Localized Acid Instillation by a Wedged‐Catheter Method Reveals a Role for Vascular Gap Junctions in Spatial Expansion of Acid Injury

Abstract

Acid aspiration is a major cause of acute lung injury. However, the mechanisms that underlie this spatial expansion of the injury remain undefined. In current animal models of acid injury, intratracheal acid instillation replicates the lung injury. However intratracheal instillation causes a global effect, precluding studies of how the injury spreads. Here, we report an airway catheter-based method for localized acid delivery in the isolated blood-perfused rat lung. We co-instilled hydrochloric acid with evans blue through the catheter into one lung and determined blood-free extravascular lung water in tissue samples from regions that either received, or did not receive the instilled acid. Tissue samples from the non-catheterized contralateral lung were used as controls. Lung water increased both in the regions that received acid, as well as in adjacent regions that did not. Pre-treating the lung with vascular infusions of the gap junctional blocker, glycerrhetinic acid, blunted the acid-induced lung water increase at the adjacent regions. These findings indicate that endothelial gap junction communication causes spread of lung injury from regions that were directly acid injured, to adjacent sites that did not directly receive acid. Our new method for establishing localized acid injury provides evidence for a novel role for vascular gap junctions in the spatial expansion of acid injury.

Endothelial connexin43 mediates acid-induced increases in pulmonary microvascular permeability

“…At the concentration reported to block endothelial Cx43 channels (5), GA blocked the acid-induced responses in vessels located more than 200 m from the acidinstilled site. In a recent report, GA pretreatment did not inhibit acid-induced lung water increases at the site of direct injury (20). The present findings that vascular GA significantly blunted acid-induced reduction in normalized fluorescence only in microvessels located outside the acid-treated region are in agreement with these reported data.…”

“…Since the average size of the acid-instilled region was in the 500-m range, the responses appear to spread approximately three times this size. These data are similar to that reported recently, wherein lung water increases spread up to 3 cm in response to acid instillation in a 1-cmsized region (20).…”

“…This suggests that the acid instillation initiated responses even in microvessels that did not abut treated alveoli. These data are similar to recent findings (20) in which intrabronchial instillation of acid in a small lung region increased lung water at sites more than 2 cm away from the acid-instilled region. These remote increases were blocked by inhibiting interendothelial gap junctional communication.…”

“…To inhibit endothelial gap junction communication, the inhibitors were infused into microvessels prior to alveolar acid instillation. The pretreatment duration for GA was 10 min, whereas that for Gap27 was 1 h, as reported previously (3,5,20,21). Since the inhibitory effect of Gap27 is lost when the peptide is washed off (21), Gap27 infusion was maintained even after acid instillation, by mixing it with FDx20.…”

“…Endothelial connexin43 (Cx43)-containing gap junctions mediate the spatial spread of proinflammatory responses in pulmonary microvessels (21). It was reported recently that intrabronchial instillation of acid into a small region of the lung induced spatially extensive lung injury, as determined by increases in lung water (20). Lung water increases at the remote sites, but not at the acid-instilled region, were blunted by pretreating microvessels with the gap junctional blocker glycyrrhetinic acid.…”