Nonselective cation channels as effectors of free radical-induced rat liver cell necrosis

Abstract

Necrosis, as opposed to apoptosis, is recognized as a nonspecific cell death that induces tissue inflammation and is preceded by cell edema. In non-neuronal cells, the latter has been explained by defective outward pumping of Na(+) caused by metabolic depletion or by increased Na(+) influx via membrane transporters. Here we describe a novel mechanism of swelling and necrosis; namely the influx of Na(+) through oxidative stress-activated nonselective cation channels. Exposure of liver epithelial Clone 9 cells to the free-radical donors calphostin C or menadione induced the rapid activation of an approximately 16-pS nonselective cation channel (NSCC). Blockage of this conductance with flufenamic acid protected the cells against swelling, calcium overload, and necrosis. Protection was also achieved by Gd(3+), an inhibitor of stretch-activated cation channels, or by isosmotic replacement of extracellular Na(+) with N-methyl-D-glucamine. It is proposed that NSCCs, which are ubiquitous although largely inactive in healthy cells, become activated under severe oxidative stress. The ensuing influx of Na(+) initiates a positive feedback of metabolic and electrolytic disturbances leading cells to their necrotic demise.