Endothelial connexin43 mediates acid-induced increases in pulmonary microvascular permeability

Abstract

Parthasarathi K. Endothelial connexin43 mediates acid-induced increases in pulmonary microvascular permeability. Am J Physiol Lung Cell Mol Physiol 303: L33-L42, 2012. First published May 4, 2012 doi:10.1152/ajplung.00219.2011.-Acid aspiration, a common cause of acute lung injury, leads to alveolar edema. Increase in lung vascular permeability underlies this pathology. To define mechanisms, isolated rat lungs were perfused with autologous blood. Hydrochloric acid and rhodamine-dextran 70 kDa (RDx70) were coinstilled into an alveolus by micropuncture. RDx70 fluorescence was used to establish the spatial distribution of acid. Subsequently, FITCdextran 20 kDa (FDx20) was infused into microvessels for 60 min followed by a 10-min HEPES-buffered saline wash. During the infusion, FITC fluorescence changes were recorded to quantify the ratio of peak to postwash fluorescence. The ratio, termed normalized fluorescence, was low for acid compared with buffer instillation both in microvessels abutting acid-treated alveoli and those located more than 700 m away. In contrast, the normalized fluorescence was similar to buffer controls when a higher molecular weight tracer (FITC-dextran 70 kDa) was infused instead of FDx20, suggesting that normalized FDx20 fluorescence faithfully represented microvascular permeability. Inhibiting endothelial connexin43 (Cx43) gap junction communication with Gap27 blunted the acid-induced reduction in normalized fluorescence, although scrambled Gap27 did not have any effect. The blunting was evident not only in microvessels away from the site of injury, but also in those abutting directly injured alveoli. Thus the new fluorescence-based method reveals that acid increases microvascular permeability both at acid-instilled and away sites. Inhibiting endothelial Cx43 blocked the permeability increase even at the direct injury sites. These data indicate for the first time that Cx43-dependent mechanisms mediate acid-induced increases in microvascular permeability. Cx43 may be a therapeutic target in acid injury. acid injury; blood-perfused lung; FITC-dextran; fluorescence; gap junctions

Gap Junction Protein Connexin43 Exacerbates Lung Vascular Permeability

“…Recent reports showing attenuation of acid- and thrombin-induced permeability in the lung microvasculature by Cx43-blocking peptides support this model [40], [41]. However, in those whole animal studies, other cell types (e.g., pulmonary epithelial cells) likely also contribute to permeability.…”

Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction

“…For example, Cx43 has been shown to mediate interendothelial Ca 2ϩ movement that upregulates the leukocyte adhesion receptor, P-selectin, thereby contributing to propagation of inflammation (184). Moreover, inhibition of Cx43 with the peptide inhibitor Gap27 prevents increases in endothelial permeability after focal micropuncture instillation of acid into alveoli at sites of both acid-instilled and acid-free regions, confirming the important role for this gap junctional channel in alveolar endothelial-endothelial cell interaction and injury expansion (183).…”

Novel regulators of endothelial barrier function

“…Cx43-mediated GJs form conduits for the spread of proinflammatory signals in the lung capillary bed (110). Parthasarthi (109) showed that in the lung microvasculature connexins transduce alveolar-capillary damage to distant sites as well as at the injury site. Using a micropuncture technique to locally instill hydrochloric acid along with rhodamine-dextran 70 kDa (RDx70) and FITC-dextran 20 kDa (FDx20) he showed that acid decreased the peak postwash fluorescence of FDx20 both in microvessels at the infusion site of alveoli and also those located Ͼ700 m away.…”