Phosphagen and intracellular pH changes during contraction of creatine-depleted rat muscle.
Phosphagen and intracellular pH changes during contraction of creatine-depleted rat muscle.
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DOI：
10.1152/ajpcell.1986.250.2.c264
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发表时间：
1986-02
期刊：
影响因子：
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通讯作者：
R. Meyer;T. Brown;B. Krilowicz;M. Kushmerick
中科院分区：
文献类型：
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作者：
R. Meyer;T. Brown;B. Krilowicz;M. Kushmerick
为了评估磷酸肌酸（PCr）和肌酸在肌肉代谢中的功能作用，通过给大鼠喂食肌酸类似物β-胍基丙酸酯（β-GPA，2%的饮食）来消耗这些化合物。磷酸盐代谢产物和细胞内pH值的变化进行了监测，在腓肠肌原位磷核磁共振（31 P-NMR）在162 MHz，使用表面线圈技术。喂养3个月后，25 mumol/g的磷酸化beta-GPA（beta-GPAP）已经积累，PCr，肌酸和ATP水平分别降低到6，17和56%，与对照组动物的肌肉相比。在静息肌肉中，通过NMR饱和转移方法，β-GPAP和ATP之间没有可测量的磷酸盐交换。在1和5 Hz的肌肉刺激过程中，β-GPAP水解的最大净速率是对照肌肉中PCr的10%，因此在150 s后无机磷酸盐增加到低于对照肌肉中达到的水平的50%。在这两种速率下，峰值抽搐力在β-GPA负载的肌肉中更快地向稳定状态下降，但在100 s后，在β-GPA喂养的动物中，力没有差异（1 Hz）或显著更大（5 Hz）。与对照组相比，在刺激过程中细胞内pH值最初下降得更快，之后在β-GPA负载的肌肉中恢复得更快。这种差异可以通过净PCr水解引起的预期质子消耗的差异来解释。然而，尽管通过PCr水解进行缓冲，但pH最终在对照肌肉中降低更多（对于5 Hz为6.1对6.3），表明与β-GPA负载的肌肉相比更大的酸积累。在表面，主要是快速抽搐糖酵解部分的肌肉钳冷冻后，5赫兹刺激150秒，乳酸积累是对照组的两倍。结果表明，PCr是不是必不可少的稳态能量生产，但从PCr水解的磷酸盐可能是重要的糖原分解和/或糖酵解的最大激活。
To evaluate the functional role of phosphocreatine (PCr) and creatine in muscle metabolism, these compounds were depleted by feeding rats the creatine analogue, beta-guanidinopropionate (beta-GPA, 2% of diet). Changes in phosphate metabolites and intracellular pH were monitored in gastrocnemius muscle in situ by phosphorus nuclear magnetic resonance (31P-NMR) at 162 MHz using the surface coil technique. After 3 mo of feeding, 25 mumol/g of phosphorylated beta-GPA (beta-GPAP) had accumulated, and PCr, creatine, and ATP levels were reduced to 6, 17, and 56%, respectively, compared with muscles of control animals. In resting muscle, there was no measurable exchange of phosphate between beta-GPAP and ATP by the NMR saturation transfer method. During muscle stimulation at 1 and 5 Hz, the maximum net rate of beta-GPAP hydrolysis was 10% that of PCr in control muscles, so that after 150 s inorganic phosphate had increased to less than 50% of the level attained in control muscles. At both rates, peak twitch force declined toward a steady state more rapidly in beta-GPA-loaded muscles, but after 100 s force was either not different (1 Hz) or significantly greater (5 Hz) in the beta-GPA-fed animals. Intracellular pH initially decreased more rapidly during stimulation and recovered more rapidly afterward in the beta-GPA-loaded muscles compared with controls. This difference could be explained by the difference in expected proton consumption due to net PCr hydrolysis. However, despite buffering by PCr hydrolysis, pH ultimately decreased more in control muscle (6.1 vs. 6.3 for 5 Hz), indicating greater acid accumulation compared with beta-GPA-loaded muscles. In the superficial, predominantly fast-twitch glycolytic section of muscles clamp-frozen after 5-Hz stimulation for 150 s, lactate accumulation was twofold greater in controls. The results indicate that PCr is not essential for steady-state energy production but that the phosphate from PCr hydrolysis may be important for maximum activation of glycogenolysis and/or glycolysis.