Relationship between the contents of high-energy phosphates and Regulation of muscular properties

众所周知，骨骼肌的特性受运动训练、环境、营养、生长发育和/或衰老的影响。肌肉收缩的能量来源是三磷酸腺苷，它是通过有氧和无氧能量代谢合成的。它还受肌酸含量的影响(AJP Cell Physiol，‘94；JPn J Physiol，’94&‘95)。然而，调节肌肉收缩和代谢特性的确切机制仍不清楚。因此，本研究通过饲喂肌酸类似物β-GPA(β-GPA)来研究肌酸耗竭对C57BL6小鼠足底肌电特性的影响。将3周龄雄性小鼠随机分为两组。一组小鼠饲喂常规粉末状饲料，另一组饲喂相同的饲料，但添加1%的β-GPA。随着生长发育，配对喂养的食量逐渐增加，但在3周后，每只小鼠每天摄入1g食物。水是临时供应的。分别于第4周和第8周取血和肌肉标本。在静脉注射麻醉下从颈静脉取血。注射戊巴比妥钠。离心后保存血清，测定肌酸含量。分别于双侧足底肌取标本。对右肌横断面的肌纤维类型进行分析。测定左侧肌肉中的基因表达。特别是在β-GPA喂养8周后，肌酸显著减少，纤维向慢型转变。慢型纤维和线粒体代谢相关基因的表达在第4周仍有增加。提示肌酸耗竭导致肌纤维向慢抽动型转化。

It is known that the properties of skeletal muscles are regulated in response to exercise training, environment, nutrition, growth and development, and/or aging. The energy source for muscle contraction is adenosine triphosphate (ATP), which is synthesized through aerobic and anaerobic energy metabolism. It is also influenced by the content of creatine (AJP Cell Physiol, ’94; Jpn J Physiol, ’94 & ’95). However, the precise mechanism responsible for the regulation of contractile and metabolic properties of muscles is still unclear. Therefore, the current study was performed to investigate the effects of creatine depletion, by feeding creatine analogue, β-guanidinopropionic acid (β-GPA) on the properties of plantaris muscle of C57BL6 mice. Three weeks old male mice were separated into two groups randomly. One group of mice were fed regular powdered diet and other group were supplied the same diet, but containing 1% β-GPA. The amount of food, pair -fed, was gradually increased following growth, but 1 g of food was given to each mouse daily after 3 weeks. Water was supplied ad libitum. At 4th and 8th week, blood and muscle samplings were performed. Blood was withdrawn from the jugular vein under anesthesia with i.p. injection of sodium pentobarbital. Serum was saved after centrifugation and creatine content was analyzed. Plantaris muscles were sampled bilaterally. Muscle fiber types were analyzed in the cross-section of right muscles. Gene expressions were determined in the left muscles. Significant depletion of creatine and shift of fibers toward slow-type were noted, especially after 8 weeks of β-GPA feeding. Increase in the expression of genes related to slow-type fibers and mitochondrial metabolism was noted even at 4th week. It is suggested that depletion of creatine causes the transformation of muscle fibers toward slow-twitch type.