The influence of mechanical loading upon myosin heavy chain protein
and mrna isoform expression.
Caiozzo, Vincent J., Fadia Haddad, Michael J. Baker, and Kenneth M.
Baldwin.
Departments of Orthopaedics and Physiology and Biophysics, College
of Medicine, University of California, Irvine, CA 92717
APStracts 2:0546A, 1995.
The overall objective of the studies reported herein was to examine
the effects of high resistance training upon MHC protein and mRNA
isoform expression. The findings from these studies can be summarized
as follows: i) there was a substantial increase in the fast Type IIX
MHC protein isoform content of the trained red and white MG muscles,
but this did not occur until after the 8th training session (i.e. 16
days); ii) single fiber analyses demonstrated that many so-called
fast Type IIB fibers contained small amounts of the fast Type IIX MHC
protein isoform, and that the high resistance training program
altered the bias of fast Type IIB:Type IIX MHC protein isoform
distribution in these fibers but did not increase the number of
fibers that could be categorized as exclusively fast Type IIX fibers;
iii) the high resistance training program produced a rapid (i.e.,
after 2 training sessions) elevation in the fast Type IIX MHC mRNA
isoform and a corresponding repression of the fast Type IIB MHC mRNA
isoform; and iv) the dose-response study revealed that as few as 10
contractions (40 s) per training session were capable of elevating
the expression of the fast Type IIX MHC mRNA isoform by approximately
250%. These collective findings demonstrate that high resistance
training is a powerful modulator of MHC protein isoforms and that
pretranslational mechanisms are very sensitive to even small amounts
of high resistance training.
Received 15 March 1995; accepted in final form 5 December 1995.
APS Manuscript Number A283-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95