Skeletal muscle myosin heavy chain synthesis rate in healthy
humans.
Balagopal, P., O. Ljungqvist, and K. S. Nair.
Endocrine Research Division, Mayo Clinic and Foundation, Rochester,
MN -55905 and Department of Medicine, University of Vermont,
Burlington, VT-05405
APStracts 3:0173E, 1996.
Mixed muscle protein synthetic rate has been measured in humans. These
measurements represent the average of synthetic rates of all muscle
proteins with variable rates. We determined to what extend the
synthesis rate of mixed muscle protein in humans reflects that of
myosin heavy chain (MHC), the main contractile protein responsible
for the conversion of adenosine triphosphate to mechanical energy as
muscle contraction. Fractional synthetic rates of MHC and mixed
muscle protein were measured from the increment of [13C]leucine in
these proteins in vastus lateralis biopsy samples taken at 5h and 10h
during a primed continuous infusion of L-[1-13C]leucine in ten young
healthy subjects. Calculations were done using plasma
[13C]ketoisocaproate (KIC) and muscle tissue fluid [13C]leucine] (TF)
as surrogate measures of leucyl-tRNA. Fractional synthetic rate of
MHC using plasma KIC (0.0299+/-0.0043%/h) and TF leucine (0.0443+/
-0.0056%/h) were only 72 +/- 3 % of that of mixed muscle protein
(0.0408+/-0.0032%/h and 0.0603+/- 0.0059%/h respectively using KIC
and TF). Contribution of MHC (7+/-1 mg/kg/h) to synthetic rates of
whole body mixed muscle protein (36+/-5 mg/kg/h) and whole body
protein (127+/-4 mg/kg/h) is only 18+/-1% and 5+/-1% respectively.
This relatively low contribution of MHC to whole body and mixed
muscle protein synthesis warrants direct measurement of synthesis
rate of MHC in conditions involving abnormalities of muscle
contractile function.
Received 7 June 1996; accepted in final form 13 August 1996.
APS Manuscript Number E283-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996