Noninvasive measurement of phosphocreatine recovery kinetics in
single human muscles.
Walter, Glenn, Krista Vandenborne, Kevin K. McCully[acute]a, and John
S. Leigh.
Department of Biochemistry and Biophysics, Department of Radiology,
Department of Rehabilitation Medicine, University of
Pennsylvania,Department of Medicine, Medical College of Pennsylvania,
Philadelphia, PA
APStracts 3:0310C, 1996.
The rate at which phosphocreatine (PCr) is resynthesized following
exercise is related to muscle oxidative capacity (Vmax). Using a 1
-dimensional image guided, localized Nuclear Magnetic Resonance
Spectroscopy technique PCr kinetics were monitored in the medial
gastrocnemius of eight healthy subjects following voluntary, short
duration, maximal rate exercise (MAX). Localized spectra were
obtained every 6s with less than 5% contamination from nonselected
regions. MAX exercise elicited near-maximal to maximal muscle
activation as indicated by the high PCr hydrolysis rate (2.26 0.07
mM/s) and extensive PCr depletion. At the end of 9s of MAX exercise,
PCr was depleted by 61.4 2.4% and intracellular pH was 7.04 0.03.
Following 9S-MAX, PCr recovered with a rate constant (kPCr) of 1.87
0.15 min-1, and a Vmax of 67.2 6.0 mM/min. Independent of prior
activity, aerobic ATP synthesis rates reached 48.6 4.9 mM/min within
9s. Extending MAX exercise to 30s, resulted in 92.0 1.2% PCr
depletion and an intracellular pH of 6.45 0.07. The intracellular
acidosis separated the direct relationship between kPCr and muscle
oxidative capacity, but did not affect the initial PCr resynthesis
rate.
Received 23 October 1995; accepted in final form 27 September
1996.
APS Manuscript Number C646-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996