Discrepancy between GLUT4 translocation and glucose uptake after ischemia.
OBJECTIVE
Low-flow ischemia results in glucose transporter translocation and in increased glucose uptake. After total ischemia in rat heart, we found no increase in glucose uptake. Here we test the hypothesis that total ischemia is associated with decreased activation of GLUT4 despite translocation.


METHODS
Isolated working hearts (n=70, Sprague-Dawley rats) were perfused for 70 min at physiological workload with Krebs-Henseleit buffer containing [2-3H]glucose (5 mmol/l, 0.05 microCi/ml) with either oleate (0.4 mmol/l, 1%BSA) or pyruvate (5 mmol/l, 1%BSA). After 20 min, hearts were subjected to 15 min of total ischemia followed by 35 min of reperfusion. We measured glucose uptake and intracellular free glucose (IFG) using [2-3H]glucose and [14C]sucrose, and determined the distribution of GLUT4 by colocalization immunofluorescence with Na-K ATP-ase.


RESULTS
Cardiac power was 10.1 +/- 0.90 mW before ischemia and did not differ between groups. Recovery was the same in both groups (55.7 +/- 24.8%). Glucose uptake did not differ between groups before ischemia, and did not increase during reperfusion. Despite evidence of GLUT4 translocation after reperfusion in both groups, IFG did not increase compared with before ischemia.


CONCLUSIONS
We conclude that there is a discrepancy between glucose transporter availability and glucose uptake after ischemia, which may be due to inhibition of GLUT4 in the plasma membrane.
Zaha
Vlad
V
Department of Cardiovascular Surgery, Albert-Ludwigs-University of Freiburg, Freiburg, Germany.
Nitschke
Roland
R
Göbel
Heike
H
Fischer-Rasokat
Ulrich
U
Zechner
Christoph
C
Doenst
Torsten
T
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D006593:Hexokinase / Q000378:metabolism; D007511:Ischemia / Q000378:metabolism*; D008297:Male; D015425:Myocardial Reperfusion; D009206:Myocardium / Q000378:metabolism; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D051275:Glucose Transporter Type 4; D006593:Hexokinase; D000254:Sodium-Potassium-Exchanging ATPase; D005947:Glucose