Disease-Related Modification of Chloride Conductance in Skeletal Muscle of Dystrophic Mice: Expression of CLC-1 Channel and Role of Inflammation and Oxidative Stress-Related Signaling

Abstract

A decrease in resting chloride channel conductance (gCl) occurs in dystrophin-deficient myofibers of mdx mouse as a consequence of both spontaneous degeneration, as in diaphragm (DIA), or exercise-induced damage as in fast-twitch EDL muscle (De Luca et al., J. Pharmacol. Exp. Ther. 2003). Alterations in gCl, in parallel with markers of inflammation, can be contrasted by small restoration in dystrophin expression (De Luca et al., Neurobiol Dis, 2008). We focused on the molecular mechanisms underlying gCl impairment and its relation to primary defect. Preliminary qRT-PCR experiments showed a 30-35% reduction of CLC-1 mRNA in both DIA and EDL muscles of mdx mice, irrespective to exercise regimen. The reduction was consistent with the impairment of gCl detected in concomitant electrophysiological experiments in DIA and EDL myofibers; however the selective alteration of gCl in exercised mdx EDL muscle remained unexplained. Further experiments are ongoing to evaluate the possible outcome of pathology and mechanical stress on CLC-1 channel protein level and on the expression of other chloride channel types. Recent results showed that in vivo inhibition of angiotensin (Ang)-II contrasts the decrease in gCl in mdx EDL muscle, disclosing a possible role of this pro-inflammatory and pro-oxidative mediator in chloride channel function (Cozzoli et al., Pharmacol Res 2011). The application of Ang-II to wt EDL fibers reduced gCl in a concentration-dependent manner, with a half-maximal concentration of 67nM. The effect was inhibited by the AT1-receptor antagonist losartan, as well as by the PKC-inhibitor chelerythrine, the antioxidant N-acetyl-cysteine and the inhibitor of NADPH-oxidase apocynin. The results demonstrate that CLC-1 channel expression is affected in dystrophinopathies and that further modulation of gCl is related to inflammation and oxidative stress in skeletal muscle.