Rubenstein D S, Fox L M, McNulty J A, Lipsius S L
Loyola University of Chicago, Stritch School of Medicine, Departments of Physiology and Anatomy, Maywood, IL 60153.
J Mol Cell Cardiol. 1987 Oct;19(10):965-76. doi: 10.1016/s0022-2828(87)80569-2.
Intracellular microelectrode and electron microscopic techniques were used to investigate and correlate the electrophysiology of subsidiary pacemaker activity with the presence of cells having ultrastructural characteristics of pacemaker cells i.e. P cells, in Eustachian ridge tissue isolated from cat right atrium. In addition, the electrophysiological characteristics of subsidiary pacemaker activity and the ultrastructural characteristics of P cells in Eustachian ridge were compared to those of SA node obtained from the same hearts. Action potential recordings and morphological analysis were restricted to the endocardial site of earliest activation. Electrophysiological recordings revealed that spontaneously active Eustachian ridge tissues generate slow response action potentials with pacemaker characteristics similar, although not identical, to those of SA node. These included a relatively steep diastolic slope, low maximum diastolic potential (-70 mV), rate of rise (5.5 V/s), take-off potential (-52.5 mV), a relatively large overshoot potential (+7.7 mV) and a spontaneous cycle length (948 ms) about twice as long as SA node (434 ms). Morphological analysis revealed cells with ultrastructural characteristics of P cells, that were restricted to the endocardial site of earliest pacemaker activation. Morphological measurements indicate that Eustachian ridge P cells are not significantly different from P cells in SA node of the same hearts. However, Eustachian ridge P cells exhibit a unique apposition of subsarcolemmal cisternae between cells not seen in SA node. We conclude that pacemaker cells within the Eustachian ridge generate stable, spontaneous activity via slow response pacemaker action potentials. Cells responsible for this subsidiary pacemaker activity are most likely P cell types that are similar, although not identical, to P cells in SA node.
采用细胞内微电极和电子显微镜技术，对从猫右心房分离的咽鼓管嵴组织中辅助起搏点活动的电生理学与具有起搏细胞超微结构特征（即P细胞）的细胞的存在情况进行研究并建立关联。此外，还将咽鼓管嵴中辅助起搏点活动的电生理特征和P细胞的超微结构特征与取自同一心脏的窦房结的特征进行了比较。动作电位记录和形态学分析仅限于最早激活的内膜部位。电生理记录显示，自发活动的咽鼓管嵴组织产生缓慢反应动作电位，其起搏特征与窦房结相似但不完全相同。这些特征包括相对较陡的舒张期斜率、较低的最大舒张电位（-70 mV）、上升速率（5.5 V/s）、起始电位（-52.5 mV）、相对较大的超射电位（+7.7 mV）以及自发周期长度（948 ms），约为窦房结（434 ms）的两倍。形态学分析显示，具有P细胞超微结构特征的细胞仅限于最早起搏激活的内膜部位。形态学测量表明，咽鼓管嵴P细胞与同一心脏窦房结中的P细胞无显著差异。然而，咽鼓管嵴P细胞在细胞间表现出一种窦房结中未见的肌膜下池的独特并列。我们得出结论，咽鼓管嵴内的起搏细胞通过缓慢反应起搏动作电位产生稳定的自发活动。负责这种辅助起搏活动的细胞很可能是P细胞类型，它们与窦房结中的P细胞相似但不完全相同。
