HYdrogen peroxide activates k⁺ channels in llc-pk₁ cells

Oxidant-induced damage has been implicated in the pathogenesis of several forms of cellular injury. The activation of K⁺ channels appears to be an early event in injury of renal tubular epithelial cells (Reeves and Shah, J. Clin. Invest. 94: 2289-2294, 1994). The present studies employed patch clamp methods to determine if oxidant stress leads to activation of plasma membrane K+ channels in the renal epithelial LLCPKi cell line. Cellular membrane potential was measured with the perforated whole cell current-clamp recording configuration. Exposure of these cells to H₂U2 (0.1 mM to 5 mM) induced a rapid, dose-dependent membrane hyperpolarization. Whole cell voltage-clamp studies were performed to determine the ion selectivity of the currents underlying this H₂U2-induced cellular hyperpolarization. H₂U2 (5 mM) increased the whole cell current response to a 60 mV depolarizing pulse from 12.3 ± 1.6 pA/pF to 68.3 ±6.6 pA/pF (n = 5). In solutions where EK = -82 mV and ECI = 0 mV, the reversal potential of the H₂U2-induced current was approximately -75 mV, consistent with a K+ selective conductance. This current was inhibited largely (84 ±9%) by barium (5 mM) and glibenclamide (500 |iM), but only partially by tetraethylamonium (15 mM). Single-channel studies revealed two types of Ca-independent, Kselective channels in the H₂02-treated cells: a 40-pS short-open time (5.3 ± 1.2 ms) channel (n =7). and a 20-pS long-open time (60 ±8 ms) channel (n =5). These findings indicate that H₂₂ activates a Caindependent K⁺ conductance in LLC-PKi cells. This activation may have a role in the pathogenesis of oxidant-induced cell injury. Supported by the American Heart Association.