Blockade of Electron Transport during Ischemia Protects Cardiac Mitochondria

Abstract

Subsarcolemmal mitochondria sustain progressive damage during myocardial ischemia. Ischemia decreases the content of the mitochondrial phospholipid cardiolipin accompanied by a decrease in cytochrome c content and a diminished rate of oxidation through cytochrome oxidase. We propose that during ischemia mitochondria produce reactive oxygen species at sites in the electron transport chain proximal to cytochrome oxidase that contribute to the ischemic damage. Isolated, perfused rabbit hearts were treated with rotenone, an irreversible inhibitor of complex I in the proximal electron transport chain, immediately before ischemia. Rotenone pretreatment preserved the contents of cardiolipin and cytochrome c measured after 45 min of ischemia. The rate of oxidation through cytochrome oxidase also was improved in rotenone-treated hearts. Inhibition of the electron transport chain during ischemia lessens damage to mitochondria. Rotenone treatment of isolated subsarcolemmal mitochondria decreased the production of reactive oxygen species during the oxidation of complex I substrates. Thus, the limitation of electron flow during ischemia preserves cardiolipin content, cytochrome c content, and the rate of oxidation through cytochrome oxidase. The mitochondrial electron transport chain contributes to ischemic mitochondrial damage that in turn augments myocyte injury during subsequent reperfusion.

Cardiac H11 kinase/Hsp22 stimulates oxidative phosphorylation and modulates mitochondrial reactive oxygen species production: Involvement of a nitric oxide-dependent mechanism

“…Indeed, anoxia strongly reduces mitochondrial respiration from TG mice, an effect which is sensitive to L-NAME treatment, and this leads to a strong inhibition of post-anoxia ROS generation. It should be noted that this inhibition of mitochondrial functions in TG mice during anoxia is similar to that described for nitrite, which also exhibits cardioprotective properties [25] and that pharmacological inhibition of mitochondrial respiration during ischemia was shown to improve post-ischemic reperfusion 15 injury [40,41]. Thus, mitochondria from TG mice appear naturally protected against ischemic stress and react like mitochondria from WT mice subjected to a protective pharmacological treatment.…”

Protein kinase Cϵ interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

“…Therefore differences in the mechanisms of PC in neonatal versus adult myocardium may exist. We would also like to point out that these studies [55][56][57][58] did not confirm the involvement of the PKCε isoenzyme in PC, opening the possibility that they may have been studying an altogether different cardioprotective mechanism(s) than we did. In addition, it is not clear that inhibition of ETC function is the direct cause of protection.…”

“…It is likely that 45 min of ischaemia would by itself inhibit complex IV substantially and therefore the proposed protective mechanism of KCN would be related to its continuous inhibition of complex IV during reperfusion. This method is very different from the one we used, and it is entirely possible that both methods (ours and those of [55][56][57][58]) could induce protection, particularly in light of the fact that, in recent studies, cardiac post-conditioning (i.e. pharmacological treatments or brief periods of reperfusion and ischaemia prior to a prolonged reperfusion) in cardiac myocytes has been shown to produce equal protection as the PC methods [60].…”

“…In the studies by Lesnefsky et al [57], 60 µM concentration of the irreversible ETC complex I inhibitor rotenone administered to ex vivo rat hearts prior to prolonged ischaemia (without washout or reperfusion) prevented ROS production and inhibition of complex IV activity. It is very possible that different signalling mechanisms could be induced by their experimental conditions from those evoked in our NCM model of hypoxic PC, particularly since their study involved continuous incubation with rotenone throughout the index ischaemia period.…”

“…For example, Ganote et al reported potassium cyanide (KCN) [55] and DNP (2,4-dinitrophenol) [56]-induced cardiac protection against ischaemia/reperfusion injury in ex vivo adult rat hearts. Lesnefsky et al [57] found that perfusion of adult rat hearts with the complex I inhibitor rotenone for 1 min prior to and during 45 min of ischaemia induced cardiac PC. Additionally, Holmuhamedov et al [58] reported that the mK ATP (mitochondrial ATP-dependent potassium) channel-opening drugs diazoxide and pinacidil had protonophoric effects on adult rat hearts to uncouple mitochondrial membrane potential as a mechanism of PC.…”