Responses of contractile properties in rat soleus to high-energy phosphates and/or unloading.
Responses of contractile properties of soleus to unloading and/or changes in high-energy phosphate contents were studied in rats. Reduction of high-energy phosphates, especially phosphocreatine, in ankle extensors was induced by feeding beta-guanidinopropionic acid (beta-GPA). The major finding in the study was that the fatigability and speed-related contractile properties responded to unloading and creatine supplementation in a similar manner. The high-energy phosphate contents tended to be elevated after 10-d supplementation of creatine and hindlimb suspension. The shift toward slow-type, mainly due to an increased one-half relaxation time, was seen in rats fed beta-GPA. Such a shift was reversed by feeding creatine or by hindlimb suspension; however, the suspension-induced shift of contractile properties toward fast-type was not prevented completely by beta-GPA feeding. Although the muscle fatigue resistance did not change by beta-GPA feeding alone, the decrease in fatigue resistance following suspension and creatine supply was less in the beta-GPA group. It is suggested that the levels of high-energy phosphates and tension production play important roles in the regulation of contractile properties of the soleus muscle.
Wakatsuki
T
T
Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kanoya, Japan.
Ohira
Y
Y
Yasui
W
W
Nakamura
K
K
Asakura
T
T
Ohno
H
H
Yamamoto
M
M
D000818:Animals; D004558:Electric Stimulation; D004734:Energy Metabolism; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects*; D010710:Phosphates / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D014893:Weightlessness
D010710:Phosphates