Sekine Katsuhisa, Hibino Chiharu, Kimura Miyuki, Asami Koji
School of Health Sciences, Faculty of Medicine, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, Japan.
Bioelectrochemistry. 2007 May;70(2):532-41. doi: 10.1016/j.bioelechem.2007.01.001. Epub 2007 Jan 30.
In order to investigate the origin of large intensity the alpha-relaxation in skeletal muscles observed in dielectric measurements with extracellular electrode methods, effects of the interfacial polarization in the T-tubules on dielectric spectra were evaluated with the boundary-element method using two-dimensional models in which the structure of the T-tubules were represented explicitly. Each model consisted of a circular inclusion surrounded by a thin shell corresponding to the sarcolemma. The T-tubules were represented by simplified two types of invagination of the shell: straight invagination along the radial directions, and branched one. Each of the models was subjected to two kinds of calculations relevant to experiments with the extracellular and the intracellular electrode methods. Electrical interactions between the cells were omitted in the calculations. Both calculations showed that the dielectric spectra of the models contained two relaxation terms. The low-frequency relaxation term assigned to the alpha-relaxation depended on the structure of the T-tubules. Values of the relaxation frequency of the alpha-relaxation obtained from the two types of calculations agreed with each other. At the low-frequency limit, the permittivity obtained from the extracellular-electrode-type calculations varied in proportion to the capacitance obtained from the intracellular-electrode-type ones. These results were consistent with conventional lumped and distributed circuit models for the T-tubules. This confirms that the interfacial polarization in the T-tubules in a single muscle cell is not sufficient to explain the experimental results in which the intensity of the alpha-relaxation in the extracellular-electrode-type experiments exceeded the intensity expected from the results of the intracellular-electrode-type experiments. The high-frequency relaxation term that was assigned to the beta-relaxation was also affected by the T-tubule structure in the calculations relevant to the extracellular-electrode-type experiments.
为了研究用细胞外电极法进行介电测量时在骨骼肌中观察到的高强度α弛豫的起源，使用二维模型，通过边界元法评估了T小管中界面极化对介电谱的影响，其中T小管的结构被明确表示。每个模型由一个被对应于肌膜的薄壳包围的圆形内含物组成。T小管由壳的两种简化内陷表示：沿径向的直线内陷和分支内陷。每个模型都进行了与细胞外和细胞内电极法实验相关的两种计算。计算中忽略了细胞之间的电相互作用。两种计算都表明模型的介电谱包含两个弛豫项。归因于α弛豫的低频弛豫项取决于T小管的结构。从两种计算中获得的α弛豫的弛豫频率值相互一致。在低频极限下，从细胞外电极类型计算中获得的介电常数与从细胞内电极类型计算中获得的电容成比例变化。这些结果与T小管的传统集总电路和分布电路模型一致。这证实了单个肌肉细胞中T小管的界面极化不足以解释细胞外电极类型实验中α弛豫强度超过细胞内电极类型实验结果预期强度的实验结果。在与细胞外电极类型实验相关的计算中，归因于β弛豫的高频弛豫项也受到T小管结构的影响。
