Goodwin G W, Ahmad F, Taegtmeyer H
The University of Texas Houston Medical School, Department of Internal Medicine, Texas 77030, USA.
J Clin Invest. 1996 Mar 15;97(6):1409-16. doi: 10.1172/JCI118561.
We tested the hypothesis that glycogen is preferentially oxidized in isolated working rat heart. This was accomplished by measuring the proportion of glycolytic flux (oxidation plus lactate production) specifically from glycogen which is metabolized to lactate, and comparing it to the same proportion determined concurrently from exogenous glucose during stimulation with epinephrine. After prelabeling of glycogen with either 14C or 3H, a dual isotope technique was used to simultaneously trace the disposition of glycogen and exogenous glucose between oxidative and non-oxidative pathways. Immediately after the addition of epinephrine (1 microM), 40-50% of flux from glucose was directed towards lactate. Glycogen, however, did not contribute to lactate, being almost entirely oxidized. Further, glycogen utilization responded promptly to the abrupt increase in contractile performance with epinephrine, during the lag in stimulation of utilization of exogenous glucose, suggesting that glycogen serves as substrate reservoir to buffer rapid increases in demand. Preferential oxidation of glycogen may serve to ensure efficient generation of ATP from a limited supply of endogenous substrate, or as a mechanism to limit lactate accumulation during rapid glycogenolysis.
我们验证了糖原在离体工作的大鼠心脏中优先被氧化的假说。这是通过测量糖酵解通量（氧化加乳酸生成）中专门来自糖原并代谢为乳酸的比例，并将其与在肾上腺素刺激期间同时从外源性葡萄糖测定的相同比例进行比较来实现的。在用(^{14}C)或(^{3}H)对糖原进行预标记后，采用双同位素技术同时追踪糖原和外源性葡萄糖在氧化和非氧化途径之间的去向。加入肾上腺素（(1)微摩尔）后立即发现，来自葡萄糖的通量有(40 - 50%)流向乳酸。然而，糖原并不生成乳酸，几乎完全被氧化。此外，在刺激外源性葡萄糖利用出现延迟期间，糖原利用对肾上腺素引起的收缩性能突然增加迅速做出反应，这表明糖原作为底物储备来缓冲需求的快速增加。糖原的优先氧化可能有助于确保从有限的内源性底物供应中高效生成ATP，或者作为一种在快速糖原分解过程中限制乳酸积累的机制。
