LOL. Is this all I am to you guys - some sort of automated, walking, talking dictionary?...
Never mind... ;^)
Basically, the used mouse and cow muscle cells that were not fully developed (but doing so, and growing in size in a culture dish), to see how interleukin-15 affects development and growth. IL-15 is a cytokine, or type of cell-to-cell communication molecule that skeletal muscle cells (among others) use to communicate, *presumably* when adapting to an exercise stimulus (GROW, BABY!).
The IL-15 didn't affect the rate of proliferation or doubling of the developing cells (thymidine incorporation), which I would presume means it would not necessarily affect satellite cell division, which is necessary for muscle cells to grow (more on this if you want). However, it did increase the rate of myosin heavy chain accumulation, the major contractile protein. The cells were bigger with more contractile protein!
To compare it to IGF-1 (and eliminate the effect of IGF-1 on cell doubling), they blocked cellular proliferation (making new cells) with a chemical and found that in the cow cells, IL-15 and IGF-1 each doubled contractile protein production alone. Cool thing is, the effect was ADDITIVE when BOTH IGF-1 and IL-15 were both in the cell medium: the IGF-1 and IL-15 were acting via different pathways.
Bottom line. IL-15 increased muscle cell growth, but *might* not have the effect on satellite cells necessary for muscle cell growth (more on this, if you're interested). IL-15 and IGF-1 seem to increase cell size via different mechanisms. (Sounds like a recipe for a stack!!! LOL)
Limitations (among others):
These were developing cell lines. I have seen similar data using nearly the same model (fetal mouse muscle cells) showing that creatine was just as anabolic. We know it don't work THAT good (if at all!).
A developing muscle cell (not yet fully differentiated or even innervated!) is a hell of a lot different than a mature one in a functioning body.
Is IL-15 increased in response to an exercise stimulus?...
Where is the control group?... Were they simply *restoring* normal muscle contractile prot. accumulation by putting some IL-15 there?... (What are in utero levels?...). This is a problem with these kinds of in vitro (culture dish, etc.) studies. An analogy would be if you compared *no* protein consumption versus RDA protein consumption on gains in muscle mass with resistance training. Duh.
All of the issues of comparing the culture medium with that in vivo, e.g., concentration of the IL-15, half-life, feedback inhibition of its production, etc.
These were not human cells.
Hope this helps, man.
-Randy
