Leakiness of the endothelial bed is attributed to the over-perfusion of the pulmonary bed, which leads to high altitude
pulmonary edema (HAPE). Inhalation of
nitric oxide has been successfully employed to treat HAPE patients. We hypothesize that
nitric oxide intervenes in the permeability of the pulmonary macrovascular endothelial bed to rectify the leaky bed under
hypoxia. Our present work explores the underlying mechanism of '
hypoxia-mediated' endothelial malfunction by using human umbilical cord-derived immortalized endothelial cells, ECV-304, and bovine pulmonary artery primary endothelial cells. The leakiness of the endothelial monolayer was increased by two-fold under
hypoxia in comparison to cells under normoxia, while optical tweezers-based tethering assays reported a higher membrane tension of endothelial cells under
hypoxia.
Phalloidin staining demonstrated depolymerization of
F-actin stress fibers and highly polarized
F-actin patterns in endothelial cells under
hypoxia.
Nitric oxide, 8-Br-cGMP and
sildenafil citrate (
phosphodiesterase type 5 inhibitor) led to recovery from
hypoxia-induced leakiness of the endothelial monolayers. Results of the present study also suggest that '
hypoxia-induced' cytoskeletal rearrangements and membrane leakiness are associated with the low
nitric oxide availability under
hypoxia. We conclude that
nitric oxide-based recovery of
hypoxia-induced leakiness of endothelial cells is a cyclic
guanosine monophosphate (cGMP)-dependent phenomenon.