Linear dependence of muscle phosphocreatine kinetics on oxidative
capacity.
Paganini, Anthony T., Jeanne M. Foley, and Ronald A. Meyer.
Depts. of Physiology, Physical Education and Exercise Science and
Radiology, Michigan State University, East Lansing, MI48824
APStracts 3:0323C, 1996.
The influence of muscle oxidative capacity on phosphocreatine (PCr)
changes during and after stimulation was examined in the superficial
(fast-twitch) section of rat gastrocnemius muscles. Muscle
mitochondrial enzymes were increased in one group of rats by 8-10
weeks training on a running wheel (to a final regimen of 50 min/day
at 38 m/min, 5 days/week), and decreased in another group by chemical
thyroidectomy (0.025% methimazole [MMI] in drinking water for 8
weeks). After these treatments, muscle citrate synthase activity was
179% and 29% of that in corresponding control groups. Muscle PCr and
pH were measured by 31P-NMR spectroscopy before, during, and after 8
min of isometric twitch stimulation at 0.33 (MMI) or 0.75 Hz
(Trained), and 2 Hz. There was a significant linear correlation
(r=0.84, p<0.01) between the rate constant for PCr recovery
after submaximal stimulation (0.33 or 0.75 Hz) vs. citrate synthase
activity. Within the control groups, there was a significant
correlation (r=0.72, p<0.01) between the rate constant for PCr
recovery and intracellular pH at the end of stimulation. The results
are quantitatively consistent with linear/quasilinear models of
respiratory control by the cytoplasmic free energy of ATP hydrolysis,
but not with respiratory control by cytoplasmic ADP.
Received 1 March 1996; accepted in final form 30 August 1996.
APS Manuscript Number C117-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996