Pathare Neeti, Vandenborne Krista, Liu Min, Stevens Jennifer E, Li Ye, Frimel Tiffany N, Walter Glenn A
Department of Physical Therapy, University of Florida, Gainesville, FL 32610, USA.
NMR Biomed. 2008 Feb;21(2):101-10. doi: 10.1002/nbm.1162.
Muscle disuse induces a wide array of structural, biochemical, and neural adaptations in skeletal muscle, which can affect its function. We recently demonstrated in patients with an orthopedic injury that cast immobilization alters the resting P(i) content of skeletal muscle, which may contribute to loss of specific force. The goal of this study was to determine the direct effect of disuse on the basal phosphate content in skeletal muscle in an animal model, avoiding the confounding effects of injury/surgery. (31)P and (1)H MRS data were acquired from the gastrocnemius muscle of young adult mice (C57BL6 female, n = 8), at rest and during a reversible ischemia experiment, before and after 2 weeks of cast immobilization. Cast immobilization resulted in an increase in resting P(i) content (75%; p < 0.001) and the P(i) to phosphocreatine (PCr) ratio (P(i)/PCr; 80%, p < 0.001). The resting concentrations of ATP, PCr and total creatine (PCr + creatine) and the intracellular pH were not significantly different after immobilization. During ischemia (30 min), PCr concentrations decreased to 54 +/- 2% and 52 +/- 6% of the resting values in pre-immobilized and immobilized muscles, respectively, but there were no detectable differences in the rates of P(i) increase or PCr depletion (0.55 +/- 0.01 mM min(-1) and 0.52 +/- 0.03 mM min(-1) before and after immobilization, respectively; p = 0.78). At the end of ischemia, immobilized muscles had a twofold higher phosphorylation potential ([ADP][P(i)]/[ATP]) and intracellular buffering capacity (3.38 +/- 0.54 slykes vs 6.18 +/- 0.57 slykes). However, the rate of PCr resynthesis (k(PCr)) after ischemia, a measure of in vivo mitochondrial function, was significantly lower in the immobilized muscles (0.31 +/- 0.04 min(-1)) than in pre-immobilized muscles (0.43 +/- 0.04 min(-1)). In conclusion, our findings indicate that 2 weeks of cast immobilization, independent of injury-related alterations, leads to a significant increase in the resting P(i) content of mouse skeletal muscle. The increase in P(i) with muscle disuse has a significant effect on the cytosolic phosphorylation potential during transient ischemia and increases the intracellular buffering capacity of skeletal muscle.
肌肉废用会在骨骼肌中引发一系列结构、生化和神经适应性变化，这会影响其功能。我们最近在骨科损伤患者中发现，石膏固定会改变骨骼肌的静息无机磷（P(i)）含量，这可能是导致比肌力丧失的原因之一。本研究的目的是在动物模型中确定废用对骨骼肌基础磷酸盐含量的直接影响，避免损伤/手术带来的混杂效应。在成年幼鼠（C57BL6雌性，n = 8）的腓肠肌中，于石膏固定2周前后，分别在静息状态以及可逆性缺血实验过程中采集了³¹P和¹H磁共振波谱（MRS）数据。石膏固定导致静息P(i)含量增加（75%；p < 0.001）以及P(i)与磷酸肌酸（PCr）的比率（P(i)/PCr；80%，p < 0.001）升高。固定后，ATP、PCr和总肌酸（PCr + 肌酸）的静息浓度以及细胞内pH值无显著差异。在缺血（30分钟）期间，预固定和固定后肌肉中的PCr浓度分别降至静息值的54±2%和52±6%，但P(i)增加速率或PCr消耗速率无明显差异（固定前和固定后分别为0.55±0.01 mM·min⁻¹和0.52±0.03 mM·min⁻¹；p = 0.78）。在缺血结束时，固定的肌肉具有两倍高的磷酸化电位（[ADP][P(i)]/[ATP]）和细胞内缓冲能力（3.38±0.54 slykes对6.18±0.57 slykes）。然而，缺血后PCr再合成速率（k(PCr)），即体内线粒体功能的一项指标，在固定的肌肉中（0.31±0.04 min⁻¹）显著低于预固定的肌肉（0.43±0.04 min⁻¹）。总之，我们的研究结果表明，2周的石膏固定，独立于损伤相关的改变，会导致小鼠骨骼肌静息P(i)含量显著增加。肌肉废用导致的P(i)增加对短暂缺血期间的胞质磷酸化电位有显著影响，并增加了骨骼肌的细胞内缓冲能力。
