Endothelin-1 impairs alveolar epithelial function via endothelial ET _B receptor

Rationale: Endothelin-1 (ET-1) is increased in patients with high-altitude pulmonary edema and acute respiratory distress syndrome, and these patients have decreased alveolar fluid reabsorption (AFR). Objectives: To determine whether ET-1 impairs AFR via activation of endothelial cells and nitric oxide (NO) generation. Methods: Isolated perfused rat lung, transgenic rats deficient in ET_B receptors, coincubation of lung human microvascular endothelial cells (HMVEC-L) with rat alveolar epithelial type II cells or A549 cells, ouabain-sensitive ⁸⁶Rb⁺ uptake. Measurements and Main Results: The ET-1-induced decrease in AFR was prevented by blocking the endothelin receptor ET_B, but not ETA. Endothelial-epithelial cell interaction is required, as direct exposure of alveolar epithelial cells (AECs) to ET-1 did not affect Na,K-ATPase function or protein abundance at the plasma membrane, whereas coincubation of HMVEC-L and AECs with ET-1 decreased Na,K-ATPase activity and protein abundance at the plasma membrane. Exposing transgenic rats deficient in ET_B receptors in the pulmonary vasculature (ET-B^-/-) to ET-1 did not decrease AFR or Na,K-ATPase protein abundance at the plasma membrane of AECs. Exposing HMVEC-L to ET-1 led to increased NO, and the ET-1-induced down-regulation of Na,K-ATPase was prevented by the NO synthase inhibitor L-NAME, but not by a guanylate cyclase inhibitor. Conclusions: We provide the first evidence that ET-1, via an endothelial-epithelial interaction, leads to decreased AFR by a mechanism involving activation of endothelial ET_B receptors and NO generation leading to alveolar epithelial Na,K-ATPase down-regulation in a cGMP-independent manner.