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Albumin absorption by canine bronchial epithelium
L G Johnson1, P W Cheng, R C Boucher
1Department of Medicine, School of Medicine, University of North Carolina, Chapel Hill 27599.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 1, 1989
Summary
Bronchial epithelia actively absorb albumin through a low-affinity process, contributing to lower albumin concentrations in airway surface liquid compared to plasma. This absorption mechanism is temperature-dependent and saturable.
Area of Science:
- Pulmonary Physiology
- Epithelial Transport
Background:
- Airway surface liquid (ASL) has lower albumin concentrations than plasma.
- Mechanisms generating albumin gradients across airway epithelia are not fully understood.
Purpose of the Study:
- Investigate active albumin absorption by bronchial epithelia.
- Determine if bronchial epithelia contribute to ASL albumin homeostasis.
Main Methods:
- Canine bronchi mounted in Ussing chambers.
- Measured 14C-albumin permeability in mucosal-to-submucosal and submucosal-to-mucosal directions.
- Assessed [3H]inulin transport and analyzed albumin fragments via gel filtration chromatography.
Main Results:
- Significantly higher albumin permeability in the absorptive (M-S) direction compared to the S-M direction.
- No asymmetry in fluid phase marker ([3H]inulin) transport observed.
- Net albumin absorption inhibited by low temperature and saturated at high unlabeled albumin concentrations.
- Majority of radiolabel in submucosal solution comprised albumin fragments, but fragments themselves were not transported.
Conclusions:
- Bronchial epithelia actively absorb albumin via a saturable, low-affinity process.
- This active absorption mechanism likely contributes to maintaining low albumin concentrations in airway secretions.
- Albumin fragments do not account for the observed net absorption.