Functional Distinctions between the Mitochondrial ATP-dependent K+ Channel (mitoKATP) and Its Inward Rectifier Subunit (mitoKIR)

Abstract

The ATP-sensitive potassium channel from the inner mitochondrial membrane (mitoK ATP ) is a highly selective conductor of K ؉ ions. When isolated in the presence of nonionic detergent and reconstituted in liposomes, mitoK ATP is inhibited with high affinity by ATP (K 1/2 ‫؍‬ 20 -30 M). We have suggested that holo-mitoK ATP is a heteromultimer consisting of an inwardly rectifying K The importance of the mitochondrial K ϩ cycle for volume regulation, reviewed by Garlid and Paucek (1) was recognized by Mitchell (2) long before any of the components of this cycle were discovered. K ϩ is driven into the matrix by the high membrane potential (⌬⌿) 1 generated by the proton-pumping electron transport system, and excess K ϩ is removed by the regulated K ϩ /H ϩ antiporter. Electrophoretic K ϩ influx occurs by diffusion and by means of ATP-sensitive potassium channel from the inner mitochondrial membrane (mitoK ATP ). At the high values of ⌬⌿ maintained by mitochondria, both of these processes increase exponentially with ⌬⌿ (3, 4) and are consequently very sensitive to fluctuations in ⌬⌿. These fluctuations, in turn, are high in tissues such as heart, which undergo large variations in energy demand and ATP synthesis rates (5). Thus, regulation of K ϩ influx and efflux pathways can be seen as a means of regulating volume in the face of the changing energy requirements of the cell. MitoK ATP plays more than a housekeeping role in cell physiology. There is now general agreement that mitoK ATP plays a key role in cardioprotection against ischemia-reperfusion injury (6, 7). The proposed mechanisms of this protective effect of mitoK ATP opening (5, 8, 9) are plausible; however, it is evident that more needs to be known about the functional properties of mitoK ATP before its role in vivo can be ascertained.By using a novel ethanol extraction technique, Mironova et al. (10) were the first to report reconstitution in lipid bilayer membranes of a 55-kDa K ϩ channel from mitochondria. Paucek et al. (3) used a detergent extraction technique and were the first to report reconstitution of mitoK ATP in liposomes. The latter channel was associated with two proteins of molecular mass 55 and 63 kDa, and we hypothesized that mitoK ATP is a heteromultimeric complex consisting of a 55-kDa inwardly rectifying K ϩ channel (mitoKIR) and a 63-kDa sulfonylurea receptor (mitoSUR), analogous to the plasma membrane ATPdependent K ϩ channel (cellK ATP ) (11,12). In this report, we focus on three interactions that address the key question of whether the 55-kDa K ϩ channel protein observed in the ethanol purification is the same as the 55-kDa protein purified with detergents. First, we show that UDP reverses ATP-inhibition of K ϩ flux mediated by both mitoKIR and mitoK ATP reconstituted in liposomes. Moreover, UDP exerts the same action in isolated mitochondria, and the affinities for the opening effect of UDP are about the same in each preparation. Second, we show that the mitoKIR opener p-diethylaminoethylbenzoate (DEB) also activates K ϩ flux via ...

A Biophysical Model of the Mitochondrial Respiratory System and Oxidative Phosphorylation

“…Sensitivity analysis reveals that the activities of the channels cannot be determined based on the present dataset. The activities of potassium channels are known to be modulated by ischemic and anesthetic preconditioning [31,36,37] and will be explored in future work. The fits obtained using equation 24 to model the complex III flux are plotted in Figures 4 and 5.…”

“…Mitochondrial ATP-dependent potassium channel flux [17,18,37,[44][45][46][47] will need to be incorporated to investigate the cardiac metabolic response to ischemia, hypoxia, and preconditioning. In addition, kinetic data must be obtained to effectively parameterize and validate the timedependent behavior of the model.…”

F 1 F O-ATPase Activity and ATP Dependence of Mitochondrial Energization in Proximal Tubules after Hypoxia/Reoxygenation

“…Large fractions of the added ADP and AMP were converted to ATP, so it can account for their effects. In view of these actions of ATP to prevent spontaneous de-energization, we tested whether this de-energization was mediated by mitochondrial ATP-sensitive K ϩ channels using channel inhibitors (18). Neither glibenclamide nor 5-hydroxydecanoate reproduced the effect of ATP to prevent the mitochondrial de-energization.…”

The use of gliclazide in the mirror of the individualized sulfonylurea therapy

“…Szerepük lehet az oxidatív stresszel szembeni védekezésben, a sejtműködés szabályozásában, a mitochondrialis membrán permeabilitásának szabályozásában. Egyes megfi gyelések szerint mind SUR-aktivátorok (például glibenclamid), mind gátlók (például diazoxid) befolyásolják működését [14,15].…”