Simultaneous determination of high energy phosphates and tension
production in an in vivo preparation of rabbit tibialis anterior
-extensor digitorum longus muscles.
Ryschon, T. W., J. C. Jarvis, S. Salmons, and R. S. Balaban.
Laboratory of Cardiac Energetics, National Heart, Lung and Blood
Institute, Bethesda, MD 20892 and Department of Human Anatomy and
Cell Biology, University of Liverpool, Liverpool, U.K.
APStracts 3:0555A, 1996.
The effects of repetitive muscle contraction on energy state and
tension production were studied in rabbit tibialis anterior/extensor
digitorum longus muscles that had been subjected to 90 days of
continuous indirect electrical stimulation at 10 Hz. Anesthetized
chronically stimulated and control rabbits were challenged with 15
min of stimulation at 4 and 15 tetani x min-1. Pi/PCr was measured in
vivo before, during and after acute stimulation by 31P-magnetic
resonance spectroscopy, and tension was recorded at the same time.
Although Pi/PCr was low at rest, it was significantly higher in
chronically stimulated muscle than in control muscle (0.20+/-0.02 vs.
0.05+/-0.01, p<0.05). Stimulation of control muscle for 15
minutes at both 4 and 15 tetani x min-1 induced a significant rise in
Pi/PCr, whereas the same conditions in chronically stimulated muscle
did not produce any significant departure from initial levels. The
tension produced by control muscle fell to 93+/-3% of its initial
value during stimulation at 4 tetani x min-1 and to 61+/-7% at 15
tetani x min-1. In chronically stimulated muscle, on the other hand,
tension was potentiated above its initial level at both stimulation
rates (135+/-15% and 138+/-11%, respectively), and remained
significantly elevated throughout each trial. The ability of
chronically stimulated muscle to sustain high levels of activity with
minimal perturbations in Pi/PCr or decrement in tension is
attributable to cellular adaptations that include a well-documented
increase in oxidative capacity.
Received 14 August 1995; accepted in final form 6 September 1996.
APS Manuscript Number A892-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996