Gen. Physiol. Biophys. (2006), 25, 325—331 325 Short Communication Tetraphenylphosphonium-Selective Electrode as a Tool for Evaluating Mitochondrial Permeability Transition Pore Function in Isolated Rat Hepatocytes A. Lábajová 1 , J. Kofránek 1 , P. Křiváková 2 , Z. Červinková 2 and Z. Drahota 2,3 1 Institute of Pathophysiology, 1 st Faculty of Medicine, Charles University, Prague, Czech Republic 2 Department of Physiology, Faculty of Medicine, Charles University, Hradec Králové, Czech Republic 3 Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic Abstract. The changes in mitochondrial membrane potential (∆ψ m ) were used as an indicator for evaluating the mitochondrial permeability transition pore (MPTP) function. We found that in situ mitochondria in digitonin-permeabilized hepato- cytes were coupled and responded to the addition of substrates, inhibitors and uncouplers. Ca 2+ -induced ∆ψ m dissipation was caused by MPTP opening because this process was inhibited by cyclosporin A. MPTP opening was enhanced by the pro-oxidant tert-butyl hydroperoxide. Key words: Tetraphenylphosphonium-selective electrode — Mitochondrial per- meability transition pore — Hepatocytes Abbreviations: ∆ψ m , mitochondrial membrane potential; MPTP, mitochondrial permeability transition pore; TPP + , tetraphenylphosphonium; ADP, adenosine diphosphate; t-BHP, tert-butyl hydroperoxide; FCCP, carbonyl cyanide p-trifluoro- methoxyphenylhydrazone; CsA, cyclosporin A; EGTA, ethylene glycol-bis-(β-ami- noethylether) tetraacetic acid. It is now generally accepted that mitochondria are involved in cell apoptosis and that the opening of the mitochondrial permeability transition pore (MPTP) initi- ates the process of cell death (Halestrap et al. 2002; Di Lisa and Bernardi 2006). The participation of the MPTP is involved in both apoptotic and necrotic cell killing and it is associated with hypoxia and ischemia-reperfusion-induced oxidative stress, Correspondence to: Anna Lábajová, Institute of Pathophysiology, 1 st Faculty of Medicine, Charles University, U Nemocnice 5, 120 00 Prague 2, Czech Republic E-mail: Anna.Labajova@lf1.cuni.cz