Influence of muscarinic agonists and tyrosine kinase inhibitors on L-type Ca2+ channels in human and bovine trabecular meshwork cells

Trabecular meshwork (TM), a smooth muscle-like tissue with contractile prop erties, is involved in the regulation of aqueous humor outflow. However, li ttle is known about the regulation of Ca2+ influx in trabecular meshwork ce lls, We investigated the influence of acetylcholine and tyrosine kinases on Ca2+ conductances of bovine TM (BTM) and human TM (HTM) cells using the pe rforated-patch configuration of the patch-clamp technique and measurements of intracellular free Ca2+ ([Ca2+](i)). Depolarization of the cells in the presence of 10 mM Ba2+ or Ca2+ led to an activation of inward currents at p otentials positive to -30 mV with characteristics typical of L-type Ca2+ cu rrents: when using 10 mM Ba2+, maximal inward current and inactivation time constant (tau) increased: the L-type Ca2+ channel blocker nifedipine (1 mu M) reduced and the L-type Ca2+ channel agonist BagK8644 (5 mu M) enhanced maximal inward current. Acetylcholine (100 mu M) and carbachol (1 mu M) led to an increase in inwar d Ba2+ current Whereas application of the tyrosine kinase inhibitors genist ein (50 mu M) and lavendustin A (20 mu M) resulted in a decrease in inward current. The application of daidzein (10 mu M), an inactive analog of genis tein had no effect. Depolarization of the cells with 135 mM K+ or direct st imulation of L-type channels by application of BayK 8644 led to an increase in [Ca2+](i). Carbachol (1 mu M) induced an increase in [Ca2+](i) which wa s,, decreased by application of the tyrosine kinase inhibitor genistein (50 mu M). We conclude that HTM and BTM cells express voltage-dependent L-type Ca2+ channels that influence intracellular Ca2+ concentration and thus may modulate TM contractility. The activity of L-type Ca2+ currents is influen ced by muscarinic agonists and tyrosine kinases. (C) 2000 Academic Press.