Merrill G F, Florini J R, Dulak N C
J Cell Physiol. 1977 Nov;93(2):173-82. doi: 10.1002/jcp.1040930202.
The effects of a somatomedian analog, Temin's multiplication stimulating activity (MSA), on amino acid transport into muscle cells have been characterized in a series of experiments on myoblasts and myotubes in culture. Addition of MSA to serum-starved L6 myoblasts increased the rate of aminoisobutyrate (AIB) uptake 50-150% within five hours. This early effect on transport was followed by increases in cell number, protein content and 3H-thymidine incorporation. Kinetic analyses indicated that MSA increased the maximal velocity of AIB uptake but had no effect on the KM for AIB. When myoblasts were allowed to fuse (and dividing cells eliminated by addition of 10(-4) M cytosine arabinoside) the AIB transport system(s) remained similarly responsive to MSA. In myoblasts and in myotubes, both the basal and MSA-stimulated rate of AIB uptake were sodium-dependent processes; little stimrulation occurred if sodium was absent from the labeling medium. Further suggesting the involvement of cations in response to hormone, MSA stimulated uptake of the potassium analog, 86Rb+, and increase net intracellular potassium in both myoblasts and myotubes. MSA was active at concentrations equivalent to in vivo levels of somatomedins; neither insulin nor growth hormone had any effect at or near physiological concentrations.
在一系列针对培养的成肌细胞和肌管的实验中，已对生长调节素类似物——特明氏增殖刺激活性物质（MSA）对氨基酸转运进入肌肉细胞的作用进行了表征。向血清饥饿的L6成肌细胞中添加MSA，在五小时内使氨基异丁酸（AIB）摄取速率提高了50 - 150%。这种对转运的早期作用之后是细胞数量、蛋白质含量和³H - 胸腺嘧啶核苷掺入量的增加。动力学分析表明，MSA提高了AIB摄取的最大速度，但对AIB的米氏常数（KM）没有影响。当成肌细胞被允许融合（并通过添加10⁻⁴M阿糖胞苷消除分裂细胞）时，AIB转运系统对MSA仍保持类似的反应性。在成肌细胞和肌管中，AIB摄取的基础速率和MSA刺激的速率都是钠依赖性过程；如果标记培养基中没有钠，则几乎没有刺激作用。进一步表明阳离子参与对激素的反应，MSA刺激钾类似物⁸⁶Rb⁺的摄取，并增加成肌细胞和肌管中的细胞内钾净含量。MSA在相当于体内生长调节素水平的浓度下具有活性；胰岛素和生长激素在生理浓度或接近生理浓度时均无任何作用。
