Retinal voltage-dependent anion channel: Characterization and cellular localization

PURPOSE. To characterize and localize retinal voltage-dependent anion channel (VDAC) and to understand its possible contribution to mitochondrial function and dysfunction. METHODS. VDAC was characterized by a method involving purification from isolated mitochondria and reconstitution into a planar lipid bilayer (PLB). The permeability transition pore (PTP) was monitored by Ca²⁺ accumulation in isolated mitochondria and swelling of mitochondria. Localization was studied by immunocytochemistry and in situ hybridization. RESULTS. Retinal VDACs exhibited the electrophysiological fingerprint of the VDAC superfamily. It had a maximal chord conductance of 3.7 ± 0.1 nanosiemens (nS) in 1 M NaCl, and a voltage-dependent conductance that was highest at transmembrane potential close to zero. It was modulated by glutamate, which decreased the channel's open probability, and by La³⁺ and ruthenium amine binuclear complex (Ru360), which closed the channel. Energized and freshly prepared retinal mitochondria accumulated Ca²⁺ that is inhibited by La³⁺ ruthenium red and Ru360. Subsequent to Ca²⁺ accumulation, mitochondria released the accumulated Ca²⁺, probably through activation of the PTP. Ru360 inhibited Ca²⁺ release and mitochondrial swelling. VDAC was present in mitochondria of all retinal cell types: photoreceptor, bipolar, horizontal, amacrine, and ganglion cells. Most cells primarily expressed VDAC-1, but they also expressed VDAC-2 and -3. CONCLUSIONS. These results suggest that VDAC is involved in PTP activity and/or regulation and thus is an important player in retinal degeneration associated with PTP-mediated mitochondrial dysfunction.