Acidosis has no effect on the atp cost of contraction in cat fast-
and slow-twitch skeletal muscles.
Harkema, Susan J., Gregory R. Adams, and Ronald A. Meyer.
Depts. of Physiology and Radiology, Michigan State University, East
Lansing, Michigan 48824
APStracts 3:0281C, 1996.
Studies of skinned fibers suggest that the rate of ATP turnover in
skeletal muscle is depressed by acidosis. In order to examine if this
occurs in intact muscles, the ATP cost of isometric contractions was
measured in ex vivo, arterially-perfused cat biceps (predominantly
fast-twitch) and soleus (slow-twitch) muscles under normocapnic
(5%CO2) and hypercapnic (70%CO2) conditions. Hypercapnia decreased
extracellular pH from 7.4 to 6.7, and intracellular pH from 7.1 to
6.5 (soleus) or 6.6 (biceps), but had no significant effect on the
PCr/ATP ratio in muscles at rest. The ATP cost of contraction was
estimated from PCr changes, measured by gating the acquisition of
31P-NMR spectra to times before and after brief tetani (1s@100Hz and
2s@25Hz for biceps and soleus, respectively) or 10 s trains of
twitches (2 and 1 Hz, respectively). Peak isometric force and the ATP
cost of tetanic contraction (PCr/ force*time integral) were not
significantly different under hypercapnic compared to normocapnic
conditions in either muscle (mean: 7.97 and 2.44 [mu]mole * (kg*s)-1
for biceps and soleus, respectively). Twitch force and the ATP cost
per twitch decreased by nearly 50% during hypercapnic perfusion in
both muscle types. The results indicate that hypercapnic acidosis has
no significant effect on the ATPase rate per active myosin head in
intact mammalian skeletal muscle.
Received 1 March 1996; accepted in final form 30 August 1996.
APS Manuscript Number C115-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996