Modulation of the voltage-dependent anion channel (VDAC) by glutamate.
The voltage-dependent anion channel (VDAC), also known as mitochondrial porin, is a large channel permeable to anions, cations, ATP, and other metabolites. VDAC was purified from sheep brain synaptosomes or rat liver mitochondria using a reactive red-agarose column, in addition to the hydroxyapatitate column. The red-agarose column allowed further purification (over 98%), concentration of the protein over ten-fold, decreasing Triton X-100 concentration, and/or replacing Triton X-100 with other detergents, such as Nonidet P-40 or octylglucoside. This purified VDAC reconstituted into planar-lipid bilayer, had a unitary maximal conductance of 3.7 +/- 0.1 nS in 1 M NaCl, at 10 mV and was permeable to both large cations and anions. In the maximal conducting state, the permeability ratios for Na(+), acetylcholine(+), dopamine,(+) and glutamate(-), relative to Cl(-), were estimated to be 0.73, 0.6, 0.44, and 0.4, respectively. In contrast, in the subconducting state, glutamate(-) was impermeable, while the relative permeability to acetylcholine(+) increased and to dopamine(+) remained unchanged. At the high concentrations (0.1-0.5 M) used in the permeability experiments, glutamate eliminated the bell shape of the voltage dependence of VDAC channel conductance. Glutamate at concentrations of 1 to 20 mM, in the presence of 1 M NaCl, was found to modulate the VDAC channel activity. In single-channel experiments, at low voltages (+/-10 mV), glutamate induced rapid fluctuations of the channel between the fully open state and long-lived low-conducting states or short-lived closed state. Glutamate modification of the channel activity, at low voltages, is dependent on voltage, requiring short-time (20-60 sec) exposure of the channel to high membrane potentials. The effect of glutamate is specific, since it was observed in the presence of 1 M NaCl and it was not obtained with aspartate or GABA. These results suggest that VDAC possesses a specific glutamate-binding site that modulates its activity.
Gincel
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D
Department of Life Sciences, The Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
Silberberg
S D
SD
Shoshan-Barmatz
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V
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D053078:Membrane Potential, Mitochondrial; D008930:Mitochondria, Liver / Q000378:metabolism; D051381:Rats; D012756:Sheep; D012964:Sodium / Q000378:metabolism; D055366:Synaptic Potentials; D013574:Synaptosomes / Q000378:metabolism; D050994:Voltage-Dependent Anion Channels / Q000187:drug effects* / Q000378:metabolism*
D002712:Chlorides; D050994:Voltage-Dependent Anion Channels; D018698:Glutamic Acid; D012964:Sodium; D000109:Acetylcholine; D004298:Dopamine