Increased mitochondrial calcium coexists with decreased reperfusion injury in postconditioned (but not preconditioned) hearts

Abstract

Ovize M. Increased mitochondrial calcium coexists with decreased reperfusion injury in postconditioned (but not preconditioned) hearts. Am J Physiol Heart Circ Physiol 294: H386-H391, 2008. First published October 19, 2007 doi:10.1152 doi:10. /ajpheart.01035.2007 is the main trigger for mitochondrial permeability transition pore opening, which plays a key role in cardiomyocyte death after ischemia-reperfusion. We investigated whether a reduced accumulation of mitochondrial Ca 2ϩ might explain the attenuation of lethal reperfusion injury by postconditioning. Anesthetized New Zealand White rabbits underwent 30 min of ischemia, followed by either 240 (infarct size protocol) or 60 (mitochondria protocol) min of reperfusion. They received either no intervention (control), preconditioning by 5-min ischemia and 5-min reperfusion, postconditioning by four cycles of 1-min reperfusion and 1-min ischemia at the onset of reflow, or pharmacological inhibition of the transition pore opening by N-methyl-4-isoleucine-cyclosporin (NIM811; 5 mg/kg iv) given at reperfusion. Area at risk and infarct size were assessed by blue dye injection and triphenyltetrazolium chloride staining. Mitochondria were isolated from the risk region for measurement of 1) Ca 2ϩ retention capacity (CRC), and 2) mitochondrial content of total (atomic absorption spectrometry) and ionized (potentiometric technique) calcium concentration. CRC averaged 0.73 Ϯ 0.16 in control vs. 4.23 Ϯ 0.17 g Ca 2ϩ /mg proteins in shams (P Ͻ 0.05). Postconditioning, preconditioning, or NIM811 significantly increased CRC (P Ͻ 0.05 vs. control). In the control group, total and free mitochondrial calcium significantly increased to 2.39 Ϯ 0.43 and 0.61 Ϯ 0.10, respectively, vs. 1.42 Ϯ 0.09 and 0.16 Ϯ 0.01 g Ca 2ϩ /mg in sham (P Ͻ 0.05). Surprisingly, whereas total and ionized mitochondrial Ca 2ϩ decreased in preconditioning, it significantly increased in postconditioning and NIM811 groups. These data suggest that retention of calcium within mitochondria may explain the decreased reperfusion injury in postconditioned (but not preconditioned) hearts. ischemia; preconditioning; mitochondria; myocardial infarction ZHAO ET AL. RECENTLY REPORTED that repeated cycles of brief reperfusion and ischemia performed immediately at the onset of reperfusion following a prolonged ischemic insult dramatically limited infarct size. They named this phenomenon "postconditioning" (59). This cardioprotection, which is as powerful as ischemic preconditioning, has now been reported in several experimental preparations (9,35,56). Reports indicate that postconditioning may require activation of several kinases, including phosphatidylinositol 3-kinase, Akt, ERK1/2, PKC-ε, and GSK-3␤, as well as guanylyl-cyclase and endothelial nitric oxide synthase (8,11,19,33,49,55,58). Our laboratory recently demonstrated in the rabbit heart that ischemic postconditioning inhibits mitochondrial permeability transition pore (mPTP) opening, in keeping with data showing that cyclosporine A (CsA), a pharmacological inhibit...

Redox balance and cardioprotection

“…On the contrary, in non- It is of note that, though PostC affects structural features of mitochondria, it does not influence mitochondrial respiration [154]. In particular, in mitochondria isolated from PostC hearts basal state 4 or ADP-stimulated state 3 respirations are not affected, thus excluding uncoupling or inhibition of the respiratory chain as a mechanism of mPTP inhibition [4]. Nevertheless, while basal respiration was not affected, ADP-stimulated respiration was increased after pharmacological PostC with morphine [145].…”

Diazoxide postconditioning induces mitochondrial protein S-Nitrosylation and a redox-sensitive mitochondrial phosphorylation/translocation of RISK elements: no role for SAFE

“…Mitochondrial and cytosolic fractions were obtained by a modification of published procedures [3,10]. In brief, the left ventricle was quickly submerged in 250 mM mannitol, 0.5 mM EGTA, 5 mM HEPES, and 0.1% (w/v) BSA (pH 7.4).…”

Inhibition of mitochondrial permeability transition pore opening: the holy grail of cardioprotection

“…Given proper determination of respiration, it is then essential to observe a true return of the extramitochondrial calcium concentration back to baseline to make sure that all mitochondria in the given population under study still have their MPTP closed, before after several calcium pulses with return to baseline an abrupt and massive calcium release is detected [6]. The comparison of mitochondrial preparations undergoing different interventions by the amount of calcium needed to induce MPTP opening assumes that baseline calcium load is comparable; in fact, reperfusion per se increases mitochondrial calcium, and preconditioning but not postconditioning attenuates this increase [1]. The administration of exogenous cyclosporine A and the consequent delay of MPTP opening should be part of each protocol to determine mitochondrial calcium retention capacity.…”