The influence of hypotonicity on large-conductance calcium-activated potassium channels in human retinal pigment epithelial cells

The aim of this study was to characterize the effects of hypotonicity on the activity of large-conductance Ca2+-activated K+ (BKCa) channels in human retinal pigment epithelial (RPE R-50) cells. Effects of hypotonicity on ion currents were investigated with the aid of the patch-clamp technique. A regulatory volume decrease in response to a hypotonic solution (200 mOsm/L) was observed that could be blunted by paxilline. In wholecell current recordings, a hypotonic solution (200 mOsm/L) reversibly increased the amplitude of K+ outward currents (IK). The increase of IK could be reversed by iberiotoxin (200 nM), paxilline (1 µM), or tetrandrine (5 µM), but not by glibenclamide (10 µM), disulphonic acid (DIDS) (100 µM), or dequalinium dichloride (10 µM). In RPE R-50 cells pretreated with thapsigargin, aristolochic acid, or pertussis toxin, the increased amplitude of IK in response to hypotonicity was unaltered. In cell-attached patches, an increase in BKCa-channel activity was observed during hypotonicity-indu...