Kristensen Michael, Rasmussen Martin Krøyer, Juel Carsten
Copenhagen Muscle Research Centre, Department of Molecular Biology, University of Copenhagen, August Krogh building, Universitetsparken 13, 2100, Copenhagen Ø, Denmark.
Pflugers Arch. 2008 Aug;456(5):979-89. doi: 10.1007/s00424-008-0449-x. Epub 2008 Jan 24.
Muscle contraction may up-regulate the number of Na(+)-K(+) pumps in the plasma membrane by translocation of subunits. Since there is still controversy about where this translocation takes place from and if it takes place at all, the present study used different techniques to characterize the translocation. Electrical stimulation and biotin labeling of rat muscle revealed a 40% and 18% increase in the amounts of the Na(+)-K(+) pump alpha(2) subunit and caveolin-3 (Cav-3), respectively, in the sarcolemma. Exercise induced a 36% and 19% increase in the relative amounts of the alpha(2) subunit and Cav-3, respectively, in an outer-membrane-enriched fraction and a 41% and 17% increase, respectively, in sarcolemma giant vesicles. The Na(+)-K(+) pump activity measured with the 3-O-MFPase assay was increased by 37% in giant vesicles from exercised rats. Immunoprecipitation with Cav-3 antibody showed that 17%, 11% and 14% of the alpha(1) subunits were associated with Cav-3 in soleus, extensor digitorum longus, and mixed muscles, respectively. For the alpha(2), the corresponding values were 17%, 5% and 16%. In conclusion; muscle contraction induces translocation of the alpha subunits, which is suggested to be caused partly by structural changes in caveolae and partly by translocation from an intracellular pool.
肌肉收缩可能通过亚基的移位上调质膜中钠钾泵的数量。由于关于这种移位发生的起始位置以及是否真的发生仍存在争议，本研究采用了不同技术来表征这种移位。对大鼠肌肉进行电刺激和生物素标记显示，肌膜中钠钾泵α2亚基和小窝蛋白-3（Cav-3）的量分别增加了40%和18%。运动导致在外膜富集组分中α2亚基和Cav-3的相对量分别增加36%和19%，在肌膜巨囊泡中分别增加41%和17%。用3-O-甲基荧光素磷酸酶测定法测得的运动大鼠巨囊泡中的钠钾泵活性增加了37%。用Cav-3抗体进行免疫沉淀显示，在比目鱼肌、趾长伸肌和混合肌中，分别有17%、11%和14%的α1亚基与Cav-3相关联。对于α2亚基，相应的值分别为17%、5%和16%。总之，肌肉收缩诱导α亚基的移位，这被认为部分是由小窝的结构变化引起，部分是由从细胞内池的移位引起。
