Kriebel M E
J Gen Physiol. 1968 Jul;52(1):46-59. doi: 10.1085/jgp.52.1.46.
The tubular ascidian heart is composed of a single layer of cells joined together by apical (zonulae occludentes) and spot (maculae occludentes) nexuses. Intercalated discs or desmosomes were not observed in this tissue. Rectangular pulses of current were applied across the opened and flattened myocardium. Assuming that all the transepithelial current flowed through a uniform gap between cells, the resistivity in the gap must be very high compared to that in bulk solution. It is likely, therefore, that the gap width is of the order of an ionic radius or smaller. Assuming that all the transepithelial current flowed through the cells and that the inner and outer membranes had the same resistivity, the membrane resistivity was about 210 ohms cm(2) and the membrane capacitance was about 1.6 microF per cm(2). The myocardial cells were found to be in electrical continuity with each other through the nexuses since current could be passed through a strip of myocardium in a sucrose gap. Assuming that the longitudinal resistance of the cytoplasm was negligible, the cell-to-cell resistivity of the nexuses was 0.2 ohm cm(2). It is concluded that the nexuses provide a low resistance pathway between cells and a transepithelial barrier.
管状海鞘心脏由单层细胞组成，这些细胞通过顶端（紧密连接）和点状（闭锁斑）连接相连。在该组织中未观察到闰盘或桥粒。将矩形电流脉冲施加到打开并展平的心肌上。假设所有跨上皮电流都流经细胞间均匀的间隙，那么该间隙的电阻率必定比本体溶液中的电阻率高得多。因此，间隙宽度可能在离子半径量级或更小。假设所有跨上皮电流都流经细胞，且内膜和外膜具有相同的电阻率，那么膜电阻率约为210欧姆·平方厘米，膜电容约为每平方厘米1.6微法。由于电流可以在蔗糖间隙中的一条心肌条上通过，发现心肌细胞通过连接彼此电连续。假设细胞质的纵向电阻可忽略不计，连接的细胞间电阻率为0.2欧姆·平方厘米。得出的结论是，连接在细胞间提供了低电阻通路和跨上皮屏障。
