The effect of K(atp)channel activation on myocardial cationic and energetic status during ischemia and reperfusion: role in cardioprotection

KATP channels are regulators of programmed cell death and targets for the creation of novel drugs against ischemia/reperfusion cardiac injury

BACKGROUND

The use of percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is associated with a mortality rate of 5%-7%. It is clear that there is an urgent need to develop new drugs that can effectively prevent cardiac reperfusion injury. ATP-sensitive K+ (KATP ) channel openers (KCOs) can be classified as such drugs.

RESULTS

KCOs prevent irreversible ischemia and reperfusion injury of the heart. KATP channel opening promotes inhibition of apoptosis, necroptosis, pyroptosis, and stimulation of autophagy. KCOs prevent the development of cardiac adverse remodeling and improve cardiac contractility in reperfusion. KCOs exhibit antiarrhythmic properties and prevent the appearance of the no-reflow phenomenon in animals with coronary artery occlusion and reperfusion. Diabetes mellitus and a cholesterol-enriched diet abolish the cardioprotective effect of KCOs. Nicorandil, a KCO, attenuates major adverse cardiovascular event and the no-reflow phenomenon, reduces infarct size, and decreases the incidence of ventricular arrhythmias in patients with acute myocardial infarction.

CONCLUSION

The cardioprotective effect of KCOs is mediated by the opening of mitochondrial KATP (mitoKATP ) and sarcolemmal KATP (sarcKATP ) channels, triggered free radicals' production, and kinase activation.

Effect of nicorandil on QT dispersion in patients with stable angina pectoris undergoing elective angioplasty: A triple-blind, randomized, placebo-controlled study

Background

Nicorandil leads to the relaxation of fine vascular smooth muscle, and thus causes vasodilatation of major epicardial. Also, it has anti-arrhythmic and cardio-protective effects by improving reperfusion, and ultimately leads to a reduction in microvascular damage caused by percutaneous coronary intervention (PCI).

Objective

The aim of this study was to determine the effect of nicorandil on QT interval dispersion (QTd) in patients with stable angina pectoris during elective angioplasty.

Methods

This triple-blind and randomized clinical trial was performed on patients with stable angina pectoris, candidates for elective angiography referred to Imam Reza and Ghaem hospitals in Mashhad, Iran, between January and October 2016. The patients were randomly assigned to one of two groups receiving nicorandil (60 mg as 20 mg before and 40 mg after PCI) and placebo. All the patients underwent electrocardiography 12 hours before and 12 hours after PCI. The values of maximal corrected QT interval (QTc max) and QTd in these intervals, and the levels of changes in the QTd (QTd difference before angiography and after PCI) were compared between the two groups. Data were analyzed statistically using SPSS version 18 software via Chi-square and Independent-samples t-test.

Results

This study was performed on 90 patients (55 males and 35 females) with a mean age of 58.6±10.8 years, on two groups of 45 people. The two groups were matched for age, body mass index, cardiovascular risk factors and baseline testing. The QTd before angiography had no statistically significant difference between the patients of both groups (control: 77.7±17.1 vs. nicorandil: 80.7±14.2 ms; p=0.371). The QTd after PCI in the nicorandil group was lower than the control group (48.1±14.2 vs. 59.2±15.6 ms; p=0.000). The decrease rate in QTd had a statistically significant difference between the two groups (control: 18.9±11.0 vs. nicorandil: 33.5±9.5 ms; p=0.000).

Conclusions

The results of this study showed that oral administration of nicorandil around the PCI could further reduce QTd following PCI, compared to the control group.

Trial registration

The trial was registered at the Iranian Registry of Clinical Trials (http://www.irct.ir) with the Irct ID: IRCT2016120631159N1

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

KATP Channels in the Cardiovascular System

KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.

Effect of nicorandil in patients with heart failure: a systematic review and meta-analysis

BACKGROUND AND PURPOSE

It is unclear whether nicorandil, a metabolic therapeutic drug, can be applied clinically to therapy of heart failure (HF). This meta-analysis evaluated therapeutic effects of nicorandil on HF patients.

EXPERIMENTAL APPROACH

We performed a systematic review and meta-analysis of published studies evaluating effect of nicorandil on HF patients. Studies were stratified according to controlled versus uncontrolled designs and analyzed using random-effects meta-analysis models.

KEY RESULTS

We identified a total of 20 studies with a total of 1222 patients. In five randomized controlled studies, nicorandil treatment resulted in reduction in all-cause mortality and hospitalization for cardiac causes (HR: 0.35, P < 0.001) and improved cardiac pump function (SMD: 0.31, P = 0.02). In 15 observational studies, nicorandil therapy increases cardiac pump function (SMD: 0.75, P < 0.001), improves NYHA functional class (WMD: -1.33, P < 0.001), decreases PCWP (WMD: -6.86 mm Hg, P < 0.001), and pulmonary arterial pressure (SMD: -0.84, P < 0.001).

CONCLUSIONS AND IMPLICATIONS

The use of nicorandil in HF patients exerts substantial beneficial effects, suggesting that it may be an additional therapeutic agent for HF.

Genetics and genomics of ischemic tolerance: focus on cardiac and cerebral ischemic preconditioning

A subthreshold ischemic insult applied to an organ such as the heart and/or brain may help to reduce damage caused by subsequent ischemic episodes. This phenomenon is known as ischemic tolerance mediated by ischemic preconditioning (IPC) and represents the most powerful endogenous mechanism against ischemic injury. Various molecular pathways have been implicated in IPC, and several compounds have been proposed as activators or mediators of IPC. Recently, it has been established that the protective phenotype in response to ischemia depends on a coordinated response at the genomic, molecular, cellular and tissue levels by introducing the concept of 'genomic reprogramming' following IPC. In this article, we sought to review the genetic expression profiles found in cardiac and cerebral IPC studies, describe the differences between young and aged organs in IPC-mediated protection, and discuss the potential therapeutic application of IPC and pharmacological preconditioning based on the genomic response.

The balance between inactivation and activation of the Na+-K+ pump underlies the triphasic accumulation of extracellular K+ during myocardial ischemia

Ischemia-induced hyperkalemia (accumulation of extracellular K(+)) predisposes the heart to the development of lethal reentrant ventricular arrhythmias. This phenomenon exhibits a triphasic time course and is thought to be mediated by a combination of three mechanisms: 1) increased cellular K(+) efflux, 2) decreased cellular K(+) influx, and 3) shrinkage of the extracellular space. These ischemia-induced electrophysiological changes are driven by an impaired cellular metabolism. However, the relative contributions of these mechanisms, as well as the origin of the triphasic profile, have proven to be difficult to determine experimentally. In this study, the changes in metabolite concentrations that arise during 15 min of zero-flow global ischemia were incorporated into a dynamic model of cellular electrophysiology, which was extended to include a metabolically sensitive description of the Na(+)-K(+) pump and ATP-sensitive K(+) channel, in addition to cell volume regulation. The coupling of altered K(+) fluxes and cell volume regulation enables an integrative simulation of ischemic hyperkalemia. These simulations were able to quantitatively reproduce experimental measurements of the accumulation of extracellular K(+) during 15 min of simulated ischemia, both with respect to the degree of K(+) loss as well as the triphasic time course. Analysis of the model indicates that the inhibition of the Na(+)-K(+) pump is the dominant factor underlying this hyperkalemic behavior, accounting for approximately 85% of the observed extracellular K(+) accumulation. It was found that the balance between activation and inhibition of the Na(+)-K(+) pump, affected by the changing metabolite and ion concentrations (in particular, [ADP]), give rise to the triphasic profile associated with ischemic hyperkalemia.

Mitochondria are targets for geranylgeranylacetone-induced cardioprotection against ischemia-reperfusion in the rat heart

It has been shown that orally administered geranylgeranylacetone (GGA), an anti-ulcer drug, induces expression of heat shock protein 72 (HSP72) and provides protection against ischemia-reperfusion in rat hearts. The underlying protective mechanisms, however, remain unknown. Mitochondria have been shown to be a selective target for heat stress-induced cardioprotection. Therefore, we hypothesized that preservation of mitochondrial function, owing to an opening of a putative channel in the inner mitochondrial membrane, the mitochondrial ATP-sensitive potassium (mitoK(ATP)) channel, could be involved in GGA- or heat stress-induced cardioprotection against ischemia-reperfusion. Rats were treated with oral GGA or vehicle. Twenty-four hours later, each heart was isolated and perfused with a Langendorff apparatus. GGA-treated hearts showed better functional recovery, and less creatine kinase was released during a 30-min reperfusion period, after 20 min of no-flow ischemia. Concomitant perfusion with 5-hydroxydecanoate (5-HD, 100 microM) or glibenclamide (10 microM) abolished the GGA-induced cardioprotective effect. GGA also showed preserved mitochondrial respiratory function, isolated at the end of the reperfusion period, which was abolished with 5-HD treatment. GGA prevented destruction of the mitochondrial structure by ischemia-reperfusion, as shown by electron microscopy. In cultured cardiomyocytes, GGA induced HSP72 expression and resulted in less damage to cells, including less apoptosis in response to hypoxia-reoxygenation. Treatment with 5-HD abolished the GGA-induced cardioprotective effects but did not affect HSP72 expression. Our results indicate that preserved mitochondrial respiratory function, owing to GGA-induced HSP72 expression, may, at least in part, have a role in cardioprotection against ischemia-reperfusion. These processes may involve opening of the mitoK(ATP) channel.

Effects of genetic deletion of angiotensin-(1-7) receptor Mas on cardiac function during ischemia/reperfusion in the isolated perfused mouse heart

In this study we investigated the role of Mas on cardiac function during ischemia/reperfusion in isolated perfused mouse heart. Following a stabilization period of 30 min, hearts from WT and Mas KO mice were subjected to global ischemia. After 20 min of ischemia, the flow was restarted and the hearts were reperfused for 30 min. An additional group of WT mice was perfused with solution containing the Ang-(1-7) receptor Mas antagonist A-779. Isolated heart of Mas KO and WT treated with A-779 presented an increase in the perfusion pressure in the baseline period. This difference increased with 5 min of reperfusion reaching similar values to baseline period at the end of the reperfusion. Isolated hearts of Mas KO and WT treated with A-779 also presented a decreased systolic tension, +/-dT/dt, and HR. Upon global ischemia WT hearts showed a significant decrease in systolic tension and an increase in diastolic tension. During reperfusion an increase in systolic and diastolic tension was observed in WT mice. Deletion or blockade of Mas markedly attenuated these changes in isolated hearts. These results indicate that Mas plays an important role in cardiac function during ischemia/reperfusion which is in keeping with the cardiac and coronary effects previously described for Ang-(1-7).

Progress towards a more physiologic approach to donor heart preservation: the advantages of hyperpolarized arrest

BACKGROUND

The University of Wisconsin (UW) solution is the gold standard for heart preservation but has limitations in terms of both duration and adequacy of protection. Our laboratory has been interested in a more physiologic approach to heart preservation by maintaining the heart at its resting membrane potential (hyperpolarized arrest) with the K(ATP) channel agonist pinacidil. This study compared our extracellular solution (WashU) with the UW intracellular depolarizing solution and quantified the protective effect of pinacidil in both solutions.

METHODS

Thirty-two rabbit hearts received 1 of 4 solutions in a crystalloid-perfused Langendorff apparatus: (1) UW, (2) WashU containing 0.5 mmol/liter pinacidil, (3) UW with 0.5 mmol/liter pinacidil, or (4) WashU without pinacidil. Thirty minutes of perfusion was followed by data acquisition consisting of left ventricular pressure-volume curves generated by inflating an intraventricular balloon. All hearts were placed in cold storage for 8 hours, followed by 1 hour of reperfusion before data acquisition.

RESULTS

Post-ischemic developed pressure (DP) was better preserved by WashU (76.8% +/- 3.8%) than by UW (48.3% +/- 2.5%). Diastolic compliance was better preserved by WashU (239.9% +/- 77.2%) compared with UW (711.1% +/- 193.1%). Removing pinacidil from our solution resulted in decreased DP (46.6% +/- 3.2%) and diastolic compliance (688.8% +/- 158.2%) Adding pinacidil to UW had a limited effect on DP and compliance.

CONCLUSIONS

Our results support the superiority of the WashU hyperpolarizing solution for heart preservation over UW. Pinacidil was beneficial in maintaining cardiac function and compliance. This benefit was not observed when pinacidil was placed into the UW depolarizing solution.

Donor heart preservation with pinacidil: the role of the mitochondrial K ATP channel

BACKGROUND

Pinacidil solutions have been shown to have significant cardioprotective effects. Pinacidil activates both sarcolemmal and mitochondrial potassium-adenosine triphosphate (K(ATP)) channels. This study was undertaken to compare pinacidil solution with University of Wisconsin (UW) solution and to determine if the protective effect of pinacidil involved mitochondrial or sarcolemmal K(ATP) channels.

METHODS

Thirty-two rabbit hearts received one of four preservation solutions in a Langendorff apparatus: (1) UW; (2) a solution containing 0.5 mmol/L pinacidil; (3) pinacidil with Hoechst-Marion-Roussel 1098 (HMR-1098), a sarcolemmal channel blocker; and (4) pinacidil with 5-hydroxydecanote, a mitochondrial channel blocker. Left ventricular pressure-volume curves were generated by an intraventricular balloon. All hearts were placed in cold storage for 8 hours, followed by 60 minutes of reperfusion.

RESULTS

Postischemic developed pressure was better preserved by pinacidil than by UW. This cardioprotective effect was eliminated by 5-hydroxydecanote and diminished by HMR-1098. Diastolic compliance was better preserved by pinacidil when compared with UW. This protection was abolished by the addition of 5-hydroxydecanote and moderately decreased by HMR-1098.

CONCLUSIONS

Our results support the superiority of pinacidil over UW after 8 hours of storage. The cardioprotective role of pinacidil is mediated primarily by the mitochondrial K(ATP) channel.

Fasudil prevents KATP channel-induced improvement in postischemic functional recovery

Whereas activation of ATP-dependent potassium (K(ATP)) channels greatly improves postischemic myocardial recovery, the final effector mechanism for K(ATP) channel-induced cardioprotection remains elusive. RhoA is a GTPase that regulates a variety of cellular processes known to be involved with K(ATP) channel cardioprotection. Our goal was to determine whether the activity of a key rhoA effector, rho kinase (ROCK), is required for K(ATP) channel-induced cardioprotection. Four groups of perfused rat hearts were subjected to 36 min of zero-flow ischemia and 44 min of reperfusion with continuous measurements of mechanical function and (31)P NMR high-energy phosphate data: 1) untreated, 2) pinacidil (10 microM) to activate K(ATP) channels, 3) fasudil (15 microM) to inhibit ROCK, and 4) both fasudil and pinacidil. Pinacidil significantly improved postischemic mechanical recovery [39 +/- 16 vs. 108 +/- 4 mmHg left ventricular diastolic pressure (LVDP), untreated and pinacidil, respectively]. Fasudil did not affect reperfusion LVDP (41 +/- 13 mmHg) but completely blocked the marked improvement in mechanical recovery that occurred with pinacidil treatment (54 +/- 15 mmHg). Substantial attenuation of the postischemic energetic recovery was also observed. These data support the hypothesis that ROCK activity plays a role in K(ATP) channel-induced cardioprotection.

Nicorandil: a review of its use in the management of stable angina pectoris, including high-risk patients

Nicorandil (Adancor, Angicor, Dancor, Nikoril [Europe], Ikorel [Europe and Oceania], Sigmart [Japan, Korea and Taiwan]) is an adenosine triphosphate (ATP)-sensitive potassium (KATP) channel agonist with nitrate-like properties used in the management of stable angina pectoris. With well established monotherapeutic antianginal activity and a beneficial effect (when added to optimal antianginal therapy) on clinical outcomes in high-risk patients with stable angina, twice-daily oral nicorandil is a useful alternative or addition to other antianginal therapy.

Difference in the cardioprotective mechanisms between ischemic preconditioning and pharmacological preconditioning by diazoxide in rat hearts

BACKGROUND

Recent studies have implicated the opening of mitochondrial K(ATP) (mitoK(ATP)) channels and the production of reactive oxygen species (ROS) in the cardioprotective mechanism of ischemic preconditioning (IPC).

METHODS AND RESULTS

The involvement of mitoK(ATP) channels and ROS in the cardioprotective effects of both IPC and the mitoK(ATP) channel opener diazoxide (DZ) was investigated in ischemic/reperfused rat hearts. The effects of IPC and DZ on myocardial high-energy phosphate concentrations and intracellular pH (pH(i)) were also examined using (31)P nuclear magnetic resonance spectroscopy. Although both the mitoK(ATP) channel inhibitor 5-hydroxydecanoate and the antioxidant N-acetylcysteine abolished the postischemic recovery of contractile function by DZ, neither of them inhibited that by IPC. IPC attenuated the decline in pHi during ischemia, but DZ did not (6.28+/-0.04 in IPC, p<0.05, and 6.02+/-0.05 in DZ vs 6.02 +/-0.06 in control hearts). DZ, but not IPC, reduced the decrease in ATP levels during ischemia (ATP levels at 20-min ischemia: 26.3+/-3.4% of initial value in DZ, p<0.05, and 8.1+/-3.0% in IPC vs 15.1+/-1.3% in control hearts).

CONCLUSIONS

These results suggest that DZ-induced cardioprotection is related to ROS production and reduced ATP degradation during ischemia, whereas attenuated acidification during ischemia is involved in IPC-induced cardioprotection, which is not mediated through mitoK(ATP) channel opening or ROS production.

Opening of mitochondrial K+ channels increases ischemic ATP levels by preventing hydrolysis

Mitochondrial ATP-sensitive K+ channels (mitoK(ATP)) have been proposed to mediate protection against ischemic injury by increasing high-energy intermediate levels. This study was designed to verify if mitochondria are an important factor in the loss of cardiac ATP associated to ischemia, and determine the possible role of mitoK(ATP) in the control of ischemic ATP loss. Langendorff-perfused rat hearts subjected to ischemia were found to have significantly higher ATP contents when pretreated with oligomycin or atractyloside, indicating that mitochondrial ATP hydrolysis contributes toward ischemic ATP depletion. MitoK(ATP) opening induced by diazoxide promoted a similar protection against ATP loss. Diazoxide also inhibited ATP hydrolysis in isolated, nonrespiring mitochondria, an effect accompanied by a drop in the membrane potential and Ca2+ uptake. In hearts subjected to ischemia followed by reperfusion, myocardial injury was prevented by diazoxide, but not atractyloside or oligomycin, which, unlike diazoxide, decreased reperfusion ATP levels. Our results suggest that mitoK(ATP)-mediated protection occurs due to selective inhibition of mitochondrial ATP hydrolysis during ischemia, without affecting ATP synthesis after reperfusion.

Nicorandil preserves mitochondrial function during ischemia in perfused rat heart

A possible mechanism for the action of nicorandil on the improvement of energy metabolism of ischemic/reperfused hearts was examined. Perfused rat hearts were subjected to 35-min ischemia/60-min reperfusion. The heart was treated with nicorandil at concentrations of 10 to 100 microM for the last 30-min of pre-ischemia. Nicorandil preserved the mitochondrial oxygen consumption rate during ischemia and attenuated the decrease in mitochondrial function during reperfusion in association with the enhanced post-ischemic recovery of the left ventricular developed pressure. To assess the direct effect on mitochondria, myocardial saponin-skinned bundles were incubated under hypoxic conditions in vitro. Hypoxia-induced decrease in the mitochondrial oxygen consumption rate was attenuated by treatment of the bundles with 100 microM nicorandil. This attenuation was abolished by the combined treatment with the K(ATP) channel blocker, 5-hydroxydecanoate (5-HD). These results suggest that nicorandil is capable of attenuating ischemia/reperfusion injury of isolated perfused hearts through preservation of mitochondrial function during ischemia.

Ischemic preconditioning improves mitochondrial tolerance to experimental calcium overload

BACKGROUND

Ca(2+) overload leads to mitochondrial uncoupling, decreased ATP synthesis, and myocardial dysfunction. Pharmacologically opening of mitochondrial K(ATP) channels decreases mitochondrial Ca(2+) uptake, improving mitochondrial function during Ca(2+) overload. Ischemic preconditioning (IPC), by activating mitochondrial K(ATP) channels, may attenuate mitochondrial Ca(2+) overload and improve mitochondrial function during reperfusion. The purpose of these experiments was to study the effect of IPC (1) on mitochondrial function and (2) on mitochondrial tolerance to experimental Ca(2+) overload.

METHODS

Rat hearts (n = 6/group) were subjected to (a) 30 min of equilibration, 25 min of ischemia, and 30 min of reperfusion (Control) or (b) two 5-min episodes of ischemic preconditioning, 25 min of ischemia, and 30 min of reperfusion (IPC). Developed pressure (DP) was measured. Heart mitochondria were isolated at end-Equilibration (end-EQ) and at end-Reperfusion (end-RP). Mitochondrial respiratory function (state 2, oxygen consumption with substrate only; state 3, oxygen consumption stimulated by ADP; state 4, oxygen consumption after cessation of ADP phosphorylation; respiratory control index (RCI, state 3/state 4); rate of oxidative phosphorylation (ADP/Deltat), and ADP:O ratio) was measured with polarography using alpha-ketoglutarate as a substrate in the presence of different Ca(2+) concentrations (0 to 5 x 10(-7) M) to simulate Ca(2+) overload.

RESULTS

IPC improved DP at end-RP. IPC did not improve preischemic mitochondrial respiratory function or preischemic mitochondrial response to Ca(2+) loading. IPC improved state 3, ADP/Deltat, and RCI during RP. Low Ca(2+) levels (0.5 and 1 x 10(-7) M) stimulated mitochondrial function in both groups predominantly in IPC. The Control group showed evidence of mitochondrial uncoupling at lower Ca(2+) concentrations (1 x 10(-7) M). IPC preserved state 3 at high Ca(2+) concentrations.

CONCLUSIONS

The cardioprotective effect of IPC results, in part, from preserving mitochondrial function during reperfusion and increasing mitochondrial tolerance to Ca(2+) loading at end-RP. Activation of mitochondrial K(ATP) channels by IPC and their improvement in Ca(2+) homeostasis during RP may be the mechanism underlying this protection.

Mitochondrial function during ischemic preconditioning

Background. Ischemic preconditioning (IPC) protects the myocardium from ischemia reperfusion injury. The effect of IPC on the mitochondria is not well known. However, one of the mechanisms postulated in IPC (the opening of the mitochondrial K(ATP) channels) is likely to result in changes in mitochondrial function. Therefore, the purpose of this study was to determine the effect of IPC on mitochondrial function during ischemia reperfusion. Methods. Isolated rat hearts (n = 6/group) were subjected to (1) 30 minutes of equilibration, 25 minutes of ischemia, and 30 minutes of reperfusion (RP) (control group) or (2) 10 minutes of equilibration, two-5 minute episodes of IPC (each followed by 5 minutes of re-equilibration), 25 minutes of ischemia, and 30 minutes of RP (IPC group). Left ventricular rate pressure product (RPP) was measured. At end-equilibration (end-EQ) and at end-reperfusion (end-RP) mitochondria were isolated. Mitochondrial respiratory function (state 2, 3, and 4), respiratory control index (RCI), rate of oxidative phosphorylation (ADP/Delta t), and ADP:O ratio were measured by polarography with the use of NADH- or FADH-dependent substrates. Results. IPC improved recovery of RPP at end-RP (72% +/- 5% in IPC vs 30% +/- 4% in control, P <.05). Ischemia reperfusion (IR) decreased state 3, ADP/Delta t, and RCI in both groups compared with end-EQ. IPC improved state 3 (47 +/- 3 in IPC vs 37 +/- 2 ng-atoms O/min/mg protein in control), ADP/Delta t (17 +/- 1 in IPC vs 13 +/- 1 nmol/s/mg protein in control), and RCI (3.7 +/- 0.1 in IPC vs 2.1 +/- 0.2 in control) at end-RP compared with control with the use of NADH-dependent substrate (P <.05 vs control). IPC also improved state 3 (85 +/- 6 in IPC vs 71 +/- 4 ng-atoms O/min/mg protein in control), ADP/Delta t (18 +/- 2 in IPC vs 12 +/- 1 nmol/s/mg protein in control), RCI (2 +/- 0.1 in IPC vs 1.5 +/- 0.1 in control), and ADP:O ratios (1.4 +/- 0.04 in IPC vs 1.7 +/- 0.09 in control) at end-RP compared with control with the use of FADH-dependent substrate (P <.05 vs control). Conclusions. The cardioprotective effects of IPC can be attributed at least in part to the preservation of mitochondrial function during reperfusion.