Compartmentation of glycolysis and glycogenolysis in the perfused rat heart

Developing methods that can detect compartmentation of metabolic pathways in intact tissues may be important for understanding energy demand and supply. In this study, we investigated compartmentation of glycolysis and glycogenolysis in the isolated perfused rat heart using (13)C NMR isotopomer analysis. Rat hearts previously depleted of myocardial glycogen were perfused with 5.5 mm [U-(13)C]glucose plus 50 mU/mL insulin until newly synthesized glycogen recovered to new steady-state levels ( approximately 60% of pre-depleted values). After a short wash-out period, the perfusate glucose was then switched to [1-(13)C]glucose, and glycolysis and glycogenolysis were stimulated by addition of glucagon (1 microg/ml). A (13)C NMR multiplet analysis of the methyl resonance of lactate provided an estimate of pyruvate derived from glucose vs glycogen while a multiplet analysis of the C4 resonance of glutamate provided an estimate of acetyl-CoA derived from glycolytic pyruvate vs glycogenolytic pyruvate. These two indices were not equivalent and their difference was further magnified in the presence of insulin during the stimulation phase. These combined observations are consistent with functional compartmentation of glycolytic and glycogenolytic enzymes that allows pyruvate generated by these two processes to be distinguished at the level of lactate and acetyl-CoA.