Voltage-dependent anion channel localises to the plasma membrane and peripheral but not perinuclear mitochondria

Activity of the antioestrogen-activated maxi-Cl(-) channel has been recorded in different cell types, including fibroblasts, vascular smooth muscle, endothelial and neuroblastoma cells. Its electrophysiological properties resemble those of the voltage-dependent anion channel (VDAC) of the outer mitochondrial membrane, a channel of particular relevance to the physiology and pathophysiology of mitochondria. The hypothesis that VDAC could be the molecular correlate of the plasma membrane maxi-Cl(-) channel has been debated over the last few years, with the lack of clear evidence for the presence of VDAC in the plasma membrane constituting the main argument of the detractors. In the present study, we investigated the cellular localisation of VDAC in NIH3T3 fibroblasts. The presence of a plasma membrane VDAC was demonstrated by immunoblotting of membrane fractions with monoclonal antibodies against the VDAC and by RT-PCR using primers that hybridise to a VDAC sequence coding for a N-terminal leader peptide required for its plasma membrane sorting. In addition, confocal microscopy studies showed the colocalisation of VDAC with caveolin-1. As expected, VDAC also localised to mitochondria. Colocalisation studies with TOM-20, a protein also present in the outer mitochondrial membrane, showed that VDAC proteins localised only to peripheral and not to perinuclear mitochondria.