Overholt J L, Ficker E, Yang T, Shams H, Bright G R, Prabhakar N R
Departments of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA.
J Neurophysiol. 2000 Mar;83(3):1150-7. doi: 10.1152/jn.2000.83.3.1150.
Direct evidence for a specific K(+) channel underlying the resting membrane potential in glomus cells of the carotid body has been absent. The product of the human ether-a-go-go-related gene (HERG) produces inward rectifier currents that are known to contribute to the resting membrane potential in other neuronal cells. The goal of the present study was to determine whether carotid body glomus cells express HERG-like K(+) current, and if so, to determine whether a HERG-like current regulates the resting membrane potential. Freshly dissociated rabbit glomus cells under whole cell voltage clamp exhibited slowly decaying outward currents that activated 20-30 mV positive to the resting membrane potential. Raising extracellular K(+) revealed a slowly deactivating inward tail current indicative of HERG-like K(+) current. HERG-like currents were not found in cells resembling type II cells. The HERG-like current was blocked by dofetilide (DOF) in a concentration-dependent manner (IC(50) = 13 +/- 4 nM, mean +/- SE) and high concentrations of Ba(2+) (1 and 10 mM). The biophysical and pharmacological characteristics of this inward tail current suggest that it is conducted by a HERG-like channel. The steady-state activation properties of the HERG-like current (V(h) = -44 +/- 2 mV) suggest that it is active at the resting membrane potential in glomus cells. In whole cell, current-clamped glomus cells (average resting membrane potential, - 48 +/- 4 mV), DOF, but not tetraethylammonium, caused a significant (13 mV) depolarizing shift in the resting membrane potential. Using fluorescence imaging, DOF increased Ca(2+) in isolated glomus cells. In an in-vitro carotid body preparation, DOF increased basal sensory discharge in the carotid sinus nerve in a concentration-dependent manner. These results demonstrate that glomus cells express a HERG-like current that is active at, and responsible for controlling the resting membrane potential.
目前尚无直接证据表明颈动脉体球细胞静息膜电位背后存在特定的钾离子通道。人类醚 - 去极化相关基因（HERG）的产物可产生内向整流电流，已知该电流对其他神经元细胞的静息膜电位有影响。本研究的目的是确定颈动脉体球细胞是否表达类HERG钾离子电流，如果是，则确定类HERG电流是否调节静息膜电位。在全细胞电压钳制下，新鲜分离的兔球细胞表现出缓慢衰减的外向电流，该电流在比静息膜电位正20 - 30 mV时激活。提高细胞外钾离子浓度可显示出缓慢失活的内向尾电流，表明存在类HERG钾离子电流。在类似II型细胞的细胞中未发现类HERG电流。类HERG电流被多非利特（DOF）以浓度依赖的方式阻断（IC50 = 13 ± 4 nM，平均值 ± 标准误），以及高浓度的钡离子（1和10 mM）。这种内向尾电流的生物物理和药理学特性表明它是由类HERG通道传导的。类HERG电流的稳态激活特性（Vh = -44 ± 2 mV）表明它在球细胞的静息膜电位时处于激活状态。在全细胞电流钳制的球细胞中（平均静息膜电位，-48 ± 4 mV），DOF而非四乙铵导致静息膜电位发生显著的（13 mV）去极化偏移。使用荧光成像技术，DOF可增加分离球细胞内的钙离子浓度。在体外颈动脉体标本中，DOF以浓度依赖的方式增加颈动脉窦神经的基础感觉放电。这些结果表明，球细胞表达一种类HERG电流，该电流在静息膜电位时处于激活状态，并负责控制静息膜电位。
