PH REGULATION IN SKELETAL MUSCLE--DESIGN & PLASTICITY

脊椎动物骨骼肌调节细胞内 pH（pHi）很少受到关注，尽管事实上， pHi的变化可以对肌肉收缩产生显著影响， 和新陈代谢。 只有两块肌肉，青蛙的半腱肌 和老鼠的比目鱼肌，都有膜运输系统 负责调节pH值。 拟议 研究，三个问题将得到解决，目的是 更全面地定义肌肉细胞功能 pHi调节。 i）青蛙的pH调节系统 肌肉（Na/H和（Na + HCO3）/C1交换器）定位于 表面膜，T管膜或两者？ 将通过研究实现转运蛋白的定位：pH 恢复（用玻璃电极）在甘油休克纤维（其T 小管囊状化，不再与外界接触 培养基）;由表面制备的大囊泡中的pH恢复 膜; Na摄取到由以下任一种物质制成的小泡中 表面或T管状膜;和酸挤压到T 管状管腔，使用不可渗透的pH敏感性荧光染料。 ii）未搅拌层的酸化，特别是T形管 流明，限制的速度和程度的pHi恢复？ 的影响 将通过测量单个样品中的回收率来评估未搅拌层 vs.多细胞制剂和暴露于不同环境中的纤维 外部缓冲液浓度。 酸挤压对 未搅拌层中的pH将使用pH直接测定。 敏感电极靠近纤维表面，并使用pH- 敏感的荧光染料。 （三）如何 红肌纤维和白色肌纤维调节pH能力不同？ 缓冲能力、pHi恢复的速率和程度，以及 负责恢复的运输系统的特性将 在小鼠比目鱼肌（红色）和EDL（白色）肌肉中进行比较。 这些研究将代表第一次本地化的载体 系统在肌肉膜，第一次直接测量pH值 与pH调节的第一个相关性 具有细胞代谢和收缩特性的能力。 除了在这些研究中获得的对pH调节的基本理解之外， 研究，pH调节的详细知识可能会揭示 肌营养不良症的病因和/或症状， 肌强直 这些疾病的主要病变之一是 改变膜的性质，导致改变 收缩和代谢过程。 在pHi中变化的作用 调节能力可能在这种病理学中起作用， 研究了

The ability of vertebrate skeletal muscle to regulate intracellular pH (pHi) has received very little attention, despite the fact that changes in pHi can have a marked effect on muscle contraction and metabolism. Only in two muscles, the frog semitendinosus and the mouse soleus, have the membrane transport systems responsible for pH regulation been described. In the proposed research, three questions will be addressed with the aim of defining more fully the relationship between muscle cell function and pHi regulation. i) Are the pH-regulating systems in frog muscle (Na/H and (Na+HCO3)/C1 exchangers) localized to the surface membrane, the T tubular membrane or both? Localization of the transporters will be achieved by studying: pH recover (with glass electrodes) in glycerol-shocked fibers (whose T tubules vesiculate and are no longer in contact with the external medium); pH recovery in large vesicles made from surface membrane; Na uptake into small vesicles made from either surface or T tubular membrane; and acid extrusion into the T tubular lumen, using impermeable pH-sensitive fluorescent dyes. ii) Does acidification of unstirred layers, especially the T tubular lumen, limit the rate and extent of pHi recovery? The effect of unstirred layers will be assessed by measuring recovery in single vs. multicellular preparations and in fibers exposed to varying external buffer concentrations. The effect of acid extrusion on the pH in unstirred layers will be directly determined using pH- sensitive electrodes close to the fiber surface and using pH- sensitive fluorescent dyes in the T tubular lumen. iii) How does the ability to regulate pH differ in red vs. white muscle fibers? The buffering power, the rate and extent of pHi recovery, and the properties of the transport systems responsible for recovery will be compared in mouse soleus (red) and EDL (white) muscles. These studies will represent the first localization of a carrier system in muscle membrane, the first direct measurements of pH in the T tubular lumen and the first correlation of pH-regulating capabilities with cellular metabolic and contractile properties. Beyond the basic understanding of pH regulation gained in these studies, detailed knowledge of pH regulation may shed light on the etiology and/or symptoms of the muscular dystrophies and myotonias. One of the primary lesions of these diseases is an alteration of membrane properties which results in altered contractile and metabolic processes. The role that changes in pHi regulating ability may play in such pathology remains to be studied.