Abstract
Purpose: :
The large-conductance calcium-activated potassium (BKca) channels mediate the nitric oxide (NO)-induced increase in outflow facility and decrease in trabecular meshwork (TM) cell volume. This NO-induced reduction in TM cell volume is mediated through a signal transduction pathway involving soluble guanylate cyclase (sGC), cGMP generation and protein kinase G (PKG). In this study we investigate the ability of a direct activator of the BKca channel, NS1619, to increase outflow facility and decrease TM cell volume.
Methods: :
Outflow facility was measured using an anterior segment organ perfusion system. Low passage TM cells were loaded with Calcein AM and visualized using a confocal microscope. Images were taken of TM cells that were treated with or without: DETA-NO, NS1619, hypotonic medium (30% water). Cell volumes were quantified from confocal image stacks using NIH ImageJ software.
Results: :
Following a steady basal outflow facility (0.4199+0.0071 ul/min/mmHg) (mean+SEM) a bolus administration of NS1619 (30uM) resulted in a significant increase in outflow facility (0.7816+0.0528 ul/min/mmHg). Outflow facility remained elevated for 3 hours post drug administration before returning to baseline values. Additionally, NS1619 dose-dependently decreased TM cell volume and prevented a hypotonic-induced TM cell volume increase. Finally, exposure to either the NO donor DETA-NO or NS1619 resulted in decreases in TM cell volume, but when administered in combination, produced no additional cell volume decrease.
Conclusions: :
These data demonstrate the ability of NS1619, a direct activator of the BKca channel, to increase outflow facility and decrease TM cell volume in a dose-dependent manner. Additionally, NS1619 when administered with a hypotonic shock, attenuated the hypotonic-induced increases in TM cell volume, further implicating the BKca channel in TM cell regulatory volume decrease. The inability of DETA-NO and NS1619 to cause greater decreases in TM cell volume when compared with NS1619 or with DETA-NO alone, suggest that their combined effects are not additive. Taken together, our data suggest that activators of the BKca channel, like NS1619, may have ocular hypotensive properties.
Keywords: trabecular meshwork • outflow: trabecular meshwork • ion channels