An electrophysiological study of yeast mitochondria. Evidence for two inner membrane anion channels sensitive to ATP

The inner membrane of mitochondria from various strains of Saccharomyces cerevisiae has been analyzed with the patch clamp technique for comparison with the better known homologous membrane in mammals (Sorgato, M. C., and Moran, O. (1993) CRC Crit. Rev. Biochem. Mol. Biol. 18, 127-171). Differently than in mammals, the yeast inner membrane was found 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 voltage of the open probability that induced rapid closure at physiological (negative) membrane potentials. Particularly interesting was the effect of ATP (Mg2+ free) added on the matrix side of the membrane. In the case of the lower conducting channel, the nucleotide caused an immediate block of activity (IC50, 0.240 mM), whereas it locked the larger conductance in the open state at both positive and negative potentials. In proteoliposomes containing both mitochondrial membranes, the small conductance was clearly evident, whereas a larger channel, cationic and without the voltage dependence typical of that in the native inner membrane, was found.