The high-conductance channel of porin-less yeast mitochondria

Abstract

Patch-clamp and planar bilayer experiments on porin-less yeast mitochondria have allowed the characterization of a cationic channel activated at matrix-side positive (unphysiological) potentials. In voltage-pulse experiments, inactivation was a faster process than activation and the time constant for inactivation was more steeply dependent on voltage than the one for activation. The channel exhibited various conductance states whose occupancy depended on the applied transmembrane potential. In bilayer experiments, the presence of the pCOx-IV leader peptide induced fast gating in a voltage-dependent manner. A comparison with 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 possible relationship of this channel to the mitochondrial megachannel is discussed.

Properties of a Cyclosporin-insensitive Permeability Transition Pore in Yeast Mitochondria

“…The same is true as regards the ion conducting channels in yMt that are observed by patch clamp techniques since the larger examples display conductance values similar to those of the mPTP (15,(21)(22)(23). In addition, ATP favors the open forms although the site is on the matrix side (21,23), and additional regulatory features do not parallel those of the yPTP reported here. The substantial differences in techniques, preparations, and conditions that were used in these studies, and those involving ATP-regulated ion transport, discourage more specific cross-comparisons at present.…”

“…These circumstances complicate the interpretation of earlier studies that reported the absence of an obvious permeability transition in yMt exposed to Ca 2ϩ (20,21). We used the electrophoretic Ca 2ϩ ionophore ETH129 (34,35) to determine if high internal Ca 2ϩ loads trigger a permeability transition in yMt.…”

“…Manon and Guerin (20), investigating electrophoretic pathways of ion transport, reported that Ca 2ϩ is without an effect on the coupling state or swelling and concluded that the existence of a PTP in yMt (yPTP) is uncertain. Szabo et al (21) applied the patch-clamp technique to isolated yMt and observed a channel with multiple conductance levels (100 -600 pS) that is not inhibited by CsA, ADP, or H ϩ . These authors also did not observe Ca 2ϩ related swelling of yMt and were inconclusive regarding the existence of a PTP (21).…”

“…Szabo et al (21) applied the patch-clamp technique to isolated yMt and observed a channel with multiple conductance levels (100 -600 pS) that is not inhibited by CsA, ADP, or H ϩ . These authors also did not observe Ca 2ϩ related swelling of yMt and were inconclusive regarding the existence of a PTP (21). In contrast, Lohret and Kinnally (15,22) described a channel with multiple conductance levels, having a peak conductance of 1-1.5 nS, in patchclamped yeast mitoplasts.…”

The Isolated Complex of the Translocase of the Outer Membrane of Mitochondria

“…A channel with the characteristics of PSC has been previously found in isolated mitochondria of Saccharomyces cerevisiae (43,26,44). We investigated the influence of antibodies directed against the C-terminal 15 residues of yeast Tom40 (␣-yTom40C IgG) on the electrical properties of this channel.…”