Dissociation of glucose tracer uptake and glucose transporter distribution in the regionally ischaemic isolated rat heart: application of a new autoradiographic technique.

Fluorine-18 fluoro-2-deoxyglucose ((18)FDG) and carbon-14 2-deoxyglucose ((14)C-2-DG) are both widely used tracers of myocardial glucose uptake and phosphorylation. We have recently shown, using positron emission tomography (PET) and nuclear magnetic resonance, that ischaemia-reperfusion (I-R) causes differential changes in their uptake. We describe here the novel application of an autoradiographic technique allowing the investigation of this phenomenon at high resolution, using tracer concentrations of both analogues in the dual-perfused isolated rat heart. We also investigate the importance of glucose transporter (GLUT 1 and GLUT 4) distribution in governing the observed phosphorylated analogue accumulation. Hearts ( n=5) were perfused with Krebs buffer for 40 min, made regionally zero-flow ischaemic for 40 min and reperfused for 60 min with Krebs containing tracer (18)FDG (200 MBq) and tracer (14)C-2-DG (0.37 MBq). Hearts were then frozen and five sections (10 micro m) were cut per heart, fixed and exposed on phosphor storage plates for 18 h (for (18)FDG) and then for a further 9 days (for (14)C-2-DG). Quantitative digital images of tracer accumulation were obtained using a phosphor plate reader. The protocol was repeated in a second group of hearts and GLUT 1 and GLUT 4 distribution analysed. Post-ischaemic accumulation of (18)FDG-6-P was inhibited by 38.2%+/-1.7% and (14)C-DG-6-P by 19.0%+/-2.2%, compared with control ( P<0.05). After placing seven "lines of interrogation" across each heart section and analysing the phosphorylated tracer accumulation along them, a transmural gradient of both tracers was observed; this was highest at the endocardium and lowest at the epicardium. GLUT 4 translocated to the sarcolemma in the ischaemic/reperfused region (from 24%+/-3% to 59%+/-5%), while there was no cellular redistribution of GLUT 1. We conclude that since decreased phosphorylated tracer accumulation occurs after ischaemia-reperfusion, despite greater externalisation of GLUT 4, hexokinase or the affinities of the GLUT transporters are changed under these conditions.