Rozanski G J
Masonic Medical Research Laboratory, Utica, New York 13504.
Am J Physiol. 1987 Oct;253(4 Pt 2):H720-7. doi: 10.1152/ajpheart.1987.253.4.H720.
Subsidiary atrial automaticity generated by cardiac fibers of the rabbit tricuspid valve was studied in vitro with the use of standard microelectrode techniques. The time course of diastolic depolarization of leading pacemaker fibers was characteristically biphasic over a potential range of -80 to -55 mV, with a brief primary phase of relatively steep slope and a longer secondary phase of lesser slope. The regenerative upstroke of pacemaker potentials was suppressed by cobalt ions and varied with changes in extracellular Ca2+ concentration in a manner suggesting a slow channel process. The time course of each diastolic phase, estimated by measuring slope, varied in a reproducible manner with changes in membrane potential elicited with long duration current pulses. Cesium ions reduced the slope of both diastolic phases at all potentials with greater effects on the primary diastolic phase, but spontaneous activity in the absence of current pulses was not significantly altered. Furthermore, pacemaker activity varied with changes in extracellular K+ concentration and in response to barium ions in manners suggesting the presence of a decaying K+ conductance. These experiments demonstrate the utility of valve tissue as a model of subsidiary atrial pacemaker activity and suggest the presence of current systems qualitatively similar to those observed in the sinoatrial node.
利用标准微电极技术在体外研究了兔三尖瓣心脏纤维产生的附属心房自律性。主导起搏纤维舒张期去极化的时间进程在-80至-55 mV的电位范围内具有典型的双相性，具有相对较陡斜率的短暂初级阶段和斜率较小的较长次级阶段。起搏电位的再生性上升被钴离子抑制，并随着细胞外Ca2+浓度的变化而变化，这表明存在一个缓慢通道过程。通过测量斜率估计的每个舒张期阶段的时间进程，随着长时间电流脉冲引起的膜电位变化以可重复的方式变化。铯离子在所有电位下均降低了两个舒张期阶段的斜率，对初级舒张期阶段的影响更大，但在无电流脉冲时的自发活动没有明显改变。此外，起搏活动随着细胞外K+浓度的变化以及对钡离子的反应而变化，这表明存在衰减的K+电导。这些实验证明了瓣膜组织作为附属心房起搏活动模型的实用性，并表明存在与窦房结中观察到的电流系统在性质上相似的电流系统。
