Postischemic recovery of heart metabolism and function: role of mitochondrial fatty acid transfer

Postischemic recovery of contractile function is better in hearts from fasted rats than in hearts from fed rats. In this study, we examined whether feeding-induced inhibition of palmitate oxidation at the level of carnitine palmitoyl transferase I is involved in the mechanism underlying impaired recovery of contractile function. Hearts isolated from fasted or fed rats were submitted to no-flow ischemia followed by reperfusion with buffer containing 8 mM glucose and either 0.4 mM palmitate or 0.8 mM octanoate. During reperfusion, oxidation of palmitate was higher after fasting than after feeding, whereas oxidation of octanoate was not influenced by the nutritional state. In the presence of palmitate, recovery of left ventricular developed pressure was better in hearts from fasted rats. Substitution of octanoate for palmitate during reperfusion enhanced recovery of left ventricular developed pressure in hearts from fed rats. However, the chain length of the fatty acid did not influence diastolic contracture. The results suggest that nutritional variation of mitochondrial fatty acid transfer may influence postischemic recovery of contractile function.

Effect of transient ischemia on the expression of glucose transporters GLUT-1 and GLUT-4 in rat myocardium

A number of observations indicate that myocardial glucose utilization is increased late during post-ischemic reperfusion. The present study was designed to examine whether transient ischemia elicits altered expression of glucose transporters GLUT-1 and GLUT-4. In rats, the left anterior descending coronary artery was occluded for 20 min followed by reperfusion for 1, 3 or 7 days. Regional myocardial uptake and phosphorylation of glucose was determined based on myocardial accumulation of 2-deoxy-D-[2, 6-3H]glucose-6-phosphate. In hearts from fasted rats, after 3 days of reperfusion, myocardial uptake and phosphorylation of glucose was 48% higher in the reperfused region compared to a remote control region. No regional difference in myocardial glucose uptake and phosphorylation was detectable in hearts from fed rats. After 1 day of reperfusion, expression of myocardial glucose transporter GLUT-1 mRNA was increased to 195+/-24% (mean+/-SEM) of the value measured in the remote region and the expression of GLUT-4 mRNA was decreased to 58+/-7%. After 3 days of reperfusion both mRNA and protein of GLUT-1 were higher in the reperfused region, averaging 133+/-23% and 249+/-36%, respectively. The corresponding values for GLUT-4 mRNA and protein were 77+/-7% and 62+/-6%, respectively. The results indicate that a short period of ischemia alters the expression of glucose transporter isoforms GLUT-1 and GLUT-4. Observed changes may be involved in the mechanisms underlying late changes of substrate metabolism during reperfusion.

[Cellular recovery after ischemia: physiopathologic aspects]

Myocytes that have survived a period of transient ischemia may present prolonged alterations of cellular function, detectable during several days. The early period of postischemic reperfusion is characterized by restoration of ion homeostasis mediated by rapid resumption of function of ion pumps (Na+/K(+)-ATPase, Ca(2+)-ATPase) and transsarcolemmal ion exchange mechanisms (H+/Na+, Na+/Ca2+ exchangers). There is experimental evidence that cellular injury may be enhanced during the initial seconds or minutes of reperfusion, depending on the conditions of reperfusion. During the late phase of reperfusion mRNA expression of a number of key proteins of myocyte function is altered. The pattern of gene expression during reperfusion exhibits features of cellular adaptation and/or dedifferentiation in addition to cell repair.