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Related Experiment Videos

Tripeptide transport in rat lung

P A Helliwell1, D Meredith, C A Boyd

  • 1Department of Biology, University of York, UK.

Biochimica Et Biophysica Acta
|March 23, 1994
PubMed
Summary

The rat lung transports L-alanyl-D-phenylalanyl-L-alanine intact, but also hydrolyzes 47% of it into D-phenylalanine during passage. This tripeptide transport occurs via type II pneumocyte membrane vesicles.

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Area of Science:

  • Pulmonary physiology
  • Molecular transport mechanisms
  • Biochemistry

Background:

  • The lung epithelium plays a crucial role in xenobiotic and endogenous compound transport.
  • Understanding peptide transport across the alveolar epithelium is vital for drug delivery and understanding lung function.
  • Type II pneumocytes form the primary barrier of the alveolar epithelium.

Purpose of the Study:

  • To investigate the transport and hydrolysis of the tripeptide L-alanyl-D-phenylalanyl-L-alanine across the rat lung epithelium.
  • To characterize the role of type II pneumocyte brush border membrane vesicles in tripeptide uptake.
  • To compare the transport of stereoisomers of the tripeptide and related dipeptides.

Main Methods:

  • In situ vascular perfusion of rat lungs.

Related Experiment Videos

  • Preparation and functional assay of brush border membrane vesicles from rat type II pneumocytes.
  • Uptake studies using radiolabeled tripeptides and dipeptides.
  • Analysis of perfusate and vesicle contents using chromatography and mass spectrometry.

    • Main Results:

    • The tripeptide L-alanyl-D-phenylalanyl-L-alanine was transported intact from the alveolar lumen to the vascular perfusate at 25.1 nmol/min/g dry weight.
    • 47% of the absorbed tripeptide was hydrolyzed, releasing D-phenylalanine into the perfusate.
    • Apical membrane vesicles from type II pneumocytes showed rapid uptake of L-alanyl-D-phenylalanyl-L-alanine, which was abolished by Triton treatment.
    • Stereoisomeric tripeptide D-alanyl-L-phenylalanyl-D-alanine showed slower uptake by vesicles.
    • D-phenylalanyl-L-alanine appeared faster in perfusate than the intact tripeptide, while D-phenylalanyl-D-alanine transport was slow and not hydrolyzed.

    Conclusions:

    • The rat lung epithelium actively transports the tripeptide L-alanyl-D-phenylalanyl-L-alanine.
    • Hydrolysis of the tripeptide occurs during its passage across the alveolar epithelial barrier.
    • Type II pneumocyte apical membrane vesicles are involved in the uptake of this tripeptide.
    • Stereochemistry significantly influences the transport and hydrolysis rates of these peptides across the lung epithelium.