The Journal of General Physiology, Vol 75, 617-631, Copyright © 1980 by The Rockefeller University Press
Effects of previous activity on the energetics of activation in frog skeletal muscle
JA Rall
Effects of previous activity on the ability of frog skeletal muscle at 0
degrees C to liberate energy associated with contractile activation, i.e.,
activation heat (AH), have been examined. Earlier work suggests that
activation heat amplitude (as measured from muscles stretched to lengths
where active force development is nearly abolished) is related to the
amount of Ca2+ released upon stimulation. After a twitch, greater than 2 s
is required before a second stimulus (AHt) can liberate the same activation
heat as a first stimulus (AH infinity), i.e., (AHt)/(AH infinity) = 1 -0.83
e-1.40t, where t is time in seconds. Caffeine introduces a time delay in
the recovery of the ability to generate activation heat after a twitch.
After a tetanus, the activation heat is depressed to a greater extent at
any time than after a twitch. The activation heat elicited by a stimulus 1
s after a tetanus is depressed progressively with respect to tetanus
duration up to 3 s. For tetani of 3, 40, and 80 s duration the postetanus
activation heat is comparably depressed. The time-course of the recovery of
the ability of the muscle to produce activation heat after a tetanus can be
described as (AHt)/(AH infinity) = 1 -0.80 e-0.95t - 0.20 e-0.02t. Greater
than 90 s is required before the posttetanus activation heat is equal to
the pretetanus value. The faster phase of recovery is similar to recovery
after the twitch and the slower phase may be associated with the return of
calcium to the terminal cisternae from uptake sites in the longitudinal
sarcoplasmic reticulum.
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