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Faster aqueous than phospholipid exocytosis during alveolar surfactant secretion
Author(s) -
Islam Mohammad Naimul,
Das Shonit,
Perlman Carrie E,
Lindert Jens,
Bhattacharya Jahar
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.931.5
Subject(s) - phospholipid , exocytosis , lamellar granule , pulmonary surfactant , secretion , fluorescence microscope , chemistry , biophysics , bodipy , aqueous solution , alveolar cells , fluorescence , microbiology and biotechnology , biology , biochemistry , lung , medicine , membrane , physics , quantum mechanics
Lamellar bodies (LB) of alveolar type 2 cells consist of an aqueous phase that surrounds a phase containing surfactant protein B (SPB) in complex with surfactant phospholipids. Surfactant secretion entails exocytosis of the aqueous and the SPB‐phospholipid phases. To determine the extent to which these phases are secreted differently, we imaged by live confocal microscopy, single alveoli of isolated, blood‐perfused rat lungs held at alveolar pressure (Palv) of 5 cmH 2 O. Then, by alveolar micropuncture, we co‐loaded type 2 cells with purified, fluorescent SPB (BODIPY‐SPB) and the LB‐localizing marker, LysoTracker Red (LTR) to mark respectively, the phospholipid and the aqueous phases in LB. In single alveoli, type 2 cells were revealed by the high fluorescence of both BODIPY‐SPB and LTR. Thirty minutes after a single 15‐s inflation to Palv of 15 cmH 2 O, type 2 cell fluorescence decreased for BODIPY‐SPB by 46.6 ± 2.9% of initial (mean ± SE; n=4), but markedly more for LTR, namely by 72.5 ± 4.5% of initial (p<0.05). Thus, the fluorescence decay rate for BODIPY‐SPB was half that for LTR (P<.05). We interpret that during surfactant secretion, phospholipid versus aqueous secretion rates differ markedly. The difference might be attributable to differences in phase mobility resulting from the geometry of the LB exocytosis pathway (support: HL64896).