Lung surfactant secretion by interalveolar Ca2+ signaling.
Although clusters of alveoli form the acinus, which is the most distal respiratory unit, it is not known whether interalveolar communication coordinates acinar surfactant secretion. To address this, we applied real-time digital imaging in conjunction with photo-excited Ca2+ uncaging in intact alveoli of the isolated, blood-perfused rat lung. We loaded alveolar cells with the Ca2+ cage o-nitrophenyl EGTA-AM (NP-EGTA-AM) together with the fluorophores, fluo 4, or LysoTracker green (LTG) to determine, respectively, the cytosolic Ca2+ concentration ([Ca2+]cyt) or type 2 cell secretion. To uncage Ca2+ from NP-EGTA, we exposed a region in a selected alveolus to high-intensity UV illumination. As a result, fluo 4 fluorescence increased, whereas LTG fluorescence decreased, in the photo-targeted region, indicating that uncaging both increased [Ca2+]cyt and induced secretion. Concomitantly, [Ca2+]cyt increases conducted from the uncaging site induced type 2 cell secretion in both the selected alveolus as well as in neighboring alveoli, indicating the presence of interalveolar communication. These conducted responses were inhibited by pretreating alveoli with the connexin43 (Cx43)-inhibiting peptides gap 26 and gap 27. However, although the conducted [Ca2+]cyt increase diminished with distance from the uncaging site, type 2 cell secretion rates were similar at all locations. We conclude that Cx43-dependent, interalveolar Ca2+ signals regulate type 2 cell secretion in adjacent alveoli. Such interalveolar communication might facilitate acinar coordination of alveolar function.
Ichimura
Hideo
H
Lung Biology Laboratory, Department of Physiology and Cellular Biophysics, College of Physicians and Surgeons, Columbia University, St. Luke's-Roosevelt Hospital Center, New York, NY 10019, USA.
Parthasarathi
Kaushik
K
Lindert
Jens
J
Bhattacharya
Jahar
J
D000814:Aniline Compounds; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D017630:Connexins / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D005456:Fluorescent Dyes; D017629:Gap Junctions / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D009842:Oligopeptides; D010455:Peptides / Q000494:pharmacology; D011650:Pulmonary Alveoli / Q000187:drug effects / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014966:Xanthenes
D000814:Aniline Compounds; D017630:Connexins; C409648:Fluo 4; D005456:Fluorescent Dyes; C514423:Gap 26 peptide; D009842:Oligopeptides; D010455:Peptides; D011663:Pulmonary Surfactants; D014966:Xanthenes; C455880:gap 27 peptide; C508966:o-nitrophenylegtazic acid acetoxymethyl ester; D004533:Egtazic Acid; D002118:Calcium