In Saccharomyces cerevisiae, the phosphate carrier is a component of the mitochondrial unselective channel

The mitochondrial permeability transition (PT) involves the opening of a mitochondrial unselective channel (MUC) resulting in membrane depolarization and increased permeability to ions. PT has been observed in many, but not all eukaryotic species. In some species, PT has been linked to cell death, although other functions, such as matrix ion detoxification or regulation of the rate of oxygen consumption have been considered. The identification of the proteins constituting MUC would help understand the biochemistry and physiology of this channel. It has been suggested that the mitochondrial phosphate carrier is a structural component of MUC and we decided to test this in yeast mitochondria. Mersalyl inhibits the phosphate carrier and it has been reported that it also triggers PT. Mersalyl induced opening of the decavanadate-sensitive Yeast Mitochondrial Unselective Channel (YMUC). In isolated yeast mitochondria from a phosphate carrier-null strain the sensitivity to both phosphate and mersalyl was lost, although the permeability transition was still evoked by ATP in a decavanadate-sensitive fashion. Polyethylene glycol (PEG)-induced mitochondrial contraction results indicated that in mitochondria lacking the phosphate carrier the YMUC is smaller: complete contraction for mitochondria from the wild type and the mutant strains was achieved with 1.45 and 1.1 kDa PEGs, respectively. Also, as expected for a smaller channel titration with 1.1 kDa PEG evidenced a higher sensitivity in mitochondria from the mutant strain. The above data suggest that the phosphate carrier is the phosphate sensor in YMUC and contributes to the structure of this channel.