Calcium-mediated activation of pyruvate dehydrogenase in severely injured postischemic myocardium

Jerome Terrand, Irene Papageorgiou, Nathalie Rosenblatt-Velin, Rene Lerch
2001 American Journal of Physiology. Heart and Circulatory Physiology  
Terrand, Jerome, Irene Papageorgiou, Nathalie Rosenblatt-Velin, and Rene Lerch. Calcium-mediated activation of pyruvate dehydrogenase in severely injured postischemic myocardium. Am J Physiol Heart Circ Physiol 281: H722-H730, 2001.-Indirect evidence suggests that activity of pyruvate dehydrogenase (PDH) influences recovery of the myocardium after transient ischemia. The present study examined the relationship between postischemic injury and activity of PDH and the role of mitochondrial calcium
more » ... uptake for observed changes in PDH activity. Isovolumically beating isolated rat hearts perfused with erythrocyte-enriched buffer containing glucose, palmitate, and insulin were submitted to either 20 or 35 min of no-flow ischemia. After 20 min of no-flow ischemia, hearts exhibited complete recovery of developed left ventricular pressure (DLVP). The proportion of myocardial PDH in the active state was modestly increased to 38% (compared with 13% in control hearts) without a change in glucose oxidation. In contrast, in hearts subjected to 35 min of no-flow ischemia (which exhibited poor recovery of DLVP), there was marked stimulation of glucose oxidation (ϩ460%; P Ͻ 0.01) and pronounced increase in the active fraction of PDH to 72% (P Ͻ 0.01). Glycolytic flux was not significantly altered. Ruthenium red (6 M) completely abolished the activation of PDH and the increase in glucose oxidation. The results indicate that variable stimulation of glucose oxidation during reperfusion is related to different degrees of activation of PDH, which depends on the severity of the ischemic injury. Activation of PDH seems to be mediated by myocardial calcium uptake. reperfusion; substrate; metabolism; perfused heart; ruthenium red IN RECENT YEARS evidence has accumulated that metabolism of exogenous glucose early during reperfusion favorably influences recovery of postischemic myocardium (22, 42) . Identification of the subcellular mechanism(s) responsible for the beneficial effects of glucose metabolism is complicated by the multiple fates of glucose taken up by the myocardium, which include incorporation into glycogen, anaerobic glycolysis to lactate, mitochondrial oxidation, and oxidation in the pentosephosphate pathway (6). A number of observations suggest a crucial role of activation of pyruvate dehydrogenase (PDH) for the protective effect of glucose (19). PDH largely controls the rate of entry of pyruvate into mitochondrial oxidative catabolism by the tricarboxylic acid cycle. It has been proposed (39) that oxidation of glycolytically produced pyruvate avoids the production of protons during anaerobic glycolysis to lactate and thereby reduces myocyte calcium overload caused by successive transsarcolemmal H ϩ / Na ϩ and Na ϩ /Ca 2ϩ exchange. Activity of PDH is reduced by phosphorylation, which is mediated by PDH kinase. The latter enzyme is activated by high levels of acetyl coenzyme A (acetyl-CoA) and NADH, as is observed in myocardium under conditions of high fatty acid oxidation (33), and is inhibited by dichloroacetate (35). Conversely, PDH is activated by a calcium-sensitive PDH phosphatase (25). Consistent with a protective effect of activation of PDH during reperfusion, enhancement of glucose oxidation and improvement of recovery of contractile function has been observed in postischemic hearts exposed to pyruvate (16), dichloroacetate (27), trimetazidine (43), L-carnitine (38), and ranolazine (5). However, the rationale for implementation of an intervention aimed at activation of PDH early during reperfusion depends on the level of spontaneous activity of PDH in postischemic myocardium. In fact, reported data on carbohydrate oxidation early during reperfusion exhibit considerable variability with increased (9), unaltered (17, 20), or decreased (14, 38) glucose oxidation compared with baseline values. This suggests that activity of PDH early during reperfusion critically depends on the selected experimental conditions. Specifically, in the experiments by Lopaschuks et al. (27), in isolated working rat hearts perfused with medium containing 11 mM glucose and 1.2 mM palmitate, glucose oxidation rapidly returned to the preischemic level after 25-30 min of no-flow ischemia, which was markedly lower than in control hearts perfused with glucose as the sole substrate. This indirectly suggests persistent fatty acid-mediated inhibition of PDH during reperfusion. The concept of postischemic inhibition of PDH has been supported by 13 C magnetic resonance spectroscopy (16) or direct measurement of myocardial enzyme activity in isolated perfused rat hearts subjected to 10 or 20 min of no-flow ischemia
doi:10.1152/ajpheart.2001.281.2.h722 pmid:11454576 fatcat:nvyh64unk5fhjdtn2dcvtwrpte