Ca2+ and ETH-129 don't cause swelling or a large ΔΨ drop when mitochondria are suspended in KCl. panel A, the medium contained 0.3 M KCl, 10 mM HEPES, pH 7.20, 10 mM KPi, and 0.5 mg/ml BSA. 1 mM ethanol, 80 μM CaCl2, and 3.6 μM ETH-129 were present as shown. panel B, the medium contained a 0.6 osM mixture of 0.3 M KCl and 0.6 M mannitol, 10 mM HEPES (TEA+), pH 7.20, 10 mM KPi, 0.5 mg/ml BSA, and 12 μM safranine O. 1 mM ethanol, 80 μM CaCl2, 3.6 μM ETH-129, and 4 μM FCCP were added where indicated. 1 mM ethanol was chosen because this concentration prevents mitochondrial swelling in a 0.3 M KCl medium.