K⁺-dependent regulation of matrix volume improves mitochondrial function under conditions mimicking ischemia-reperfusion

Abstract

Korge, Paavo, Henry M. Honda, and James N. Weiss. K ϩ -dependent regulation of matrix volume improves mitochondrial function under conditions mimicking ischemia-reperfusion. To delineate the role of mitochondrial K ϩ fluxes in cardioprotection, we investigated the effect of extramitochondrial K ϩ on the ability of mitochondria to support membrane potential (⌬⌿), regulate matrix volume, consume oxygen, and phosphorylate ADP under conditions mimicking key elements of ischemia-reperfusion. Isolated energized mitochondria responded to ADP addition with depolarization, increased O 2 consumption, and matrix shrinkage. The time required for full recovery of ⌬⌿, signaling the completion of ADP phosphorylation, was used to evaluate the rate of ATP synthesis during repeated ADP pulses. In mitochondria with a decreased ability to support ⌬⌿, the rate of ADP phosphorylation was significantly improved by extramitochondrial K ϩ Ͼ Na ϩ Ͼ Li ϩ , especially at higher buffer osmolarity, which promotes matrix shrinkage. K ϩ -induced improvement in ⌬⌿ recovery after ADP pulses was accompanied by more rapid and complete matrix volume recovery and enhanced O 2 consumption. Manipulations expected to affect matrix swelling by regulating K ϩ fluxes or water distribution indicate that matrix volume regulation by external factors becomes increasingly important in mitochondria with decreased ability to support ⌬⌿ in the face of a high ADP load. Under these conditions, opening of K ϩ influx pathways improved mitochondrial function and delayed failure. This may be an important factor in the mechanism of diaxozide-induced cardioprotection. mitochondria; matrix swelling; shrinkage; hypoxia; reoxygenation ISCHEMIC PRECONDITIONING is known to decrease cardiac injury and improve functional recovery after ischemia-reperfusion by activating a powerful endogenous cardioprotective mechanism. Similar cardioprotection can be induced pharmacologically by putative activators of mitochondrial ATP-sensitive K ϩ (mitoK ATP ) channels. Inoue et al. (18) were the first to demonstrate a mitoK ATP channel in fused giant mitoplasts prepared from liver mitochondria. Subsequently, endogenous mitoK ATP channels were demonstrated using patch-clamp experiments in one additional study (4). These channels were subsequently characterized by Garlid's group (1,13,14,19) in intact mitochondria and, using partially purified protein, reconstituted into liposomes. They found that mitoK ATP channels are much more sensitive to activation by diazoxide and inhibition by 5-hydroxydecanoate (5-HD) than sarcolemmal K ATP channels in the heart (13). Because diazoxide and 5-HD are very effective at inducing and preventing cardioprotection, respectively, the focus turned toward mitoK ATP channels rather than sarcolemmal K ATP channels as mediators of cardioprotection (11,35).Although several hypotheses have been advanced (for reviews, see Refs. 11 and 34), the mechanisms by which mitoK ATP channel openers protect mitochondria from ischemiareperfusion injury remain controversial. At card...

Endogenous and Agonist-induced Opening of Mitochondrial Big Versus Small Ca2+-sensitive K+ Channels on Cardiac Cell and Mitochondrial Protection

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Energetic performance is improved by specific activation of K+ fluxes through KCa channels in heart mitochondria

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Voltage-dependent Inwardly Rectifying Potassium Conductance in the Outer Membrane of Neuronal Mitochondria

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