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 (H 2 O 2 ) in VSOR Cl - channel activation. The aim of this study was to determine the signalling pathways responsible for H 2 O 2 -induced VSOR Cl - channel activation. In rat hepatoma (HTC) cells, H 2 O 2 elicited a transient increase in tyrosine phosphorylation of phospholipase Cγ1 (PLCγ1) that was blocked by PP2, a Src-family protein kinases inhibitor. Also, H 2 O 2 triggered an increase in cytosolic [Ca 2+ ] that paralleled the time course of PLCγ1 phosphorylation. The H 2 O 2 -induced [Ca 2+ ] i rise was prevented by the generic phospholipase C (PLC) inhibitor U73122 and the inositol 1,4,5-trisphosphate-receptor (IP 3 R) blocker 2-APB. In line with these results, manoeuvres that prevented PLCγ1 activation and/or [Ca 2+ ] i rise, abolished H 2 O 2 -induced VSOR Cl - currents. Furthermore, in cells that overexpress a phosphorylation-defective dominant mutant of PLCγ1, H 2 O 2 did not induce activation of VSOR Cl - currents. All these H 2 O 2 -induced effects were independent of extracellular Ca 2+ . Our findings suggest that activation of PLCγ1 and subsequent Ca 2+ i mobilisation mediate H 2 O 2 -induced VSOR Cl - currents, indicating that H 2 O 2 operates via redox-sensitive signalling pathways akin to those activated by osmotic challenges.
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