THE HIGH-CONDUCTANCE CHANNEL OF PORIN-LESS YEAST MITOCHONDRIA

Patch-clamp and planar bilayer experiments on porin-less yeast mitocho ndria have allowed the characterization of a cationic channel activate d at matrix-side positive (unphysiological) potentials. In voltage-pul se experiments, inactivation was a faster process than activation and the time constant for inactivation was more steeply dependent on volta ge than the one for activation. The channel exhibited various conducta nce states whose occupancy depended on the applied transmembrane poten tial. In bilayer experiments, the presence of the pCOx-IV leader pepti de induced fast gating in a voltage-dependent manner. A comparison wit h previously described activities suggests that the pore may coincide with the peptide-sensitive channel (PSC) (Thieffry et al. (1988) EMBO J. 7, 1449-1454) as well as with two other activities (Dihanich et al. (1989) Eur. J. Biochem. 181, 703-708; Tedeschi et al. (1987) J. Membr . Biol. 97, 21-29) assigned to the mitochondrial outer membrane. The p ossible relationship of this channel to the mitochondrial megachannel is discussed.