Assessment of glycogen turnover in aerobic, ischemic, and reperfused working rat hearts.

Glycogen and its turnover are important components of myocardial glucose metabolism that significantly impact on postischemic recovery. We developed a method to measure glycogen turnover (rates of glycogen synthesis and degradation) in isolated working rat hearts using [3H]- and [14C]glucose. In aerobic hearts perfused with 11 mM glucose, 1.2 mM palmitate, and 100 μU/ml insulin, rates of glycogen synthesis and degradation were 1.24 ± 0.3 and 0.53 ± 0.25 μmol ⋅ min-1 ⋅ g dry wt-1, respectively. Low-flow ischemia (0.5 ml/min, 60 min) elicited a marked glycogenolysis; rates of glycogen synthesis and degradation were 0.54 ± 0.16 and 2.12 ± 0.14 μmol ⋅ min-1 ⋅ g dry wt-1, respectively. During reperfusion (30 min), mechanical function recovered to 20% of preischemic values. Rates of synthesis and degradation were 1.66 ± 0.16 and 1.55 ± 0.21 μmol ⋅ min-1 ⋅ g dry wt-1, respectively, and glycogen content remained unchanged (25 ± 3 μmol/g dry wt). The assessment of glycogen metabolism needs to take into account the simultaneous synthesis and degradation of glycogen. With this approach, a substantial turnover of glycogen was detectable not only during aerobic conditions but also during ischemia as well as reperfusion.