Contractile characteristics of skeletal muscles depleted of phosphocreatine
Petrofsky, J.S.; Fitch, C.D.
Pflugers Archiv European Journal of Physiology 384(2): 123-129
1980
ISSN/ISBN: 0031-6768 PMID: 7189875 Document Number: 154900
The contractile characteristics of skeletal muscle were evaluated after phosphocreatine depletion was accomplished by feeding weanling female rats a ground chow diet containing 1% of .beta.-guanidinopropionic acid for 10 wk. Except for a slight decrease in initial strength and a 30% decrease in wet weight, phosphocreatine depleted plantaris muscles exhibited no abnormalities. Phosphocreatine depleted soleus muscles exhibited several significant abnormalities. In an isometric twitch, the rise time was prolonged from 57 .+-. 6 ms (mean .+-. SD) for 6 control rats to 87 .+-. 6 for 6 phosphocreatine depleted rats, the amplitude was decreased from 264 .+-. 11 g/g wet weight of muscle to 163 .+-. 9, and the half-relaxation time was prolonged from 61 .+-. 6 ms to 85 .+-. 8. The maximum velocity of shortening was also reduced from 3 to 2 muscle lengths per second, the maximum isometric tension was reached at a lower frequency of synchronous stimulation (30 vs. 50 Hz), the initial strength was reduced from 1065 .+-. 76 g/g wet weight of muscle to 752 .+-. 69, and the isometric endurance was increased from 340 .+-. 16 s to 973 .+-. 95. The molecular basis for these effects of phosphocreatine depletion on the contractile characteristics of soleus muscles remains to be elucidated.