Effects of unoprostone and endothelin 1 on L-type channel currents in human trabecular meshwork cells

The trabecular meshwork (TM) is a smooth muscle-like tissue with contractile properties and by this mechanisms involved in the regulation of aqueous humor outflow. Isopropyl unoprostone (Rescula, Novartis Ophthalmics), a synthetic docosanoid, reduces intraocular pressure in glaucoma patients and normal subjects. In isolated TM strips, unoprostone reduces TM contractility in the presence of endothelin 1 (ET-1). However, the signal transduction pathway of unoprostone still remains unclear. Since L-type channel currents are known to influence the contractility of TM, we examined the effects of unoprostone and ET-1 on L-type channel currents of TM cells.

The effects of unoprostone, ET-1 and the tyrosine kinase inhibitor herbimycin A on L-type channel currents of cultured human TM cells were investigated using the perforated patch configuration of the patch-clamp technique.

Application of ET-1 had no effect on L-type channel currents. Unoprostone led to a dose-dependent reduction of control currents. The effect of unoprostone is independent of ET-1. After preincubation of cells with herbimycin A, unoprostone had no effect on the L-type channel current amplitude. Human TM cells preincubated with herbimycin A showed a reduced current density compared with control cells. Both substances, unoprostone and herbimycin A, increased the inactivation time constant of L-type channel currents.

We conclude that unoprostone reduces the activity of L-type Ca2+ channels. This effect seems to be independent of ET-1. The signal transduction pathway seems to be mediated by tyrosine kinases.