Myocardial energy metabolism in ischemic preconditioning and cardioplegia: A metabolic control analysis

Abstract

For both, cardioplegia (CP) and ischemic preconditioning (IP), increased ischemic tolerance with reduction in infarct size is well documented. These cardioprotective effects are related to a limitation of high energy phosphate (HEP) depletion. As CP and IP have to be assumed to act by different mechanisms, their effects on myocardial HEP metabolism cannot be assumed to be identical. Therefore, a systematic analysis of myocardial HEP metabolism for both procedures and their combination was performed, addressing the question whether there are different effects on myocardial HEP metabolism by IP and CP. In this study, metabolic control analysis was used to analyze the regulation of HEP metabolism. In open chest pigs subjected to 45 min LAD occlusion (index ischemia), CP and IP preserved myocardial ATP (control (C) 0.14 +/- 0.05 micromol/g wwt; CP: 0.95 +/- 0.14, IP: 0.61 +/- 0.12; p<0.05 C vs. CP and IP) and reduced myocardial necrosis (infarct size IA/RA: C: 90.0 +/- 3.0%; CP: 0.0 +/- 0.0% but patchy necroses; IP: 5.05 +/- 2.1%; p<0.05 C vs. CP and IP). The effects on HEP metabolism, however, were different: CP acted predominantly by slowing down the breakdown of phosphocreatine (PCr) during early phases of ischemia (C: DeltaPCr 0-2 min: 5.24 +/- 0.32 micromol/g wwt; CP: DeltaPCr 0-2 min: 3.38 +/- 0.23 micromol/g wwt, p<0.05 vs. C), leaving ATP breakdown during later stages unaffected (C: DeltaATP 5-45 min: 1.77 +/- 0.11 micromol/g wwt CP: DeltaATP 5-45 min: 1.59 +/- 0.28 micromol/g wwt, n.s. vs. C). In contrast to CP, in IP PCr breakdown was even increased (IP: DeltaPCr 0-2 min: 7.06 +/- 0.34 micromol/g wwt, p<0.05 vs. C), but ATP depletion greatly attenuated (IP: DeltaATP 5-45 min: 0.48 +/- 0.10 micromol/g wwt, p<0.05 vs. C and CP). Combining IP and CP yielded an additive effect with slowing down the breakdown of both PCr (IP+CP: DeltaPCr 0-2 min: 5.09+/- 0.35 micromol/g wwt, p<0.05 vs. C and IP) and ATP (IP+CP: DeltaATP 5-45 min: 0.56 +/- 0.48 micromol/g wwt, p<0.05 vs. C and CP), resulting in a higher ATP content at the end of index ischemia (1.86 +/- 0.46 micromol/g wwt, p<0.05 vs. C, CP and IP). Compared to IP, combining IP+CP achieved also a further reduction in infarct size (IA/RA: 0.0 +/- 0.0%, p<0.05 vs IP) and--compared to CP--a disappearance of the patchy necroses. The concept of major differences in myocardial HEP metabolism during CP and IP is further supported at a molecular level by metabolic control analysis. CP but not IP slowed down the CK reaction velocity at high PCr levels. In contrast to CP exerting a continuous decline in vATPase for any given ATP level, in IP myocardium ATPase reaction velocity was even increased at higher ATP contents, whereas a marked decrease in ATPase reaction velocity was found if ATP levels decreased. The equilibrium of the CK-reaction remained unchanged following CP, whereas IP induced a changing CK equilibrium, which was the more shifted towards PCr the more myocardial HEP content decreased. The data demonstrate different effects of CP and IP on myocardial HEP metab...

Modulation of the Protein Kinase Cδ Interaction with the “d” Subunit of F1F0-ATP Synthase in Neonatal Cardiac Myocytes

“…This could contribute protection by reducing ATP hydrolysis after ischemic insults. There have also been reports that PC induces an improved recovery of cardiac ATP levels following prolonged IR injury (10,15,16). This is consistent with the hypothesis that cardiac PC may improve F 1 F 0 -ATP synthase-mode activity as well.…”

“…It should be noted that four different F 1 F 0 -ATPase preparations, three different PKC preparations, and two different lots of peptides were used to obtain the data shown in Fig. 1, B-D. A major finding of our study was that one of the peptides (NH 2 -2 AGRKLALKTID-WVSF 16 -COOH) demonstrated a dose-dependent inhibition of the PKC␦-dF 1 F 0 binding interaction (Fig. 1B).…”

“…Each peptide included either the PKC␦-dF 1 F 0 interaction antagonist NH 2 -2 AGRKLALKTIDWVSF 16 -COOH or agonist NH 2 -was also placed at the N terminus of each peptide using a cysteine-cysteine linkage as described previously (30). Following the Tat sequence, we included a mitochondrial targeting sequence (MLATRALSLIGKRAISTSVC) derived from the number IV subunit of cytochrome oxidase (31).…”

An Inhibitor of the δPKC Interaction with the d Subunit of F1Fo ATP Synthase Reduces Cardiac Troponin I Release from Ischemic Rat Hearts: Utility of a Novel Ammonium Sulfate Precipitation Technique

“…At present the preferred protein used for this purpose is cardiac troponin I (cTnI) [4]–[6]. cTnI is a myofibrillar protein which complexes with tropomyosin and troponins T and C to minimize Ca ++ binding to troponin C, and prevent subsequent crossbridge formation between the actin and myosin myofilaments [7].…”

“…Previous studies have proposed that cardiac preconditioning (PC), a cardio-protective response against IR injury, inhibits F 1 Fo ATPase-mode activity [24], [25], which may contribute protection by reducing ATP hydrolysis after ischemic insults. There have also been reports that PC induces an improved recovery of cardiac ATP levels following prolonged IR injury [1], [2], [6]. The F 1 Fo complex therefore, has the potential to impact thousands of energy-requiring processes that contribute to normal cardiac functioning and IR injury.…”