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MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Hydroxyl radical activation of a Ca²⁺-sensitive nonselective cation channel involved in epithelial cell necrosis

Instituto de Ciencias Biomédicas and Centro de Estudios Moleculares de la Célula, Facultad de Medicina, Universidad de Chile, Santiago 653-0499, Chile

Submitted 22 January 2004 ; accepted in final form 25 May 2004

In a previous work the involvement of a fenamate-sensitive Ca²⁺-activated nonselective cation channel (NSCC) in free radical-induced rat liver cell necrosis was demonstrated (5). Therefore, we studied the effect of radical oxygen species and oxidizing agents on the gating behavior of a NSCC in a liver-derived epithelial cell line (HTC). Single-channel currents were recorded in HTC cells by the excised inside-out configuration of the patch-clamp technique. In this cell line, we characterize a 19-pS Ca²⁺-activated, ATP- and fenamate-sensitive NSCC nearly equally permeable to monovalent cations. In the presence of Fe²⁺, exposure of the intracellular side of NSCC to H₂O₂ increased their open probability (P_o) by 40% without affecting the unitary conductance. Desferrioxamine as well as the hydroxyl radical (·OH) scavenger MCI-186 inhibited the effect of H₂O₂, indicating that the increase in P_o was mediated by ·OH. Exposure of the patch membrane to the oxidizing agent 5,5'-dithio-bis-2-nitrobenzoic acid (DTNB) had a similar effect to ·OH. The increase in P_o induced by ·OH or DTNB was not reverted by preventing formation or by DTNB washout, respectively. However, the reducing agent dithiothreitol completely reversed the effects on P_o of both ·OH and DTNB. A similar increase in P_o was observed by applying the physiological oxidizing molecule GSSG. Moreover, GSSG-oxidized channels showed enhanced sensitivity to Ca²⁺. The effect of GSSG was fully reversed by GSH. These results suggest an intracellular site(s) of action of oxidizing agents on cysteine targets on the fenamate-sensitive NSCC protein implicated in epithelial cell necrosis.

Ca²⁺-activated channels; radical oxygen species; oxidative stress

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