Abstract Electrophysiological records suggest that the pore responsible for the mitochondrial Ca 2+-dependent permeability transition (FTP), identified as the mitochondrial megachannel (MMC) observed in patch-clamp experiments, may comprise two cooperating porin (VDAC) molecules. We have re-investigated the voltage dependence of the megachannel, which favors the closed state(s) at negative (physiological) transmembrane potentials. This behavior confirms that MMC corresponds to the permeabilization pore. As detailed in the accompanying paper [(1993) FEBS Lett. 330, 206-210] this voltage dependence resembles that of VDAC. Alpidem, a ligand of the mitochondrial benzodiazepine receptor, which reportedly comprises VDAC, the adenine nucleotide carrier and a third component, elicited currents from silent mitoplast patches, suggesting that the benzodiazepine receptor may be identical to the PTP/MMC.