Kinsey S T, Locke B R, Penke B, Moerland T S
University of North Carolina at Wilmington, Department of Biological Sciences, NC 28403-3297, USA.
NMR Biomed. 1999 Feb;12(1):1-7. doi: 10.1002/(sici)1099-1492(199902)12:1<1::aid-nbm539>3.0.co;2-v.
The time- and orientational-dependence of phosphocreatine (PCr) diffusion was measured using pulsed-field gradient nuclear magnetic resonance (PFG-NMR) as a means of non-invasively probing the intracellular diffusive barriers of skeletal muscle. Red and white skeletal muscle from fish was used because fish muscle cells are very large, which facilitates the examination of diffusional barriers in the intracellular environment, and because they have regions of very homogeneous fiber type. Fish were cold-acclimated (5 degrees C) to amplify the contrast between red and white fibers. Apparent diffusion coefficients, D, were measured axially, D(axially) and radially, D(radially), in small muscle strips over a time course ranging from 12 to 700 ms. Radial diffusion was strongly time dependent in both fiber types, and D decreased with time until a steady-state value was reached at a diffusion time approximately 100 ms. Diffusion was also highly anisotropic, with D(axially) being higher than D(radially) for all time points. The time scale over which changes in D(radially) occurred indicated that the observed anisotropy was not a result of interactions with the thick and thin filament lattice of actin and myosin or restriction within the cylindrical sarcolemma, as has been previously suggested. Rather, the sarcoplasmic reticulum (SR) and mitochondria appear to be the principal intracellular structures that inhibit mobility in an orientation-dependent manner. This work is the first example of diffusional anisotropy induced by readily identifiable intracellular structures.
利用脉冲场梯度核磁共振（PFG-NMR）测量磷酸肌酸（PCr）扩散的时间和方向依赖性，以此作为一种非侵入性探测骨骼肌细胞内扩散屏障的方法。使用鱼类的红色和白色骨骼肌，是因为鱼类肌肉细胞非常大，这便于研究细胞内环境中的扩散屏障，还因为它们具有纤维类型非常均匀的区域。对鱼类进行冷驯化（5摄氏度）以增强红色和白色纤维之间的对比度。在12至700毫秒的时间范围内，在小肌肉条中轴向测量表观扩散系数D（轴向）和径向测量D（径向）。在两种纤维类型中，径向扩散都强烈依赖于时间，并且D随时间降低，直到在大约100毫秒的扩散时间达到稳态值。扩散也是高度各向异性的，在所有时间点D（轴向）都高于D（径向）。D（径向）发生变化的时间尺度表明，观察到的各向异性并非如先前所提出的那样是与肌动蛋白和肌球蛋白的粗细丝晶格相互作用或圆柱形肌膜内限制的结果。相反，肌浆网（SR）和线粒体似乎是以方向依赖方式抑制迁移率的主要细胞内结构。这项工作是由易于识别的细胞内结构引起的扩散各向异性的首个实例。
