SUBSTRATE REGULATION BY SKELETAL MUSCLE AFTER HINDLIMB SUSPENSION

在太空旅行中，伸展肢体的卸载可能会减少 职能能力，如使命的安全和效力， 暴露了 肢体卸载的后肢悬吊模型改变了 骨骼肌的生化和收缩特性 导致肌纤维萎缩和I型向II型转化。 在 相反，运动训练会引起生物化学的改变， 但不是收缩性的，骨骼肌的特征，主要是 在运动过程中增加使用脂肪作为底物的能力。 的 本项目的实验将区分 内在肌纤维类型转换的后果和 生化适应正常的运动训练。 初步 在大鼠中进行实验， 休息、运动和运动期间的[3- 13 C]乳酸和[1，2 - 13 C]乙酸 运动后糖原耗尽。 我们发现， 腓肠肌（II型肌肉），将[3- 13 C]乳酸盐掺入 TCA循环从15.7%增加到静息时的24.8%和45.9%， 在对照运动后，以及在糖原耗尽的运动后。 同时，[1，2 - 13 C]乙酸酯的掺入从 54.4%至39.7%和30.9%。 TCA循环的回补是 与锻炼时间成正比。 相反，比目鱼肌（I型） 肌肉）吸收了更大部分的[1，2 - 13 C]乙酸盐， [3- 13 C]乳酸的分数，没有检测到TCA循环回补。 比目鱼肌和腓肠肌之间的巨大差异 提供了一个敏感的指标的代谢后果的任何 后肢悬吊引起的纤维类型转换， 运动训练对部分减弱 纤维类型转换 （服务7）报告期： (09（1997年1月至1998年8月31日）

The extended limb unloading during space travel may diminish functional capacity such that mission safety and effectiveness are compromised. The hindlimb suspension model of limb unloading alters both biochemical and contractile characteristics of skeletal muscle causing atrophy and type I to type II conversion of muscle fibers. In contrast, exercise training induces alterations in the biochemical, but not contractile, characteristics of skeletal muscle, primarily an increased capacity to use fat as a substrate during exercise. The experiments in this project will differentiate between the consequences of intrinsic muscle fiber type conversion and the biochemical adaptations to normal exercise training. Preliminary experiments were conducted in the rat using infusions of [3-13C]lactate and [1,2-13C]acetate during rest, exercise, and exercise following glycogen depletion. We found that in the gastrocnemius (a type II muscle), incorporation of [3-13C]lactate into the TCA cycle increased from 15.7% to 24.8% and 45.9% during rest, after control exercise, and after exercise with glycogen depletion. At the same time, incorporation of [1,2-13C]acetate declined from 54.4% to 39.7% and 30.9%. Anaplerosis of the TCA cycle was proportional to exercise time. In contrast, the soleus (a type I muscle) took up a greater fraction of [1,2-13C]acetate and a lower fraction of [3-13C]lactate, with no detectable TCA cycle anaplerosis. This great difference between the soleus and the gastrocnemius provides a sensitive indicator of the metabolic consequences of any fiber type conversions induced by hindlimb suspension, and the efficacy of exercise training to partially attenuate the effects of fiber type conversion. (Service 7) REPORT PERIOD: (09/01/97-08/31/98)