Verkhratsky A, Hoppe D, Kettenmann H
Department of Neurobiology, University of Heidelberg, West Germany.
J Neurosci Res. 1991 Feb;28(2):200-9. doi: 10.1002/jnr.490280207.
Cultured Schwann cells are characterized by a strong outward rectification of the membrane; the threshold of the outward currents is close to the resting membrane potential of about -50 mV (Gray et al.: In Ritchie, Keynes (eds): Ion Channels in Neural Membranes. New York: Alan R. Liss, Inc., pp 145-157, 1986). These outward currents show up a heterogeneity among the cultured Schwann cells: some cells displayed inactivating, others non-inactivating outward currents (Hoppe et al.: Pflügers Arch 415:22-28, 1989). In this study we characterized the single channel currents using the patch-clamp technique in the intact patch recording configuration. The conductance of all recorded channels was 10-12 pS (5.6 mM [K+]o). These channels were K+ selective since changes in extracellular [K+] resulted in changes of the reversal potential as predicted for an exclusively K+ selective pore. The reversal potentials also predicted an intracellular [K+] of 60 mM indicating that the K+ equilibrium potential is slightly negative to the membrane potential. Analysis of the kinetic behavior of the channels resolved two different types of behaviour: 40% inactivated during a depolarizing voltage step, the others showing no sign of inactivation. The analysis of open probability and gating properties in the steady state showed up more differences between these two channel types: mean open probability peaked at about 10 mV for inactivating channels, while it continuously increased for non-inactivating channels. The inactivation time constants of averaged single channel and whole cell currents were similar and showed both a similar voltage dependency. We conclude that cultured Schwann cells express either two types of K+ channels with similar conductance or a channel which can acquire two functional states and that these channels can account for the different types of K+ currents observed in these cells.
培养的雪旺细胞的特征是膜具有强烈的外向整流；外向电流的阈值接近约-50 mV的静息膜电位（格雷等人：见里奇、凯恩斯（编）：《神经膜中的离子通道》。纽约：艾伦·R·利斯公司，第145 - 157页，1986年）。这些外向电流在培养的雪旺细胞中表现出异质性：一些细胞显示出失活的外向电流，另一些则显示非失活的外向电流（霍普等人：《普弗吕格尔斯 Archiv》415:22 - 28，1989年）。在本研究中，我们使用膜片钳技术在完整膜片记录配置下对单通道电流进行了表征。所有记录通道的电导为10 - 12 pS（细胞外[K⁺]o为5.6 mM）。这些通道对K⁺具有选择性，因为细胞外[K⁺]的变化导致反转电位的变化，这与仅对K⁺具有选择性的孔所预测的情况一致。反转电位还预测细胞内[K⁺]为60 mM，表明K⁺平衡电位略负于膜电位。对通道动力学行为的分析解析出两种不同类型的行为：在去极化电压阶跃期间40%失活，其他的则没有失活迹象。对稳态下开放概率和门控特性的分析显示这两种通道类型之间存在更多差异：失活通道的平均开放概率在约10 mV时达到峰值，而非失活通道则持续增加。平均单通道电流和全细胞电流的失活时间常数相似，并且都表现出相似的电压依赖性。我们得出结论，培养的雪旺细胞表达两种电导相似的K⁺通道类型，或者表达一种可以获得两种功能状态的通道，并且这些通道可以解释在这些细胞中观察到的不同类型的K⁺电流。
