Haws C, Krouse M E, Xia Y, Gruenert D C, Wine J J
Cystic Fibrosis Research Laboratory, Stanford University, California 94305-2130.
Am J Physiol. 1992 Dec;263(6 Pt 1):L692-707. doi: 10.1152/ajplung.1992.263.6.L692.
The cystic fibrosis (CF) gene codes for CF transmembrane regulator (CFTR), a small-conductance linear Cl- channel, but numerous studies have identified a larger conductance, rectifying Cl- channel as the adenosine 3',5'-cyclic monophosphate (cAMP)-regulated channel that is defective in airway cells. We examined Cl- conductance in a bronchial epithelial cell line that expresses CFTR, 16HBE14o-, (CFTR+) and in an airway cell line that does not, 9HTEo-/S, (CFTR-). Ionomycin or hypotonic Ringer increased iodide efflux from both cell lines; however, forskolin increased iodide efflux or whole cell Cl- currents only in CFTR+ cells. Forskolin-stimulated whole cell currents were linear, voltage independent, and blocked by iodide. Cell-attached and outside-out patches from confluent CFTR+ but not CFTR- cells revealed 6-pS channels having linear current-voltage relations, permselectivity Cl > I (partial block by external iodide), and little or no inhibition by 5-nitro-2-(3-phenylpropylamino)-benzoate. The number of active channels per patch increased from 0.6 to 3.0 after forskolin. Channels closed after excision with tau = 4 s, but activity could be prolonged with ATP or protein kinase A plus ATP. Channels were modeled with one open and four closed states and show apparent cooperativity in gating. Rectifying Cl- channels previously implicated in CF were not seen in cell-attached recordings from either cell line but were abundant in excised patches from both cell lines. Thus CFTR channels are the pathway for cAMP-mediated Cl- conductance in these human airway cells, Ca2+ and swelling-induced channels do not require CFTR, and CFTR-cells display a CF phenotype.
囊性纤维化（CF）基因编码囊性纤维化跨膜调节因子（CFTR），这是一种小电导线性氯离子通道，但大量研究已确定一种更大电导的整流氯离子通道是气道细胞中受3',5'-环磷酸腺苷（cAMP）调节的有缺陷通道。我们检测了表达CFTR的支气管上皮细胞系16HBE14o-（CFTR+）和不表达CFTR的气道细胞系9HTEo-/S（CFTR-）中的氯离子电导。离子霉素或低渗林格液增加了两个细胞系的碘外流；然而，福斯高林仅在CFTR+细胞中增加碘外流或全细胞氯离子电流。福斯高林刺激的全细胞电流呈线性、电压依赖性，并被碘阻断。汇合的CFTR+细胞而非CFTR-细胞的细胞贴附式和外翻膜片显示出6-pS通道，其具有线性电流-电压关系，通透性选择性Cl>I（被外部碘部分阻断），且几乎不受5-硝基-2-（3-苯丙基氨基）-苯甲酸抑制。福斯高林作用后，每个膜片的活性通道数量从0.6增加到3.0。通道在切除后以τ = 4 s关闭，但活性可通过ATP或蛋白激酶A加ATP延长。通道用一个开放状态和四个关闭状态进行建模，并在门控中显示出明显的协同性。先前与CF相关的整流氯离子通道在两个细胞系的细胞贴附记录中均未见到，但在两个细胞系的切除膜片中大量存在。因此，CFTR通道是这些人气道细胞中cAMP介导的氯离子电导的途径，Ca2+和肿胀诱导的通道不需要CFTR，且CFTR-细胞表现出CF表型。
