The role of excitation-contraction coupling in skeletal muscle
fatigue  Edward Michael Balog, Marquette University   The
effects of fatigue on excitation-contraction coupling (ECC) in
frog skeletal muscle was examined using conventional and ion-
selective microelectrodes, and the vaseline gap method of
voltage clamping. As a result of stimulation (100 ms trains at
150 Hz, 1/sec for 5 min), the resting membrane potential (RMP)
depolarized 9 mV, the action potential (AP) overshoot (OS) fell
12 mV, the duration of the AP was prolonged 2 fold, the
intracellular Na$\sp+$ concentration rose from 16 to 50 mM while
intracellular K$\sp+$ fell from 141 to 100 mM. The RMP and OS
recovered by 2 min and the intracellular ions by 5 min, at which
time the duration was still prolonged. In addition, as fatigue
developed, the membrane failed to respond to each stimulus with
an AP. In the worse case, the muscle responded to 15 stimuli
with only 3 APs. Since a 9 mV depolarization of the RMP would
not inactivate a significant perc