Leroy Claudie, Dagenais André, Berthiaume Yves, Brochiero Emmanuelle
Centre de recherche, CHUM-Hôtel-Dieu, 3850 St-Urbain, Montréal, Québec H2W 1T7, Canada.
Am J Physiol Lung Cell Mol Physiol. 2004 May;286(5):L1027-37. doi: 10.1152/ajplung.00249.2003. Epub 2004 Jan 16.
K(+) channels play a crucial role in epithelia by repolarizing cells and maintaining electrochemical gradient for Na(+) absorption and Cl(-) secretion. In the airway epithelium, the most frequently studied K(+) channels are KvLQT1 and K(Ca). A functional role for K(ATP) channels has been also suggested in the lung, where K(ATP) channel openers activate alveolar clearance and attenuate ischemia-reperfusion injury. However, the molecular identity of this channel is unknown in airway and alveolar epithelial cells (AEC). We adopted an RT-PCR strategy to identify, in AEC, cDNA transcripts for Kir channels (Kir6.1 or 6.2) and sulfonylurea receptors (SUR1, 2A, or 2B) forming K(ATP) channels. Only Kir6.1 and SUR2B were detected in freshly isolated and cultured alveolar cells. To determine the physiological role of K(+) channels in the transepithelial transport of alveolar monolayers, we studied the effect, on total short-circuit currents (I(sc)), of basolateral application of glibenclamide, an inhibitor of K(ATP) channels, as well as clofilium, charybdotoxin, clotrimazole, and iberiotoxin, inhibitors of KvLQT1 and K(Ca) channels, respectively. Interestingly, activity of the three types of K(+) channels was detected, since all tested inhibitors decreased I(sc). Furthermore, these K(+) channel inhibitors reduced amiloride-sensitive Na(+) currents (mediated by ENaC) and completely abolished stimulation of Cl(-) currents by forskolin. Conversely, pinacidil, an activator of K(ATP) channels, increased Na(+) and Cl(-) transepithelial transport by 33-35%. These results suggest the presence, in AEC, of a K(ATP) channel, formed from Kir6.1 and SUR2B subunits, which plays a physiological role, with KvLQT1 and K(Ca) channels, in Na(+) and Cl(-) transepithelial transport.
钾离子通道通过使细胞复极化并维持钠离子吸收和氯离子分泌的电化学梯度，在上皮组织中发挥关键作用。在气道上皮中，研究最频繁的钾离子通道是KvLQT1和钾钙通道。在肺中也有人提出ATP敏感性钾通道具有功能作用，其中ATP敏感性钾通道开放剂可激活肺泡清除并减轻缺血再灌注损伤。然而，在气道和肺泡上皮细胞（AEC）中，该通道的分子身份尚不清楚。我们采用逆转录聚合酶链反应（RT-PCR）策略，在AEC中鉴定形成ATP敏感性钾通道的内向整流钾通道（Kir6.1或6.2）和磺脲类受体（SUR1、2A或2B）的cDNA转录本。在新鲜分离和培养的肺泡细胞中仅检测到Kir6.1和SUR2B。为了确定钾离子通道在肺泡单层跨上皮转运中的生理作用，我们研究了ATP敏感性钾通道抑制剂格列本脲以及分别为KvLQT1和钾钙通道抑制剂的氯非铵、蝎毒素、克霉唑和iberiotoxin经基底外侧应用对总短路电流（I(sc)）的影响。有趣的是，检测到了三种类型钾离子通道的活性，因为所有测试抑制剂均降低了I(sc)。此外，这些钾离子通道抑制剂降低了氨氯地平敏感的钠离子电流（由上皮钠通道介导），并完全消除了福斯可林对氯离子电流的刺激。相反，ATP敏感性钾通道激活剂匹那地尔使钠离子和氯离子跨上皮转运增加了33% - 35%。这些结果表明，在AEC中存在由Kir6.1和SUR2B亚基形成的ATP敏感性钾通道，其与KvLQT1和钾钙通道一起在钠离子和氯离子跨上皮转运中发挥生理作用。
