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.
Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kanoya, Japan.
T
T
Wakatsuki
Y
Y
Ohira
W
W
Yasui
K
K
Nakamura
T
T
Asakura
H
H
Ohno
M
M
Yamamoto
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