Kriebel M E
J Gen Physiol. 1967 Sep;50(8):2097-107. doi: 10.1085/jgp.50.8.2097.
The tubular heart of tunicates is composed of a single layer of myoendothelial cells. The direction of contraction reverses every few minutes. The conduction times in both directions are the same. Conduction velocity was greatest in the middle of the arms of the V-shaped heart and slowest in the apex. The greater the heart length, the greater was the conduction velocity. The Q(10) of conduction velocity was 2-2.3. Removal of the raphe which attaches the heart to the pericardium and removal of a line of undifferentiated cells opposite the raphe did not change the conduction velocity or prevent the heart from reversing the direction of conduction. The median resting potential of 42 cells was -71 mv and the median action potential was 75 mv. At 20 degrees C the duration of the action potential was 1.2 sec and the maximal rate of depolarization was 3-10 v/sec. An increase in the beat frequency produced by electrically stimulating the heart decreased the resting potential, rate of rise, the duration, and the overshoot of the action potential. The shape of the action potential was sometimes different in the two directions of conduction. The electrophysiological evidence indicates only one cell type and suggests that the mode of the spread of excitation is by local current flow from cell to cell.
被囊动物的管状心脏由单层肌内皮细胞组成。收缩方向每隔几分钟就会反转一次。两个方向的传导时间相同。传导速度在V形心脏臂的中部最大，在顶端最慢。心脏长度越长，传导速度越快。传导速度的Q(10)为2 - 2.3。去除将心脏与心包相连的中缝以及去除中缝对面一排未分化细胞，并未改变传导速度，也未阻止心脏反转传导方向。42个细胞的静息电位中位数为 -71毫伏，动作电位中位数为75毫伏。在20摄氏度时，动作电位持续时间为1.2秒，最大去极化速率为3 - 10伏/秒。通过电刺激心脏产生的搏动频率增加会降低静息电位、上升速率、动作电位的持续时间和超射值。动作电位的形状在两个传导方向上有时会有所不同。电生理证据仅表明存在一种细胞类型，并表明兴奋传播方式是通过细胞间的局部电流流动。
