Wilensky R L, Tranum-Jensen J, Coronel R, Wilde A A, Fiolet J W, Janse M J
Circulation. 1986 Nov;74(5):1137-46. doi: 10.1161/01.cir.74.5.1137.
Isolated preparations of rabbit interventricular septum were perfused through the coronary arteries with oxygenated Tyrode's solution and placed in a tissue bath where they were superfused as well. Transmembrane potentials were simultaneously recorded from the subendocardium with two flexibly mounted microelectrodes, one from a superficial cell, and the other from a deep cell. Ischemia was produced by stopping coronary flow while superfusion with oxygenated Tyrode's solution was maintained. After a 7 to 12 min ischemic period, the preparation was fixed by coronary perfusion with fixative while the microelectrodes remained in place. After fixation, the microelectrodes were withdrawn. Appropriate tissue blocks were cut in 4 micron serial sections and the microelectrode track was followed until the tip position was identified. Transmembrane potentials during ischemia were divided into two categories: "border zone" potentials (resting membrane potential [RMP] 73 +/- 3 mVe, action potential amplitude [APA] 81 +/- 13 mV, action potential duration [APD] 116 +/- 48 msec, n = 12) and "ischemic" potentials (RMP 53 +/- 4 mV, APA 44 +/- 11 mV, APD 102 +/- 42 msec, n = 8). Ischemic potentials were recorded from cells at depths greater than 560 micron below the endocardial surface and border zone potentials were recorded in a layer at between 130 and 650 micron below the surface. In a separate series of experiments, extracellular concentrations of K+ and pH were measured with ion-sensitive electrodes at different depths and, after a 10 min period of ischemia, part of the septum was placed in liquid nitrogen to allow determination of phosphocreatine (PC) levels in successive 50 to 100 micron layers. After 10 min of ischemia, extracellular K+ gradually increased from 4 to 9 mM in endocardium to a depth of 600 micron, pH fell from 7.4 to 6.6 over the same distance, and PC decreased to very low, stable levels at only 800 micron. It is concluded that in the first 10 min of acute ischemia, an endocardial border zone exists of 40 to 60 cell layers in which transmembrane potentials are affected relatively little by ischemia. Within this electrophysiologic border zone extracellular K+ was lower than 9 mM, pH was higher than 6.6, and tissue content of PC was not lower than 40% of normal. In layers deeper than 600 micron, with further development of a metabolic gradient, action potentials became markedly depressed. This electrophysiologic inhomogeneity within the ischemic subendocardium could be a factor in arrhythmogenesis during the first minutes of ischemia.
将兔室间隔的离体标本通过冠状动脉用氧合的台氏液灌注，并置于组织浴中，同时也对其进行表面灌注。用两个灵活安装的微电极同时记录心内膜下的跨膜电位，一个记录浅层细胞的，另一个记录深层细胞的。在维持氧合台氏液表面灌注的同时，通过停止冠状动脉血流造成缺血。在7至12分钟的缺血期后，在微电极仍在位的情况下，通过冠状动脉灌注固定液对标本进行固定。固定后，取出微电极。将适当的组织块切成4微米的连续切片，并追踪微电极轨迹直至确定尖端位置。缺血期间的跨膜电位分为两类：“边缘区”电位（静息膜电位[RMP]73±3mV，动作电位幅度[APA]81±13mV，动作电位持续时间[APD]116±48毫秒，n = 12）和“缺血”电位（RMP 53±4mV，APA 44±11mV，APD 102±42毫秒，n = 8）。从心内膜表面以下深度大于560微米的细胞记录到缺血电位，而在表面以下130至650微米的一层中记录到边缘区电位。在另一系列实验中，用离子敏感电极在不同深度测量细胞外K⁺浓度和pH，在10分钟缺血期后，将部分间隔置于液氮中，以测定连续50至100微米层中的磷酸肌酸（PC）水平。缺血10分钟后，心内膜至600微米深度范围内细胞外K⁺从4mM逐渐升至9mM，pH在相同距离内从7.4降至6.6，PC在仅800微米处降至非常低的稳定水平。结论是，在急性缺血的最初10分钟内，存在一个40至60个细胞层的心内膜边缘区，其中跨膜电位受缺血影响相对较小。在这个电生理边缘区内，细胞外K⁺低于9mM，pH高于6.6，PC的组织含量不低于正常的40%。在深度超过600微米的层中，随着代谢梯度的进一步发展，动作电位明显降低。缺血心内膜内的这种电生理不均匀性可能是缺血最初几分钟内心律失常发生的一个因素。
