Stimulatory Action of Ouabain, an Inhibitor of Na+,K+–ATPase on BKCa–Channel Activity in Human Retinal and Iris Pigment Epithelial Cells

Abstract

Abstract: : Purpose: To determine if there are any effects of ouabain on BK_Ca–channel activity in human retinal and iris pigment epithelial (IPE) cells. Methods: Effects of ouabain on BK_Ca–channel activity were investigated with the aid of the patch–clamp technique. Results: In whole–cell configuration, ouabain (10 µM) increased the amplitude of K⁺ outward current measured at the level of +50 mV. Ouabain–stimulated outward current was reversed by paxilline (1 µM) or iberiotoxin (200 nM), yet not by glibenclamide (10 µM) or apamin (200 nM). In cells challenged with hypotonicity (200 mOsm), ouabain was found to have no effect on K⁺ outward current. In cell–attached patches from human IPE cells, bath application of ouabain did enhance BK_Ca–channel activity without a change in single–channel amplitude. BK_Ca–channel activity in these cells could be enhanced by membrane stretch. However, ouabain did not modify BK_Ca–channel activity induced by membrane stretch. In addition, in inside–out patches, ouabain applied to the intracellular surface had no effect on BK_Ca–channel activity. Similarly, in cell–attached patches, ouabain also enhanced BK_Ca–channel activity in human RPE (R5) cells. Conclusions: These results indicate that the inhibition of Na⁺,K⁺–ATPase with ouabain could induce cell swelling, thus leading to an increase in BK_Ca–channel activity in these cells. The modification of these channels may influence the function of IPE and RPE cells.

Keywords: ion channels • retinal pigment epithelium