Combined effect of G3139 and TSPO ligands on Ca2+-induced permeability transition in rat brain mitochondria

• G3139, specific mitochondrial VDAC inhibitor, stimulates mPTP opening in RBM.
• TSPO ligands, 50 μM PK11195 and 1 μM PPIX, accelerate G3139-initiated mPTP.
• G3139 reverses the protective power of 100 nM PK11195 and initiates mPTP opening.
• Anti-TSPO antibodies lose their protective ability in the presence of G3139.
• The lowest Ca2+ capacity was found in the presence of 100 nM PK11195 and G3139.

Permeability of the mitochondrial outer membrane is determined by the activity of voltage-dependent anion channels (VDAC) which are regulated by many factors and proteins. One of the main partner-regulator of VDAC is the 18 kDa translocator protein (TSPO), whose role in the regulation of membrane permeability is not completely understood. We show that TSPO ligands, 1 μM PPIX and PK11195 at concentrations of 50 μM, accelerate opening of permeability transition pores (mPTP) in Ca2+-overloaded rat brain mitochondria (RBM). By contrast, PK11195 at 100 nM and anti-TSPO antibodies suppressed pore opening. Participation of VDAC in these processes was demonstrated by blocking VDAC with G3139, an 18-mer phosphorothioate oligonucleotides, which sensitized mitochondria to Ca2+-induced mPTP opening. Despite the inhibitory effect of 100 nM PK11195 and anti-TSPO antibodies alone, their combination with G3139 considerably stimulated the mPTP opening. Thus, 100 nM PK11195 and anti-TSPO antibody can modify permeability of the VDAC channel and mPTP. When VDAC channels are closed and TSPO is blocked, permeability of the VDAC for calcium seems to be the highest, which leads to accelerated pore opening.