Dipeptide transport characteristics of the apical membrane of rat
lung type ii pneumocytes.
Boyd, D. Meredith C. A. R.
DEPARTMENT OF HUMAN ANATOMY, SOUTH PARKS ROAD, OXFORD, OX1 3QX, UK,
PRESENT ADDRESS: BRIGHAM & WOMEN'S HOSPITAL, HARVARD MEDICAL
SCHOOL, 75 FRANCIS STREET, BOSTON, MASSACHUSETTS 02115, USA
APStracts 2:0051L, 1995.
The transport of a hydrolysis-resistant dipeptide, D-Phe-L-Ala, has
been studied by high performance liquid chromatography in rat lung
epithelial cells and apical membrane vesicles. Time-dependent uptake
of D-Phe-L-Ala into isolated type II pneumocytes was shown. Uptake
was saturable, and Michaelis-Menten kinetics were fitted to the data
and gave an apparent Km of 3.4mM, and a Vmax of 7.0 nmoles (mg
protein)-1 (minute)-1. However, known peptide transport inhibitors
unexpectedly increased intracellelar D-Phe-L-Ala concentration when
initial rates of peptide uptake were studied. Apical (brush-border)
membrane vesicles prepared from rat lung also showed time- and
concentration-dependent influx of D-Phe-L-Ala (apparent Km 2.0mM,
Vmax 0.53 nmoles (mg protein)-1 (minute)-1. Influx of this neutral
dipeptide into the vesicles was shown to be both electrogenic and
stimulated by an inwardly-directed proton gradient. Influx was
inhibitable by mercuric chloride, and by the amino-acid residue
modifying compounds N-acetylimidazole and diethylpyrocarbonate. These
findings strongly suggest the presence of a proton-coupled peptide
transport protein in the apical surface of the type II cell. This
transporter may play a role in lung homeostasis.
Received 24 October 1994; accepted in final form 30 March 1995.
APS Manuscript Number L304-4.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 April 1995.