Background: Surfactant components can be recycled (= reuptake→ resecretion) by alveolar type II cells. Surfactant protein A is involved in this process.
Question: Elucidation of the kinetics and mechanisms of this recycling process.
Methods: Surfactant resecretion assays in freshly isolated rat type II pneumocytes. Endocytosis and resecretion of surfactant-like liposomes labeled in the phospholipid surfactant protein A components.
Results: Surfactant components taken up by SP-A-mediated endocytosis are rapidly resecreted by type II cells (cycle time ≤ 15 min) in contrast to the much slower resecretion after liposome uptake in the absence of SP-A (p<0.05). It is energy dependent and inhibitable by extracellular SP-A but not by extracellular lipid. Surfactant lipids internalized by SP-A-mediated endocytosis are resecreted intact(96±0.2%) in contrast to lipids taken up in the absence of SP-A (≈ 50% degradation/resynthesis).
Conclusions: These studies will lead to a better understanding of how extracellular surfactant is incorporated into the endogenous surfactant pools. This may be useful to improve therapeutic strategies of surfactant substitution.
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Stevens, P., Zastrow, S., Sieger, D. et al. Kinetics of Surfactantprotein A-specific surfactantresecretion by type II pneumocytes. Pediatr Res 42, 415 (1997). https://doi.org/10.1203/00006450-199709000-00199
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DOI: https://doi.org/10.1203/00006450-199709000-00199