Preconditioning limits mitochondrial Ca²⁺during ischemia in rat hearts: role of K_ATPchannels

Abstract

Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca(2+)]i), which is thought to play a critical role in ischemia-reperfusion injury. Ischemic preconditioning (PC) improves myocardial function during ischemia-reperfusion, a process that may involve opening mitochondrial ATP-sensitive potassium (K(ATP)) channels. Because pharmacological limitation of mitochondrial calcium concentration ([Ca(2+)]m) overload during ischemia-reperfusion has been shown to improve myocardial function, we hypothesized that PC would reduce [Ca(2+)]m during ischemia-reperfusion and that this effect was mediated by opening mitochondrial K(ATP) channels. Isolated rat hearts were subjected to 25 min of global ischemia and 30 min of reperfusion with or without PC in the presence of mitochondrial K(ATP) channel opening (diazoxide, 100 microM) and blockade [5-hydroxydecanoic acid (5-HD), 100 microM]. Contracture during ischemia (end-diastolic pressure) and functional recovery on reperfusion (developed pressure) were assessed. Total [Ca(2+)]i and [Ca(2+)]m were measured using indo 1 fluorescence. Both PC and diazoxide limited the increase in end-diastolic pressure and resulted in greater functional recovery after 30 min of reperfusion, functional effects that were partially or completely abolished by 5-HD. PC and diazoxide also significantly limited the increase in [Ca(2+)]m during ischemia-reperfusion. In addition, PC lowered [Ca(2+)]i during reperfusion, whereas diazoxide paradoxically resulted in increased [Ca(2+)]i during reperfusion. There was an inverse linear relationship between [Ca(2+)]m and developed pressure during reperfusion. PC limits the ischemia-induced increase in mitochondrial, but not total, [Ca(2+)]i, an effect mediated by opening mitochondrial K(ATP) channels. These data suggest that the lowering of mitochondrial calcium overload is a mechanism of cardioprotection in PC.

Cardioprotective effect of preconditioning is more efficient than postconditioning in rats submitted to cardiac ischemia and reperfusion

“…The opening these channels involves the epsilon isoform of protein kinase C (PKCε) 18 , preventing hyperpolarization of electrical potential of mitochondrial membrane 19 avoiding accumulation of mitochondrial Ca 2+ , prolonged opening of MPTP, release of cytochrome c and apoptosis 20,21 .…”

Hypoxia Inducible Factor-2α Stabilization and Maxi-K + Channel β 1 -Subunit Gene Repression by Hypoxia in Cardiac Myocytes

“…Although the involvement of mitochondrial K channels in cardioprotection is an issue under debate, 47 a common view is that opening of maxi-K and/or KATP channels produce K ϩ influx into the mitochondrial matrix, depolarizing the membrane and impeding mitochondrial toxic Ca 2ϩ overload. 32,48 This increase of mitochondrial K conductance has been proposed to occur immediately after repeated short-lasting exposures to ischemia/reperfusion and, therefore, without the need of transcriptional gene regulation. The maxi-K ␤ 1 gene inhibition required sustained (Ͼ8 hours) exposure to hypoxia, a condition incompatible with maintained opening of the large conductance maxi-K channels because this could lead to collapse of the mitochondrial membrane potential and, eventually, cell death.…”

Mitochondrial K channels in cell survival and death

“…It was proposed that this effect could be through a partial depolarization (in the magnitude of ∼10-24 mV) of ΔΨ m in response to mitoK ATP openers. Wang et al [78] has shown that mitoK ATP opening attenuates the mitochondrial Ca 2+ accumulation during ischemia in intact hearts. Similar observations were reported by Murata et al [79] who showed that mitoK ATP opening attenuated mitochondrial Ca 2+ accumulation during ischemia.…”