Carnitine metabolism in human muscle fiber types during submaximal
dynamic exercise.
Constantin-Teodosiu, D., S. Howell, and P. L. Greenhaff.
Queen's Medical Center, Department of Physiology and Pharmacology,
University Medical School, Nottingham NG7 2UH, United Kingdom
APStracts 3:0008A, 1996.
The effect of prolonged exhaustive exercise on free- and
acetylcarnitine concentrations in mixed-fibered skeletal muscle and
in type I and II muscle fibers was investigated in man. Needle biopsy
samples were obtained from the vastus lateralis of six subjects
immediately after exhaustive one-legged cycling at 75% of VO2 max
from both the exercised and non-exercised (control) legs. In the
resting (control) leg, there was no difference in the free carnitine
concentration between type I and II fibers (20.36+/-1.25 and 20.51+/
-1.16 mmol/kg dm, respectively), despite the greater potential for fat
oxidation in type I fibers. However, the acetylcarnitine
concentration was slightly greater in type I fibers (P<0.01).
During exercise, acetylcarnitine accumulation occurred in both muscle
fiber types but accumulation was greatest in type I fibers
(P<0.005). Correspondingly, the concentration of free carnitine
was significantly lower in type I fibers at the end of exercise
(P<0.001). The sum of free- and acetylcarnitine concentrations
in type I and II fibers at rest were similar and were unchanged by
exercise. In conclusion, the findings of the present study support
the suggestion that carnitine buffers excess acetyl group formation
during exercise and that this occurs in both type I and II fibers.
However, the greater accumulation of acetylcarnitine in type I during
prolonged exercise probably reflects the greater mitochondrial
content of this fiber type.
Received 20 June 1995; accepted in final form 1 December 1995.
APS Manuscript Number A657-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96