Retinal voltage-dependent anion channel: characterization and cellular localization.
OBJECTIVE
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 Ca(2+) 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 La(3+) and ruthenium amine binuclear complex (Ru360), which closed the channel. Energized and freshly prepared retinal mitochondria accumulated Ca(2+) that is inhibited by La(3+) ruthenium red and Ru360. Subsequent to Ca(2+) accumulation, mitochondria released the accumulated Ca(2+), probably through activation of the PTP. Ru360 inhibited Ca(2+) 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.
Gincel
Dan
D
Department of Life Sciences and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Vardi
Noga
N
Shoshan-Barmatz
Varda
V
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D005136:Eye Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D018698:Glutamic Acid / Q000494:pharmacology; D006168:Guinea Pigs; D007124:Immunoenzyme Techniques; D017403:In Situ Hybridization; D007473:Ion Channels / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D007811:Lanthanum / Q000494:pharmacology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D018272:Porins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D012160:Retina / Q000378:metabolism*; D017975:Ruthenium Compounds / Q000494:pharmacology; D050995:Voltage-Dependent Anion Channel 1; D050996:Voltage-Dependent Anion Channel 2; D050994:Voltage-Dependent Anion Channels
D005136:Eye Proteins; D007473:Ion Channels; D018272:Porins; D020033:Protein Isoforms; D012333:RNA, Messenger; C112020:Ru 360; D017975:Ruthenium Compounds; C494764:Vdac1 protein, rat; C494767:Vdac2 protein, rat; D050996:Voltage-Dependent Anion Channel 2; D050994:Voltage-Dependent Anion Channels; D018698:Glutamic Acid; D007811:Lanthanum; D050995:Voltage-Dependent Anion Channel 1; D002118:Calcium