Institut de Recherches Cliniques de Montréal (IRCM), Montreal, Quebec, Canada ; Département de Médecine, Université de Montréal, Montreal, Quebec, Canada.
PLoS One. 2013 Sep 3;8(9):e74565. doi: 10.1371/journal.pone.0074565. eCollection 2013.
Alveolar epithelial cells are involved in Na(+) absorption via the epithelial Na(+) channel (ENaC), an important process for maintaining an appropriate volume of liquid lining the respiratory epithelium and for lung oedema clearance. Here, we investigated how a 20% hypotonic shock modulates the ionic current in these cells. Polarized alveolar epithelial cells isolated from rat lungs were cultured on permeant filters and their electrophysiological properties recorded. A 20% bilateral hypotonic shock induced an immediate, but transient 52% rise in total transepithelial current and a 67% increase in the amiloride-sensitive current mediated by ENaC. Amiloride pre-treatment decreased the current rise after hypotonic shock, showing that ENaC current is involved in this response. Since Cl(-) transport is modulated by hypotonic shock, its contribution to the basal and hypotonic-induced transepithelial current was also assessed. Apical NPPB, a broad Cl(-) channel inhibitor and basolateral DIOA a potassium chloride co-transporter (KCC) inhibitor reduced the total and ENaC currents, showing that transcellular Cl(-) transport plays a major role in that process. During hypotonic shock, a basolateral Cl(-) influx, partly inhibited by NPPB is essential for the hypotonic-induced current rise. Hypotonic shock promoted apical ATP secretion and increased intracellular Ca(2+). While apyrase, an ATP scavenger, did not inhibit the hypotonic shock current response, W7 a calmodulin antagonist completely prevented the hypotonic current rise. These results indicate that a basolateral Cl(-) influx as well as Ca(2+)/calmodulin, but not ATP, are involved in the acute transepithelial current rise elicited by hypotonic shock.
肺泡上皮细胞通过上皮钠通道（ENaC）参与钠（Na+）吸收，这是维持呼吸上皮衬里适当液体体积和肺水肿清除的重要过程。在这里，我们研究了 20%的低渗冲击如何调节这些细胞中的离子电流。从大鼠肺中分离的极化肺泡上皮细胞在可渗透滤器上培养，并记录其电生理特性。20%的双侧低渗冲击立即引起总跨上皮电流增加 52%，并使 ENaC 介导的阿米洛利敏感电流增加 67%。阿米洛利预处理降低了低渗冲击后的电流上升，表明 ENaC 电流参与了这种反应。由于 Cl-转运受低渗冲击调节，因此还评估了其对基础和低渗诱导的跨上皮电流的贡献。顶端 NPPB，一种广泛的 Cl-通道抑制剂和基底外侧 DIOA，一种钾氯共转运体（KCC）抑制剂，降低了总电流和 ENaC 电流，表明细胞间 Cl-转运在该过程中起主要作用。在低渗冲击期间，由 NPPB 部分抑制的基底外侧 Cl-内流对于低渗诱导的电流上升是必需的。低渗冲击促进顶端 ATP 分泌并增加细胞内 Ca2+。虽然 ATP 清除剂 apyrase 没有抑制低渗冲击电流反应，但钙调蛋白拮抗剂 W7 完全阻止了低渗电流上升。这些结果表明，基底外侧 Cl-内流以及 Ca2+/钙调蛋白，但不是 ATP，参与了低渗冲击引起的急性跨上皮电流上升。
