Spach M S, Miller W T, Miller-Jones E, Warren R B, Barr R C
Circ Res. 1979 Aug;45(2):188-204. doi: 10.1161/01.res.45.2.188.
This paper considers a quantitative description of intracellular and transmembrane currents in anisotropic muscle, with emphasis on the factors that determine the extracellular potentials. Although Vmax of the intracellular action potential had no relation to changes in conduction velocity in anisotropic tissue with constant membrane properties, the extracellular waveforms were quite sensitive to velocity changes. Large amplitude biphasic deflection occurred in the fast areas, and in the slow areas the waveforms were of lower amplitude and triphasic in shape; i.e., negative potentials preceded the biphasic positive-negative deflection. The extracellular potentials were simulated on the bases of a model of intracellular currents, and the theoretical and measured results showed good agreement. In tissue with anisotropic conductivity, the relationship between the spatial intracellualr potential gradient and the magnitude of the extracellular potential of the excitation wave was opposite to the classical relationship in isotropic tissue. Due to the influence of the effective intracellular conductivity on the spread of intracellular currents and on conduction velocity, in anisotropic tissue the extracellular potential decreased as the intracellular potential gradient increased. The peak values of the positive and negative potentials and the spatial distribution of the potential gradients varied considerably along the activation front. These findings were accounted for by differences in the distribution and spatial extent of the transmembrane currents, which were determined by the intracellular currents. The theoretical analysis showed that intracellular and transmembrane currents were proportional to the local conduction velocities of the wavefront. Thereby, it was not possible to have a "uniform layer" of current when there were differences in conduction velocity along the length of the excitation wave. The implications of the analysis are considerable, since the gratifying agreement between the theoretical and measured results indicates that the details of the extracellular waveforms can be explained on the basis of the distribution of intracellular currents; i.e., extracellular potentials provide a sensitive index of intracellular current flow.
本文考虑对各向异性肌肉中的细胞内电流和跨膜电流进行定量描述，重点关注决定细胞外电位的因素。尽管在具有恒定膜特性的各向异性组织中，细胞内动作电位的最大速率（Vmax）与传导速度的变化无关，但细胞外波形对速度变化相当敏感。在快速区域出现大幅度双相偏转，而在慢速区域，波形幅度较小且呈三相；即负电位先于双相正负偏转出现。基于细胞内电流模型对细胞外电位进行了模拟，理论结果与测量结果吻合良好。在具有各向异性电导率的组织中，细胞内空间电位梯度与兴奋波细胞外电位大小之间的关系与各向同性组织中的经典关系相反。由于有效细胞内电导率对细胞内电流传播和传导速度的影响，在各向异性组织中，细胞外电位随着细胞内电位梯度的增加而降低。正负电位的峰值以及电位梯度的空间分布沿激活前沿变化很大。这些发现可以通过跨膜电流的分布和空间范围的差异来解释，而跨膜电流由细胞内电流决定。理论分析表明，细胞内电流和跨膜电流与波前的局部传导速度成正比。因此，当沿兴奋波长度的传导速度存在差异时，不可能有“均匀电流层”。该分析的意义重大，因为理论结果与测量结果之间令人满意的一致性表明，细胞外波形的细节可以基于细胞内电流的分布来解释；即细胞外电位提供了细胞内电流流动的敏感指标。
