Hypoxic pulmonary vasoconstriction requires connexin 40–mediated endothelial signal conduction
Liming Wang, … , Hermann Kuppe, Wolfgang M. Kuebler
Liming Wang, … , Hermann Kuppe, Wolfgang M. Kuebler
Published October 24, 2012
Citation Information: J Clin Invest. 2012;122(11):4218-4230. https://doi.org/10.1172/JCI59176.
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Research Article

Hypoxic pulmonary vasoconstriction requires connexin 40–mediated endothelial signal conduction

Abstract

Hypoxic pulmonary vasoconstriction (HPV) is a physiological mechanism by which pulmonary arteries constrict in hypoxic lung areas in order to redirect blood flow to areas with greater oxygen supply. Both oxygen sensing and the contractile response are thought to be intrinsic to pulmonary arterial smooth muscle cells. Here we speculated that the ideal site for oxygen sensing might instead be at the alveolocapillary level, with subsequent retrograde propagation to upstream arterioles via connexin 40 (Cx40) endothelial gap junctions. HPV was largely attenuated by Cx40-specific and nonspecific gap junction uncouplers in the lungs of wild-type mice and in lungs from mice lacking Cx40 (Cx40–/–). In vivo, hypoxemia was more severe in Cx40–/– mice than in wild-type mice. Real-time fluorescence imaging revealed that hypoxia caused endothelial membrane depolarization in alveolar capillaries that propagated to upstream arterioles in wild-type, but not Cx40–/–, mice. Transformation of endothelial depolarization into vasoconstriction involved endothelial voltage-dependent α1G subtype Ca2+ channels, cytosolic phospholipase A2, and epoxyeicosatrienoic acids. Based on these data, we propose that HPV originates at the alveolocapillary level, from which the hypoxic signal is propagated as endothelial membrane depolarization to upstream arterioles in a Cx40-dependent manner.

Authors

Liming Wang, Jun Yin, Hannah T. Nickles, Hannes Ranke, Arata Tabuchi, Julia Hoffmann, Christoph Tabeling, Eduardo Barbosa-Sicard, Marc Chanson, Brenda R. Kwak, Hee-Sup Shin, Songwei Wu, Brant E. Isakson, Martin Witzenrath, Cor de Wit, Ingrid Fleming, Hermann Kuppe, Wolfgang M. Kuebler

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Figure 6

Endothelial membrane depolarization.

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Endothelial membrane depolarization. (A) Representative images (of 5 rep...
(A) Representative images (of 5 replicates) showing endothelial di-8-ANEPPS fluorescence in capillaries and arterioles of Cx40+/+ and Cx40–/– lungs at normoxia (21% O2) and after 10 minutes of hypoxia (1% O2). Arteriolar vessel margins are shown by dotted lines, and representative capillary and arteriolar endothelium are denoted by circles and squares, respectively. Scale bar: 50 μm. (B) Representative tracings (of 5 replicates) of di-8-ANEPPS fluorescence. Hypoxia-induced ΔEm in capillaries preceded arteriole response. Group data (n = 5 lungs each) showing (C) comparable baseline endothelial di-8-ANEPPS fluorescence (reflecting Em) and (D) hypoxia-induced increases in endothelial di-8-ANEPPS fluorescence (reflecting ΔEm) in capillaries and arterioles of Cx40+/+ and Cx40–/– lungs. *P < 0.05 vs. capillaries; #P < 0.05 vs. Cx40+/+. (E) Calibration of endothelial di-8-ANEPPS fluorescence by lung perfusion with different [K+]. n = 3 lungs each. (F) Group data (n = 5 lungs each) showing ΔPAP in response to hypoxia (1% O2) or Ang II (1 μg bolus) in isolated Cx40+/+ lungs perfused with 5.9 or 20 mM [K+]. *P < 0.05 vs. 5.9 mM. (G) Representative Western blots showing Kv1.5 and Kv2.1 expression in freshly isolated pulmonary endothelial cells; whole lung homogenate, rat PASMCs, and HUVECs served as controls. (H) Group data (n = 5 lungs each) showing endothelial ΔEm in capillaries and arterioles of Cx40+/+ and Cx40–/– lungs in response to 10 mM 4-aminopyridine. No significant differences.