Intracellular localization and isoform expression of the voltage-dependentanion channel (VDAC) in normal and dystrophic skeletal muscle

Voltage-dependent anion channels (VDACs) are a family of pore-forming prote ins encoded by different genes, with at least three protein products expres sed in mammalian tissues. The major recognized functional role of VDACs is to permit the almost free permeability of the outer mitochondrial membrane (OMM). Although VDAC1 is the best known among VDAC isoforms, its exclusivel y mitochondrial location is still debated. Therefore, we have measured its co-localization with markers of cellular organelles or compartments in skel etal muscle fibers by single or double immunofluorescence and traditional a s well as confocal microscopy. Our results show that VDAC1 immunoreactivity corresponds to mitochondria and sarcoplasmic reticulum, while sarcolemmal reactivity, previously reported, was not observed. Since VDAC1 has been sug gested to be involved in the control of oxidative phosphorylation, we sough t for possible gene regulation of VDAC1, VDAC2 and VDAC3 in skeletal muscle of the dystrophin-deficient mdx mouse, which suffers of an impaired contro l of energy metabolism. Our results show that, while VDAC1 mRNA and protein and VDAC2 mRNA are normally expressed, VDAC3 mRNA is markedly down-regulat ed in mdx mouse muscle at different ages (before, during and after the outb urst of myofiber necrosis). This finding suggests a possible involvement of VDAC3 expression in the early pathogenic events of the mdx muscular dystro phy.