Cytosolic Ca²⁺ and protein kinase Cα couple cellular metabolism to membrane K⁺ permeability in a human biliary cell line

Cholangiocytes represent an important target of injury during the ischemia and metabolic stress that accompanies liver preservation. Since K⁺ efflux serves to minimize injury during ATP depletion in certain other cell types, the purpose of these studies was to evaluate the effects of ATP depletion on plasma membrane K⁺ permeability of Mz-ChA-1 cells, a model human biliary cell line. Cells were exposed to dinitrophenol (50 μM) and 2- deoxyglucose (10 mM) as the standard model of metabolic injury. Whole-cell and single K⁺ channel currents were measured using patch clamp techniques; and intracellular [Ca²⁺] ([Ca²⁺](i)) was estimated by calcium green-1 fluorescence. Metabolic stress increased [Ca²⁺](i), and stimulated translocation of the α isoform of protein kinase C (PKCα) from cytosolic to particulate cell fractions. The same maneuver increased membrane K⁺ permeability 40-70-fold as detected by (a) activation of K⁺-selective whole cell currents of 2,176±218 pA (n = 34), and (b) opening of apamin-sensitive K⁺ channels with a unitary conductance of 17.0±0.2 pS. PKCα translocation and channel opening appear to be related since stress-induced K⁺ efflux is inhibited by chelation of cytosolic Ca²⁺, exposure to the PKC inhibitor chelerythrine (25 μM) and downregulation of PKC by phorbol esters. Moreover, K⁺ currents were activated by intracellular perfusion with recombinant PKCα in the absence of metabolic inhibitors. These findings indicate that in biliary cells apamin-sensitive K⁺ channels are functionally coupled to cell metabolism and suggest that cytosolic Ca²⁺ and PKCα are selectively involved in the response.