The sp-a-binding protein bp55 is involved in surfactant endocytosis
by type ii pneumocytes.
Wissel, Heide, Alfred C. Looman, Ingo Fritzsche, Bernd R[umlaut]ustow,
and Paul A. Stevens.
Dept. of Neonatology, University Children's Hospital,
Charit[acute]e, Humboldt University Berlin, Berlin, Germany
APStracts 3:0091L, 1996.
The mechanism of SP-A-mediated lipid uptake by rat type II pneumocytes
was investigated. In the absence of SP-A, freshly isolated type II
pneumocytes actively take up very little if any liposomes. Most of
the increase with time is independent of energy or temperature but
most likely due to spontaneous exchange of labeled lipids between
liposomes and cell membranes. With 5 [mu]g/ml SP-A, type II cells
actively take up liposomes (244 pmol DPPC/h/106 cells). The effect of
SP-A on uptake is temperature-dependent and can be abolished by ATP
-depletion of the cells. Coincubation with an autoantiidiotypic
antibody against the SP-A-binding protein bp55 on the cell membrane
of type II pneumocytes inhibits SP-A-mediated lipid uptake by type II
cells. With increasing amounts of extracellular SP-A present,
increasing amounts of liposomes are taken up and directed towards a
non-degrading compartment.
We suggest that SP-A-mediated surfactant lipid uptake is a receptor
-mediated endocytotic process involving bp55.
Received 7 December 1995; accepted in final form 10 May 1996.
APS Manuscript Number L357-5.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96