47
and recovery was observed. Dantrolene sodium, dissolved
in propylene glycol (25 mg/ml) was injected I.V. during
contractions at 0.2/sec. Dantrolene impairs release
of Ca from the lateral sacs (24). This is accomplished
without changes in the action potential and is apparently
a direct effect on the lateral sacs. Sufficient drug
was given to reduce AT at least 50% (2-5 mg/kg). To
study the effects of reducing the number of motor units
contracting, the stimulation voltage was reduced while
the muscle contracted 0.2/sec. This results in excitation
of fewer motor neurons and their motor units. Consequently
less tension is developed. Comparing the twitch
characteristics of a normal versus a fatigued muscle may
provide information leading to an understanding of the
mechanism(s) of fatigue.
Also, in a few experiments, samples of muscles were
obtained immediately following the 30 minute stimulation
period, and/or after 40 minutes of recovery. Samples
were frozen in situ with metal clamps pre-cooled in
liquid nitrogen. Small samples (30-80 mg) were then
homogenized (Vertis homogenizer) in perchloric acid
(.8% in 40% ethanol) and analyzed for phosphorylcreatine
by the method of Ennor and Stocken (25) (see Appendix).
Statistical analysis was by the two way analysis of
variance for repeated measures. Differences between means
were determined by Duncan's multiple range test (2).