Juel Carsten
Dept. of Biology, Univ. of Copenhagen, August Krogh Bldg., Universitetsparken 13, DK-2100 Copenhagen, Denmark.
Am J Physiol Regul Integr Comp Physiol. 2009 Jan;296(1):R125-32. doi: 10.1152/ajpregu.90760.2008. Epub 2008 Nov 5.
It is unclear whether muscle activity reduces or increases Na(+)-K(+)-ATPase maximal in vitro activity in rat skeletal muscle, and it is not known whether muscle activity changes the Na(+)-K(+)-ATPase ion affinity. The present study uses quantification of ATP hydrolysis to characterize muscle fiber type-specific changes in Na(+)-K(+)-ATPase activity in sarcolemmal membranes and in total membranes obtained from control rats and after 30 min of treadmill running. ATPase activity was measured at Na(+) concentrations of 0-80 mM and K(+) concentrations of 0-10 mM. K(m) and V(max) values were obtained from a Hill plot. K(m) for Na(+) was higher (lower affinity) in total membranes of glycolytic muscle (extensor digitorum longus and white vastus lateralis), when compared with oxidative muscle (red gastrocnemius and soleus). Treadmill running induced a significant decrease in K(m) for Na(+) in total membranes of glycolytic muscle, which abolished the fiber-type difference in Na(+) affinity. K(m) for K(+) (in the presence of Na(+)) was not influenced by running. Running only increased the maximal in vitro activity (V(max)) in total membranes from soleus, whereas V(max) remained constant in the three other muscles tested. In conclusion, muscle activity induces fiber type-specific changes both in Na(+) affinity and maximal in vitro activity of the Na(+)-K(+)-ATPase. The underlying mechanisms may involve translocation of subunits and increased association between PLM units and the alphabeta complex. The changes in Na(+)-K(+)-ATPase ion affinity are expected to influence muscle ion balance during muscle contraction.
目前尚不清楚肌肉活动会降低还是增加大鼠骨骼肌中钠钾ATP酶的最大体外活性，也不清楚肌肉活动是否会改变钠钾ATP酶的离子亲和力。本研究采用ATP水解定量法，以表征对照组大鼠以及跑步机跑步30分钟后的大鼠肌膜和总膜中钠钾ATP酶活性的肌纤维类型特异性变化。在0-80 mM的Na(+)浓度和0-10 mM的K(+)浓度下测量ATP酶活性。通过希尔图获得米氏常数（K(m)）和最大反应速度（V(max)）值。与氧化型肌肉（红色腓肠肌和比目鱼肌）相比，糖酵解型肌肉（趾长伸肌和白色股外侧肌）的总膜中Na(+)的K(m)值更高（亲和力更低）。跑步机跑步导致糖酵解型肌肉总膜中Na(+)的K(m)显著降低，这消除了Na(+)亲和力的纤维类型差异。K(+)的K(m)（在存在Na(+)的情况下）不受跑步影响。跑步仅增加了比目鱼肌总膜中的最大体外活性（V(max)），而在其他三种测试肌肉中V(max)保持不变。总之，肌肉活动会诱导钠钾ATP酶的Na(+)亲和力和最大体外活性发生纤维类型特异性变化。潜在机制可能涉及亚基的易位以及PLM单元与αβ复合物之间关联的增加。钠钾ATP酶离子亲和力的变化预计会影响肌肉收缩期间的肌肉离子平衡。
