Bax increases the pore size of rat brain mitochondrial voltage-dependent anion channel in the presence of tBid Jyotirmoy Banerjee, Subhendu Ghosh * Department of Biophysics, University of Delhi South Campus, New Delhi 110021, India Received 29 July 2004 Abstract Voltage-dependent anion channel (VDAC), Bax, and tBid play a central role in apoptosis regulation but their functioning is still very controversial. VDAC forms voltage gated pore in planar lipid bilayers, and acts as the pathway for the movement of substances in and out of the mitochondria by passive diffusion. Here we report that there is increase in the pore size of VDAC in the presence of Bax and tBid through bilayer electrophysiological experiments. We hereby hypothesize that this increase in pore size might cause swelling in the mitochondria, leading to the rupture of mitochondrial outer membrane and release of cytochrome c causing brain cell death. Ó 2004 Elsevier Inc. All rights reserved. Keywords: Brain VDAC; Bax; tBid; BLM; Electrophysiology; Apoptosis Apoptosis is critical for normal nervous system devel- opment and is tightly regulated by an evolutionary con- served molecular program [1]. It is also essential for tissue homeostasis and elimination of harmful animals in metazoan animals [2,3]. There are several hypotheses regarding the mechanism of apoptosis. Some of these say that, voltage-dependent anion channel (VDAC) is involved in apoptosis. VDAC is an abundant protein in the outer mitochondrial membrane, which forms large voltage gated pore (2.5–3 nm) in planar lipid bilay- ers, and acts as the pathway for the movement of sub- stances in and out of the mitochondria by passive diffusion [4]. There are many reports, which say that Bax and Bid proteins are the key molecules involved in cell death. Bax and Bid are the members of the Bcl- 2 family of proteins, which are well-characterized regu- lators of apoptosis [5,6]. One of the models proposes that the Bax interacts with VDAC resulting in cytochrome c permeation through the outer mitochondrial membrane [7,8]. Cyto- chrome c, which normally resides exclusively in the intermembrane space of mitochondria, is released into cytosol during apoptosis [9]. Release of cytochrome c from mitochondria inactivates the electron transfer chain and triggers caspase activation through Apaf 1 [10,11]. Caspases, a group of cysteine proteases that cleave protein substrates after the aspartic acid residues, play a central role in regulation and execution of apop- tosis [12]. Caspases that function in the apoptotic path- way exist as inactive zymogens in the cytosol of living cells and become activated through proteolysis when cells receive apoptotic signals. Another model proposes that closure of VDAC chan- nel prevents the efficient exchange of ATP and ADP be- tween the cytosol and mitochondrial matrix [13]. Loss of the outer membrane permeability due to VDAC clo- sure might result in the accumulation of the products of mitochondrial activity within the intermembrane space, generation of an osmotic gradient, and matrix swelling followed by the rupture of the outer membrane. The anti-apoptotic protein Bcl-x L restores the ATP/ADP ex- change by promoting the open configuration of the VDAC channel, shown in planar bilayer experiments [14]. 0006-291X/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2004.08.094 * Corresponding author. Fax: +91 11 26885270. E-mail address: subhog@vsnl.com (S. Ghosh). www.elsevier.com/locate/ybbrc Biochemical and Biophysical Research Communications 323 (2004) 310–314 BBRC