Tucker D C, Snider C, Woods W T
Department of Psychology, University of Alabama, Birmingham 35294.
Pediatr Res. 1988 Jun;23(6):637-42. doi: 10.1203/00006450-198806000-00022.
Conditions that cause pacemaker formation in the developing heart are poorly understood. Embryonic rat myocardium grafted into the anterior eye chamber of an adult rat provides a promising model system in which to study pacemaker development. Electrophysiologic mapping with two microelectrodes showed that each embryonic heart graft developed a primary pacemaker within the region of contact with the host iris. These single, primary pacemakers were found in the centers of graft-iris junctions both in grafts that originally contained the natural pacemaker (e.g. right atria and whole hearts) and in grafts that excluded the sinoatrial pacemaker region (i.e. ventricles and left atrial appendages). Pacemaker action potentials were recorded in the region identified by mapping as the origin of the impulse in 11 of 11 grafts. Action potentials recorded from surrounding working cells were similar to adult rat heart cells in maximum diastolic potential, overshoot, amplitude, and duration. In contrast, maximum upstroke velocity was consistently slower in grafts than in adult hearts. Beating of grafts slowed or stopped within 3 days after transplantation but resumed by 10-14 days at rates similar to those observed before dissection (265 +/- 12), a pattern consistent with development of a new pacemaker in oculo. The graft-iris junction is the site of blood vessel and nerve ingrowth into the graft and it is a region of contact between differentiated embryonic myocardial cells and nonmyocardial (iris epithelial) cells. The roles of these three factors (vascularization, innervation, and surface contact) in establishing the pacemaker were examined using embryonic heart cultured both in the anterior eye chamber and in vitro.
导致发育中心脏起搏器形成的条件目前尚不清楚。移植到成年大鼠前房的胚胎大鼠心肌提供了一个很有前景的模型系统，可用于研究起搏器的发育。用两个微电极进行的电生理标测显示，每个胚胎心脏移植物在与宿主虹膜接触的区域内形成了一个初级起搏器。这些单一的初级起搏器在最初包含天然起搏器的移植物（如右心房和全心）以及排除窦房结起搏器区域的移植物（即心室和左心耳）的移植物-虹膜连接处的中心被发现。在11个移植物中，有11个在标测确定为冲动起源的区域记录到了起搏器动作电位。从周围工作细胞记录的动作电位在最大舒张电位、超射、幅度和持续时间方面与成年大鼠心脏细胞相似。相比之下，移植物中的最大上升速度始终比成年心脏慢。移植物的跳动在移植后3天内减慢或停止，但在10 - 14天恢复，恢复后的速率与解剖前观察到的速率相似（265±12），这一模式与眼内新起搏器的发育一致。移植物-虹膜连接处是血管和神经长入移植物的部位，也是分化的胚胎心肌细胞与非心肌（虹膜上皮）细胞接触的区域。使用在前房和体外培养的胚胎心脏，研究了这三个因素（血管化、神经支配和表面接触）在建立起搏器中的作用。
