Blandino J K, Viglione M P, Bradley W A, Oie H K, Kim Y I
Department of Biomedical Engineering, University of Virginia School of Medicine, Charlottesville 22908, USA.
J Membr Biol. 1995 Jan;143(2):153-63. doi: 10.1007/BF00234661.
Sodium channels of human small-cell lung cancer (SCLC) cells were examined with whole-cell and single-channel patch clamp methods. In the tumor cells from SCLC cell line NCI-H146, the majority of the voltage-gated Na+ channels are only weakly tetrodotoxin (TTX)-sensitive (Kd = 215 nM). With the membrane potential maintained at -60 to -80 mV, these cells produced all-or-nothing action potentials in response to depolarizing current injection (> 20 pA). Similar all-or-nothing spikes were also observed with anodal break excitation. Removal of external Ca2+ did not affect the action potential production, whereas 5 microM TTX or substitution of Na+ with choline abolished it. Action potentials elicited in the Ca(2+)-free condition were reversibly blocked by 4 mM MnCl2 due to the Mn(2+)-induced inhibition of voltage-dependent sodium currents (INa). Therefore, Na+ channels, not Ca2+ channels, underlie the excitability of SCLC cells. Whole-cell INa was maximal with step-depolarizing stimulations to 0 mV, and reversed at +45.2 mV, in accord with the predicted Nernst equilibrium potential for a Na(+)-selective channel. INa evoked by depolarizing test potentials (-60 to +40 mV) exhibited a transient time course and activation/inactivation kinetics typical of neuronal excitable membranes; the plot of the Hodgkin-Huxley parameters, m infinity and h infinity, also revealed biophysical similarity between SCLC and neuronal Na+ channels. The single channel current amplitude, as measured with the inside-out patch configuration, was 1.0 pA at -20 mV with a slope conductance of 12.1 pS. The autoantibodies implicated in the Lambert-Eaton myasthenic syndrome (LES), which are known to inhibit ICa and INa in bovine adrenal chromaffin cells, also significantly inhibited INa in SCLC cells. These results indicate that (i) action potentials in human SCLC cells result from the regenerative increase in voltage-gated Na+ channel conductance; (ii) fundamental characteristics of SCLC Na+ channels are the same as the classical sodium channels found in a variety of excitable cells; and (iii) in some LES patients, SCLC Na+ channels are an additional target of the pathological IgG present in the patients' sera.
采用全细胞和单通道膜片钳方法对人小细胞肺癌（SCLC）细胞的钠通道进行了检测。在SCLC细胞系NCI-H146的肿瘤细胞中，大多数电压门控Na⁺通道仅对河豚毒素（TTX）轻度敏感（解离常数Kd = 215 nM）。当膜电位维持在-60至-80 mV时，这些细胞在去极化电流注入（> 20 pA）时产生全或无动作电位。在阳极断电刺激时也观察到类似的全或无尖峰。去除细胞外Ca²⁺不影响动作电位的产生，而5 μM TTX或用胆碱替代Na⁺则使其消失。在无Ca²⁺条件下诱发的动作电位被4 mM MnCl₂可逆性阻断，这是由于Mn²⁺对电压依赖性钠电流（INa）的抑制作用。因此，SCLC细胞的兴奋性是由Na⁺通道而非Ca²⁺通道介导的。全细胞INa在阶跃去极化刺激至0 mV时最大，并在+45.2 mV时反转，这与Na⁺选择性通道的预测能斯特平衡电位一致。去极化测试电位（-60至+40 mV）诱发的INa呈现出典型的神经元可兴奋膜的瞬态时间过程和激活/失活动力学；Hodgkin-Huxley参数m∞和h∞的曲线也揭示了SCLC和神经元Na⁺通道之间的生物物理相似性。采用内面向外膜片钳配置测量的单通道电流幅度在-20 mV时为1.0 pA，斜率电导为12.1 pS。已知与兰伯特-伊顿肌无力综合征（LES）相关的自身抗体可抑制牛肾上腺嗜铬细胞中的ICa和INa，在SCLC细胞中也显著抑制INa。这些结果表明：（i）人SCLC细胞中的动作电位是由电压门控Na⁺通道电导的再生性增加引起的；（ii）SCLC Na⁺通道的基本特征与在各种可兴奋细胞中发现的经典钠通道相同；（iii）在一些LES患者中，SCLC Na⁺通道是患者血清中病理性IgG的另一个作用靶点。
