RESULTS: Application of the tyrosine kinase inhibitor genistein (5 x 10(-5) M) on trabecular meshwork cells stimulated with acetylcholine resulted in a reversible increase in outward current to 578%+/-154% (n = 16) of the initial current level. The effect of genistein was dose dependent. Reversal potential was hyperpolarized by 15+/-3 mV (n = 9). Tyrphostin 51, a synthetic inhibitor of tyrosine kinases, had the same effect (433%+/-46%; n = 7). Daidzein, a nonactive structural analogue of genistein, had no effect (n = 4). The stimulation of outward current by tyrosine kinase inhibitors was blocked by substitution of tetraethylammonium (TEA+) for potassium, whereas the potassium channel blockers glibenclamide (K-ATP) and apamin (low-conductance calcium-activated potassium channel) had no effect. Blockage of the high-conductance calcium-activated potassium channel (maxi-K) by charybdotoxin or iberiotoxin (10(7) M) suppressed 86%+/-18% (n = 4) of the response. Depleting the cells of calcium did not have an effect on the current stimulated by genistein. In the excised inside-out configuration, open probability increased to 417%+/-39% (n = 3) after exposure to genistein. CONCLUSIONS: In trabecular meshwork, tyrosine kinase inhibitors activate maxi-K (K(Ca)) channels. Hyperpolarization caused by efflux of potassium could lead to the relaxation of trabecular meshwork by tyrosine kinase inhibitors.
Authors: Félix Gil-Carrasco; Daniel Ochoa-Contreras; Marco A Torres; Jorge Santiago-Amaya; Fidel W Pérez-Tovar; Roberto Gonzalez-Salinas; Luis Nino-de-Rivera Journal: J Ophthalmol Date: 2018-07-19 Impact factor: 1.909
Authors: Jacques A Bertrand; Martin Schicht; W Daniel Stamer; David Baker; Joseph M Sherwood; Elke Lütjen-Drecoll; David L Selwood; Darryl R Overby Journal: Invest Ophthalmol Vis Sci Date: 2020-03-09 Impact factor: 4.799