[Ca(2+)](i) oscillations regulate type II cell exocytosis in the pulmonary alveolus.
Pulmonary surfactant, a critical determinant of alveolar stability, is secreted by alveolar type II cells by exocytosis of lamellar bodies (LBs). To determine exocytosis mechanisms in situ, we imaged single alveolar cells from the isolated blood-perfused rat lung. We quantified cytosolic Ca(2+) concentration ([Ca(2+)](i)) by the fura 2 method and LB exocytosis as the loss of cell fluorescence of LysoTracker Green. We identified alveolar cell type by immunofluorescence in situ. A 15-s lung expansion induced synchronous [Ca(2+)](i) oscillations in all alveolar cells and LB exocytosis in type II cells. The exocytosis rate correlated with the frequency of [Ca(2+)](i) oscillations. Fluorescence of the lipidophilic dye FM1-43 indicated multiple exocytosis sites per cell. Intracellular Ca(2+) chelation and gap junctional inhibition each blocked [Ca(2+)](i) oscillations and exocytosis in type II cells. We demonstrated the feasibility of real-time quantifications in alveolar cells in situ. We conclude that in lung expansion, type II cell exocytosis is modulated by the frequency of intercellularly communicated [Ca(2+)](i) oscillations that are likely to be initiated in type I cells. Thus during lung inflation, type I cells may act as alveolar mechanotransducers that regulate type II cell secretion.
Ashino
Y
Y
Department of Medicine, College of Physicians and Surgeons and St. Luke's Roosevelt Hospital Center, Columbia University, New York, New York 10019, USA.
Ying
X
X
Dobbs
L G
LG
Bhattacharya
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D008168:Lung / Q000502:physiology; D008856:Microscopy, Fluorescence; D009994:Osmolar Concentration; D010812:Physical Stimulation; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D005456:Fluorescent Dyes; D002118:Calcium; D016257:Fura-2