pH difference across the outer mitochondrial membrane measured with a green fluorescent protein mutant

Unique Dimeric Structure of BNip3 Transmembrane Domain Suggests Membrane Permeabilization as a Cell Death Trigger

“…Historically, free permeability of VDAC in all states for small metal cations and protons was assumed, and consequently their concentrations on different sides of the outer membrane were believed to be in equilibrium with TM electric potential difference. Although still debatable, there is growing evidence that permeability of the outer mitochondrial membrane varies in a wider range than used to be recognized and can be very low under some physiological conditions, including stressed states of cells (41,42). Therefore, membrane permeabilization by BNip3 can be of consequence for distribution of ions and electric potential across the outer membrane, which could trigger further events in the cell death scenario.…”

Ratiometric Imaging of pH Probes

“…The mitochondria generate ATP by electron transport across the inner membrane coupled to chemiosmotic H + translocation from the inner membrane space to the matrix through the ATP synthase. The use of dyes to measure the pH of the mitochondrial matrix or inner membrane space in cells is limited by the inability to separate the mitochondria-specific signal from that of the cytoplasmic background (Chacon et al, 1994;Miesenböck et al, 1998;Porcelli et al, 2005). The development of genetically encoded pH-sensitive fluorescent proteins targeted to the mitochondrial matrix and inner membrane space allows determining mitochondrial pH gradients (Boron & De Weer, 1976;De Michele, Carimi, & Frommer, 2014;Pinton et al, 2007); the pH of the mitochondrial matrix is $7.78 while the intermembrane space is $6.88 (Porcelli et al, 2005;Thomas et al, 1979).…”

“…The use of dyes to measure the pH of the mitochondrial matrix or inner membrane space in cells is limited by the inability to separate the mitochondria-specific signal from that of the cytoplasmic background (Chacon et al, 1994;Miesenböck et al, 1998;Porcelli et al, 2005). The development of genetically encoded pH-sensitive fluorescent proteins targeted to the mitochondrial matrix and inner membrane space allows determining mitochondrial pH gradients (Boron & De Weer, 1976;De Michele, Carimi, & Frommer, 2014;Pinton et al, 2007); the pH of the mitochondrial matrix is $7.78 while the intermembrane space is $6.88 (Porcelli et al, 2005;Thomas et al, 1979). Further, spontaneous, transient increases in pHi in the mitochondrial matrix, termed "flashes," have been recently observed and likely reflect changes in proton pump activity and the transmembrane H + gradient (Han & Burgess, 2010;Schwarzländer, Logan, Fricker, & Sweetlove, 2011;Schwarzländer et al, 2012).…”

The crystal structure of mouse VDAC1 at 2.3 Å resolution reveals mechanistic insights into metabolite gating

“…As voltage is increased (Ͼ30 mV) in either a positive or negative direction, a lower conductance, ostensibly the closed state, is obtained. Endogenous potentials caused by chemical gradients across the outer membrane [Donnan potentials (4)] may thus be sufficient to regulate this channel. Although the nature of either of these states is unknown in the absence of structural data, transition between them presumably involves conformational changes constituting a gating action that hinders the passage of metabolites such as adenine nucleotides.…”