AN ELECTROPHYSIOLOGICAL STUDY OF YEAST MITOCHONDRIA - EVIDENCE FOR 2 INNER MEMBRANE ANION CHANNELS SENSITIVE TO ATP

The inner membrane of mitochondria from various strains of Saccharomyc es cerevisiae has been analyzed with the patch clamp technique for com parison with the better known homologous membrane in mammals (Sorgato, M. C., and Moran, O. (1993) CRC Grit. Rev. Biochem. Mol. Biol. 18, 12 7-171). Differently than in mammals, the yeast inner membrane was foun d to harbor essentially two channels with similar anionic selectivity but otherwise different functional behavior. One had a conductance of around 45 picosiemens (in symmetrical 150 mM KCl) and an activity only marginally sensitive to voltage. The other channel was prominent for the higher outwardly rectifying current and for the dependence upon vo ltage of the open probability that induced rapid closure at physiologi cal (negative) membrane potentials. Particularly interesting was the e ffect of ATP (Mg2+ free) added on the matrix side of the membrane, In the case of the lower conducting channel, the nucleotide caused an imm ediate block of activity (IC50, 0.240 mM), whereas it locked the large r conductance in the open state at both positive and negative potentia ls, In proteoliposomes containing both mitochondrial membranes, the sm all conductance was clearly evident, whereas a larger channel, cationi c and without the voltage dependence typical of that in the native inn er membrane, was found.