Acta Scientiarum Naturalium Universitatis Pekinensis

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Two Membrane Levels of Early Afterdepolarization in Sheep Purkinje Fibers and Their Possible Ionic Mechanisms

XU Jian, WANG Zhiqing, WANG Zhongmin, LIU Taifeng   

  1. State Key Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing, 100871
  • Received:1999-07-08 Online:2000-07-20 Published:2000-07-20

羊心蒲氏纤维两个水平的早后去极化及其离子机制

徐坚, 王知青, 王忠民, 刘泰逢   

  1. 北京大学生命科学学院,生物膜与膜生物工程国家重点实验室,北京,100871

Abstract: Sheep Purkinje fibers were used to investigate early afterdepolarization (EAD) generation and its possible ionic mechanisms with bielectrode voltage clamp technique. Under low K+ (2.5mmol/LK+) superfusion, two levels (-25 and -55mV) of EAD could be induced on the background of automaticity. The bursts in low membrane level EAD were abolished by nifedipine (2.0μmol/L) whereas those in high membrane level were abolished by lidocaine (10μmol/L) and low temperature (30℃). The quasi-steady-state - relationship of the background currents obtained with step and ramp voltage clamp showed a negative phase in outward part of the rectification under 5.0mmol/LK+ superfusion, while an inward current phase appeared between -55 and -25mV level in the curve under 2.5 K+ treatment. Under the condition of EAD generation, the low and high membrane level (-25 and -55mV) of voltage were clamped during the repolarization phase of action potential. On low membrane level of -25mV, a slow inward current similar to Si occurred followed by a slight outward current like Ik, whereas on high level of -55mV, a continued inward current looked like If occurred. It was suggested that the two levels of plateau were based on the two zero current point in - curve under 2.5mmol/LK+ superfusion, whereas bursts were based on the Si, mainly ICa, for the low membrane level and If (and slow inactivated INa) for the high one.

Key words: purkinje fibers, action potential, early afterdepolarization, low K+, nifedipine, lidocaine, ICa, If

摘要: 用双电极电压箝制技术研究了羊心蒲氏纤维早后去极化(Early afterdepolarization, EAD)的发生及其离子机制。在低钾生理溶液(2.5mmol/LK+)灌流下,于自发活动基础上可诱发出2个膜电位水平(-25与-55mV)的EAD。低电位水平的发放可被硝苯吡啶(2.0μmol/L)消除,而高电位的发放可由利多卡因(10μmol/L)或低温(30℃)所抑制。在正常钾浓度(5.0mmol/L)灌流下,无论用阶梯法或斜坡法进行电压钳制,羊心蒲氏纤维的背景电流I-V曲线,均呈外向整流特性。而在低钾灌流条件下,该曲线在-55及-25mV处分别形成跨越(cross over),即出现一个内向电流区。在低钾灌流并伴有EAD的情况下,于动作电位复极相的低及高电位处(-25与-55mV)分别进行电压钳制。研究发现:当电压钳制在-25mV时出现一个与ICa相似的慢内向偏转,随之为一缓慢的IK样电流。当电压钳制在-55mV时,出现的内向电流与If类似。由以上结果可以推测,产生羊心蒲氏纤维EAD的2个膜电位平台是基于背景电流I-V曲线上跨越区(即-25mV及-55mV)的两个零电流点。低电位水平的触发发放基于ICa,而高电位水平的发放基于If及慢失活INa

关键词: 羊心蒲氏纤维, 动作电位, 早后去极化, 低钾, 硝苯吡啶, 利多卡因, ICa, If

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