Fu Xiao Wen, Nurse Colin, Cutz Ernest
Division of Pathology, Department of Pediatric Laboratory Medicine, The Research Institute, The Hospital for Sick Children and University of Toronto, Toronto, Ontario M5G 1X8, Canada.
Am J Physiol Lung Cell Mol Physiol. 2007 Oct;293(4):L892-902. doi: 10.1152/ajplung.00098.2007. Epub 2007 Jul 20.
Pulmonary neuroepithelial bodies (NEB) form innervated cell clusters that express voltage-activated currents and function as airway O(2) sensors. We investigated A-type K(+) currents in NEB cells using neonatal rabbit lung slice preparation. The whole cell K(+) current was slowly inactivating with activation threshold of approximately -30 mV. This current was blocked approximately 27% by blood-depressing substance I (BDS-I; 3 microM), a selective blocker of Kv3.4 subunit, and reduced approximately 20% by tetraethylammonium (TEA; 100 microM). The BDS-I-sensitive component had an average peak value of 189 +/- 14 pA and showed fast inactivation kinetics that could be fitted by one-component exponential function with a time constant of (tau1) 77 +/- 10 ms. This Kv slowly inactivating current was also blocked by heteropodatoxin-2 (HpTx-2; 0.2 microM), a blocker of Kv4 subunit. The HpTx-2-sensitive current had an average peak value of 234 +/- 23 pA with a time constant (tau) 82 +/- 11 ms. Hypoxia (Po(2) = 15-20 mmHg) inhibited the slowly inactivating K(+) current by approximately 47%, during voltage steps from -30 to +30 mV, and no further inhibition occurred when TEA was combined with hypoxia. Nicotine at concentrations of 50 and 100 microM suppressed the slowly inactivating K(+) current by approximately 24 and approximately 40%, respectively. This suppression was not reversed by mecamylamine suggesting a direct effect of nicotine on these K(+) channels. In situ hybridization experiments detected expression of mRNAs for Kv3.4 and Kv4.3 subunits, while double-label immunofluorescence confirmed membrane localization of respective channel proteins in NEB cells. These studies suggest that the hypoxia-sensitive current in NEB cells is carried by slowly inactivating A-type K(+) channels, which underlie their oxygen-sensitive potassium currents, and that exposure to nicotine may directly affect their function, contributing to smoking-related lung disease.
肺神经上皮小体（NEB）形成有神经支配的细胞簇，这些细胞簇表达电压激活电流并作为气道氧气传感器发挥作用。我们使用新生兔肺切片制备物研究了NEB细胞中的A型钾电流。全细胞钾电流缓慢失活，激活阈值约为 -30 mV。该电流被血液降压物质I（BDS-I；3 microM）阻断约27%，BDS-I是Kv3.4亚基的选择性阻断剂，被四乙铵（TEA；100 microM）降低约20%。BDS-I敏感成分的平均峰值为189±14 pA，表现出快速失活动力学，可用单成分指数函数拟合，时间常数（tau1）为77±10 ms。这种Kv缓慢失活电流也被异足毒素-2（HpTx-2；0.2 microM）阻断，HpTx-2是Kv4亚基的阻断剂。HpTx-2敏感电流的平均峰值为234±23 pA，时间常数（tau）为82±11 ms。低氧（Po(2)=15 - 20 mmHg）在电压从 -30 mV 步进到 +30 mV 期间，抑制缓慢失活的钾电流约47%，当TEA与低氧联合时未发生进一步抑制。浓度为50和100 microM的尼古丁分别抑制缓慢失活的钾电流约24%和约40%。这种抑制作用不能被美加明逆转，表明尼古丁对这些钾通道有直接作用。原位杂交实验检测到Kv3.4和Kv4.3亚基的mRNA表达，而双标免疫荧光证实了相应通道蛋白在NEB细胞中的膜定位。这些研究表明，NEB细胞中对低氧敏感的电流由缓慢失活的A型钾通道携带，这些通道是其氧敏感钾电流的基础，并且接触尼古丁可能直接影响其功能，导致与吸烟相关的肺部疾病。
