Mitochondrial depolarization underlies delay in permeability transition by preconditioning with isoflurane: roles of ROS and Ca2+

Abstract

During reperfusion, the interplay between excess reactive oxygen species (ROS) production, mitochondrial Ca2+ overload, and mitochondrial permeability transition pore (mPTP) opening, as the crucial mechanism of cardiomyocyte injury, remains intriguing. Here, we investigated whether an induction of a partial decrease in mitochondrial membrane potential (ΔΨm) is an underlying mechanism of protection by anesthetic-induced preconditioning (APC) with isoflurane, specifically addressing the interplay between ROS, Ca2+, and mPTP opening. The magnitude of APC-induced decrease in ΔΨm was mimicked with the protonophore 2,4-dinitrophenol (DNP), and the addition of pyruvate was used to reverse APC- and DNP-induced decrease in ΔΨm. In cardiomyocytes, ΔΨm, ROS, mPTP opening, and cytosolic and mitochondrial Ca2+ were measured using confocal microscope, and cardiomyocyte survival was assessed by Trypan blue exclusion. In isolated cardiac mitochondria, antimycin A-induced ROS production and Ca2+ uptake were determined spectrofluorometrically. In cells exposed to oxidative stress, APC and DNP increased cell survival, delayed mPTP opening, and attenuated ROS production, which was reversed by mitochondrial repolarization with pyruvate. In isolated mitochondria, depolarization by APC and DNP attenuated ROS production, but not Ca2+ uptake. However, in stressed cardiomyocytes, a similar decrease in ΔΨm attenuated both cytosolic and mitochondrial Ca2+ accumulation. In conclusion, a partial decrease in ΔΨm underlies cardioprotective effects of APC by attenuating excess ROS production, resulting in a delay in mPTP opening and an increase in cell survival. Such decrease in ΔΨm primarily attenuates mitochondrial ROS production, with consequential decrease in mitochondrial Ca2+ uptake.