Abstract

Volume-sensitive outwardly rectifying (VSOR) Cl- channels participate in several physiological processes such as regulatory volume decrease, cell cycle regulation, proliferation and apoptosis. Recent evidence points to a significant role of hydrogen peroxide (H2O2) in VSOR Cl- channel activation. The aim of this study was to determine the signalling pathways responsible for H2O 2-induced VSOR Cl- channel activation. In rat hepatoma (HTC) cells, H2O2 elicited a transient increase in tyrosine phosphorylation of phospholipase Cγ1 (PLCγ1) that was blocked by PP2, a Src-family protein kinases inhibitor. Also, H 2O2 triggered an increase in cytosolic [Ca2+] that paralleled the time course of PLCγ1 phosphorylation. The H 2O2-induced [Ca2+]i rise was prevented by the generic phospholipase C (PLC) inhibitor U73122 and the inositol 1,4,5-trisphosphate-receptor (IP3R) blocker 2-APB. In line with these results, manoeuvres that prevented PLCγ1 activation and/or [Ca 2+]i rise, abolished H2O2-induced VSOR Cl- currents. Furthermore, in cells that overexpress a phosphorylation-defective dominant mutant of PLCγ1, H2O 2 did not induce activation of VSOR Cl- currents. All these H2O2-induced effects were independent of extracellular Ca2+. Our findings suggest that activation of PLCγ1 and subsequent Ca2+ i mobilisation mediate H2O2-induced VSOR Cl- currents, indicating that H2O2 operates via redox-sensitive signalling pathways akin to those activated by osmotic challenges. Copyright © 2007 S. Karger AG.