Chelerythrine, a protein kinase C inhibitor, abolishes K flux through Na/K pump and Na‐K‐2Cl cotransporter‐1, and stimulates SK channels in human lens epithelial cells

Abstract

Chelerythrine (CET) is a widely used selective protein kinase C (PKC) inhibitor and proapoptotic agent. Lens cataract formation has been associated with apoptosis and cellular K loss/Na gain. The effect of short‐term CET exposure on both K loss and K uptake, using Rb as congener, was studied in human lens epithelial cells (HLECs) to characterize the role of PKCs in pro‐apoptotic membrane cation transport changes. Ouabain (O), bumetanide (B) and Cl replacement by NO3 were applied to study the Na/K pump, Na‐K‐2Cl cotransporter‐1 (NKCC1), and K‐Cl cotransporter (KCC), respectively, and cations were measured by atomic absorption/emission spectrophotometry. Exposure to 50 μM CET (20 min) inhibited the total, O‐, and OB‐sensitive Rb influxes via Na/K pump and NKCC1 by >90%, with IC50 values of ~ 30 and ~20 μM CET, respectively, without significant KCC activity change. K loss (20–30%) at 20–30 μM CET was 4‐aminopyridine‐insensitive but inhibited by apamin. Since ATP levels did not change, the Na/K pump inhibition may be due to loss of a PKC‐mediated phosphorylation, or direct drug/transporter interaction. Loss of NKCC1 function confirms reported role of PKCδ, present in HLECs, whereas intermediate CET concentrations opens PKC‐regulated SK channels. Apparently, CET affected independently all three transport functions.