AJP - Cell Physiology, Vol 262, Issue 6 C1507-C1512, Copyright © 1992 by American Physiological Society
Muscle fatigue in frog semitendinosus: role of intracellular pH
L. V. Thompson, E. M. Balog and R. H. Fitts
Biology Department, Marquette University, Milwaukee, Wisconsin 53233.
The purpose of this study was to utilize glass microelectrodes to
characterize the intracellular pH (pHi) before and during recovery from
fatigue in the frog semitendinosus (ST) muscle. A second objective was to
evaluate the relationship between pHi and contractile function. The frog ST
muscle (22 degrees C) was fatigued by direct electrical stimulation with
100-ms 150-Hz trains at 1/s for 5 min. Peak tetanic force (Po) was reduced
to 8.5% of initial force and recovered in a biphasic manner, returning to
the resting value by 40 min. Resting pHi was 7.00 +/- 0.02 (n = 37) and
declined with fatigue to an average value of 6.42 at 3 min of recovery.
During recovery pHi significantly increased and by 25 min had returned to
the prefatigue value. The pHi recovery was highly correlated to the slow
phase of Po recovery (r = 0.98, P less than 0.001). The mean resting
membrane potential was -78 +/- 1.0 mV (n = 42) and at 3 min of recovery was
depolarized to -67 +/- 4 mV. Both the peak rate of twitch force development
(+dP/dt) (r = 0.99, P less than 0.001) and decline (-dP/dt) (r = 0.94, P
less than 0.014) were highly correlated to pHi during the slow phase of
recovery. Contraction time (CT) and one-half relaxation time (1/2RT)
increased significantly and recovered exponentially. The recovery of CT and
1/2RT were both significantly correlated to pHi (r = -0.93, P less than
0.001 and r = -0.86, P less than 0.001 for CT and 1/2RT,
respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
