NO‐regulated negative feedback loop protects lung endothelial barrier function in hydrostatic stress

Abstract

Hydrostatic stress in lung capillaries increases endothelial Ca2+ concentration ([Ca2+]i), thereby elevating capillary filtration coefficient (Kfc) and promoting NO synthesis. By in situ fluorescence imaging and measurement of Kfc, we studied the role of endothelial NO in the regulation of microvascular permeability in the isolated rat lung. Means ± SEM, ∗ p<0.05 vs. baseline, # p<0.05 vs. control. In control lungs, PLA elevation increased endothelial [Ca2+]i from 100±4 to 147±5 nM∗, NO production to 239±18 %∗ (of baseline), and Kfc from 0.4±0.1 to 2.6±0.7 ml·min−1·cmH2O−1·100g−1∗(unit). NO synthase inhibition (L-NAME) amplified the pressure-induced [Ca2+]i and Kfc responses to 194±7 nM# and 3.7±0.3 unit# whereas the exogenous NO donor GSNO attenuated both responses (125±5 nM# and 1.2±0.4 unit#). Endothelial [Ca2+]i response and Kfc were also augmented to 232±20 nM# and 5.5±0.4 unit# by the soluble guanylate cyclase (sGC) inhibitor ODQ. Conversely, both the sGC activator Bay 41-2272 and the cGMP analogue 8Br-cGMP abrogated the pressure-elicited endothelial [Ca2+]i response to 108±5 nM# and 103±1 nM#, NO production to 101±3 %# and 127±9 %#, and Kfc to 1.2±0.2 unit#. Pressure-induced NO formation may constitute a negative feedback loop limiting the endothelial [Ca2+]i response and thus, protecting the lung microvascular barrier by cGMP-dependent inhibition of pressure-induced Ca2+ transients.