Bhandari A, Xia Y, Cortright R, Dohm G L, Bazzy A R
Department of Pediatrics, Yale University School of Medicine, New Haven, CT 06510, USA.
Med Sci Sports Exerc. 2000 Aug;32(8):1406-11. doi: 10.1097/00005768-200008000-00008.
Endurance exercise training is associated with enhanced glucose uptake and hence improvement in carbohydrate metabolism. Glucose transport (GLUT) membrane proteins are regulated by a variety of physiological stimuli, including exercise. In limb muscle, both acute exercise and endurance training enhance the expression of the skeletal muscle transporter, GLUT-4. The purpose of this study is to determine whether chronic loading enhances GLUT-4 expression in the diaphragm.
The effect of chronic inspiratory flow resistive (IFR) loading on diaphragm GLUT-4 was studied in a model of respiratory muscle endurance training in sheep. IFR loads (resistance 50-100 cm H2O x L(-1) x s(-1)) were maintained for 3 h x d(-1), 5-6 d x wk(-1) for 3 wk. Loading was adjusted so that PaO2 was >60 Torr and PaCO2 <45 Torr in room air. Six untrained sheep were used as controls. GLUT-4 protein and mRNA were analyzed by Western and Northern analysis respectively.
GLUT-4 protein levels were two-fold greater in trained animals when compared with controls (P < 0.01). GLUT-4 mRNA levels in the trained muscles was not significantly different from controls.
We conclude that in the sheep diaphragm, chronic IFR loading increases GLUT-4 protein levels. This increase may be one of the mechanisms contributing to the improved respiratory muscle endurance previously demonstrated in this animal model of respiratory muscle training.
耐力运动训练与葡萄糖摄取增加相关，从而改善碳水化合物代谢。葡萄糖转运（GLUT）膜蛋白受多种生理刺激调节，包括运动。在肢体肌肉中，急性运动和耐力训练均可增强骨骼肌转运体GLUT-4的表达。本研究的目的是确定慢性负荷是否会增强膈肌中GLUT-4的表达。
在绵羊呼吸肌耐力训练模型中，研究慢性吸气气流阻力（IFR）负荷对膈肌GLUT-4的影响。IFR负荷（阻力50 - 100 cm H2O×L⁻¹×s⁻¹）维持3小时/天，5 - 6天/周，持续3周。调整负荷以使室内空气中的动脉血氧分压（PaO2）>60 Torr且动脉血二氧化碳分压（PaCO2）<45 Torr。六只未经训练的绵羊用作对照。分别通过蛋白质免疫印迹法和Northern印迹法分析GLUT-4蛋白和mRNA。
与对照组相比，训练动物的GLUT-4蛋白水平高出两倍（P < 0.01）。训练肌肉中的GLUT-4 mRNA水平与对照组无显著差异。
我们得出结论，在绵羊膈肌中，慢性IFR负荷会增加GLUT-4蛋白水平。这种增加可能是导致先前在该呼吸肌训练动物模型中所证明的呼吸肌耐力改善的机制之一。
