Reversal of impaired oxidative phosphorylation and calcium overloading in the skeletal muscle mitochondria of CHF-146 dystrophic hamsters.

Abstract

Membrane-mediated excessive intracellular calcium accumulation (EICA) and diminished cellular energy production are the hallmarks of dystrophic pathobiology in Duchenne and Becker muscular dystrophies. We reported reversal of respiratory damage and Ca(2+)-overloading in the in vitro cardiac mitochondria from CHF-146 dystrophic hamsters (DH) with hereditary muscular dystrophy (Bhattacharya et al., 1993). Here we studied respiratory dysfunctions in the skeletal muscle mitochondria from young and old DH, and whether these abnormalities can be reversed by reducing [Ca2+] in the isolation medium, thereby lowering intramitochondrial Ca(2+)-overloading. Age- and sex-matched CHF-148 albino normal hamsters (NH) served as controls. As an index of EICA and cellular degeneration, Ca and Mg levels were assayed in the skeletal muscle and mitochondria. Mitochondria from young and old DH, isolated without EDTA (BE medium), revealed poor coupling of oxidative phosphorylation, diminished stimulated oxygen consumption rate, and lower respiratory control ratio and ADP/O ratios, compared to NH. Incorporation of 10 mM EDTA (Bo medium) in the isolation medium restored mitochondrial functions of the dystrophic organelles to a near-normal level, and reduced Ca(2+)-overloading. The mitochondrial Ca level in DH was significantly higher than in NH, irrespective of the medium. However, compared to Bo medium, the dystrophic organelles isolated in BE medium had lower Ca levels and markedly improved oxidative phosphorylation as seen in NH. Muscle Ca contents in the young and old DH were elevated relative to NH, showing a positive correlation with the increased mitochondrial Ca(2+)-sequestration. Dystrophic muscle also revealed Ca deposition with an abundance of Ca(2+)-positive and necrotic myofibers by light microscopy, and intramitochondrial Ca(2+)-overloading by electron microscopy, respectively. However, Mg levels in the muscle and mitochondria did not alter with age or dystrophy. These data parallel our observations in the heart, and suggest that functional impairments and Ca(2+)-overloading also occur in the skeletal muscle mitochondria of DH, and are indeed reversible if EICA is regulated by slow Ca(2+)-channel blocker therapy (Johnson and Bhattacharya, 1993).