Wang K W, Hladky S B
Department of Pharmacology, University of Cambridge, United Kingdom.
Biophys J. 1994 Oct;67(4):1473-83. doi: 10.1016/S0006-3495(94)80621-6.
The effects of static and low-frequency magnetic fields on gramicidin A channels have been investigated using bilayer patch clamp recording and a bridge technique capable of detecting 0.3% changes in the conductance of glyceryl monooleate membranes containing many channels. In the bridge technique the conductance was assessed using 10-ms voltage pulses applied at 10 Hz. Measurements were made for LiCl, KCl, and CsCl using magnetic fields of 50, 100, 500, and 5000 microT with the frequency scanned from 10-200 Hz. The combinations of static and low-frequency fields employed include the "cyclotron resonance" conditions at which effects had been predicted to occur. In no case was there any detectable change in conductance when the magnetic fields were applied or changed. Potassium currents through single gramicidin channels have been recorded for patches in which several channels may be open at once. Fields were applied for 2 min periods interleaved with 2 min controls. Methods have been developed to analyze the multichannel records to reveal the amplitude and duration of the channels together with the frequency, depth, and apparent period of flickers. No significant differences were observed between the control and field-exposed recording periods. The peak of the distribution of opening and closing transitions always coincided for fields on and off within the resolution, 0.4%, of the recordings. There are at least two types of flicker, one with typical period less than 0.1 ms, the other with typical period from 0.3-0.8 ms. Most of the latter were not complete closures with the conductance during a flicker 15-20% above the level for a full closure.
利用双层膜片钳记录技术和一种能够检测含有多个通道的单油酸甘油酯膜电导0.3%变化的桥式技术，研究了静态和低频磁场对短杆菌肽A通道的影响。在桥式技术中，使用以10 Hz施加的10 ms电压脉冲来评估电导。使用50、100、500和5000 μT的磁场对LiCl、KCl和CsCl进行测量，频率范围从10 - 200 Hz扫描。所采用的静态和低频场的组合包括预测会产生效应的“回旋共振”条件。在施加或改变磁场时，在任何情况下都没有检测到电导的变化。对于可能同时有多个通道开放的膜片，记录了通过单个短杆菌肽通道的钾电流。磁场施加2分钟，期间穿插2分钟的对照。已经开发出分析多通道记录的方法，以揭示通道的幅度和持续时间以及闪烁的频率、深度和表观周期。在对照和暴露于磁场的记录期间未观察到显著差异。在记录分辨率0.4%范围内，磁场开启和关闭时，开放和关闭转变分布的峰值始终一致。至少有两种类型的闪烁，一种典型周期小于0.1 ms，另一种典型周期为0.3 - 0.8 ms。大多数后者不是完全关闭，闪烁期间的电导比完全关闭时的水平高15 - 20%。
