Orginal Publication Date
MCV/Q, Medical College of Virginia Quarterly
On the basis of the clear-cut differentiation used in fast (twitch) and slow (tonic) muscles of the frog, both the fast E.D.L. and the slow soleus muscle should be considered twitch muscles. However, they reveal a marked differential behavior in their contracture responses to ACh and caffeine. Moreover, all the slow muscles I have studied (i.e.. the L.D.A. of the chicken, the rectus abdominis of the frog, and the soleus of the rat) show a higher rate of proteosynthesis. This may be related to the basic function of slow muscles concerned with long-lasting maintenance of tension, the extreme being, for example, the contracture responses observed in reaction to ACh. There may be a relation of rate of protein metabolism to the mobility of protein-bound Ca⁺⁺ in the sarcoplasmatic reticulum. The differences in contracture behavior are apparent already three days after birth of the animals. All this may indicate a basic differentiation of two main groups of muscle fibers. Neural long-term influences operate in the development of this differentiation in contracture behavior of fast and slow muscle fibers. The mechanisms by which the nerve cell affects this behavior have still to be uncovered.
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