Activation of potassium and chloride channels by tumor necrosis factor α: Role in liver cell death

Abstract

Despite abundant evidence for changes in mitochondrial membrane permeability in tumor necrosis factor (TNF)-mediated cell death, the role of plasma membrane ion channels in this process remains unclear. These studies examine the influence of TNF on ion channel opening and death in a model rat liver cell line (HTC). TNF (25 ng/ml) elicited a 2- and 5-fold increase in K+ and Cl- currents, respectively, in HTC cells. These increases occurred within 5-10 min after TNF exposure and were inhibited either by K+ or Cl- substitution or by K+ channel blockers (Ba2+, quinine, 0.1 nM each) or Cl- channel blockers (10 μM 5-nitro-2-(3-phenylpropylamino)benzoic acid and 0.1 nM N-phenylanthranilic acid), respectively. TNF-mediated increases in K+ and Cl- currents were each inhibited by intracellular Ca2+ chelation (5 nM EGTA), ATP depletion (4 units/ml apyrase), and the protein kinase C (PKC) inhibitors chelerythrine (10 μM) or PKC 19-36 peptide (1 μM). In contrast, currents were not attenuated by the calmodulin kinase II 281-309 peptide (10 μM), an inhibitor of calmodulin kinase II. In the presence of actinomycin D (1 μM), each of the above ion channel blockers significantly delayed the progression to TNF-mediated cell death. Collectively, these data suggest that activation of K+ and Cl- channels is an early response to TNF signaling and that channel opening is Ca2+- and PKC-dependent. Our findings further suggest that K+ and Cl- channels participate in pathways leading to TNF- mediated cell death and thus represent potential therapeutic targets to attenuate liver injury from TNF.