Plasmalemmal vesicles function as transcytotic carriers for small
proteins in the continuous endothelium.
Predescu, Sanda A., Dan N. Predescu, and George E. Palade.
Division of Cellular and Molecular Medicine, University of
California, San Diego, California, 92122 - 0651
APStracts 3:0411H, 1996.
We investigated the location and the structural identity of the small
pore system, postulated by the pore theory of capillary permeability,
using a murine heart perfusion system and small protein molecules as
preferential probes for the small pores. Dinitrophenylated proteins
were perfused in situ, in the absence and in the presence of N
-ethylmaleimide, a reagent known to interfere with membrane fusion of
vesicular carriers with their target membranes. The exit pathways of
the tracers from vascular lumina to the interstitia were followed by
immunoelectron microscopy and by tissue fractionation-biochemistry,
to quantitate their transport and to estimate the extent of transport
inhibition by NEM. After 5 min perfusion, all tracers used, were
found essentially restricted to plasmalemmal vesicles within the
endothelium and NEM inhibited their transport by 80% to 85%. The
transport of [14C]-inulin and [14C]-sucrose, assumed to follow the
paracellular pathway, was marginally affected by NEM. These findings
indicate that plasmalemmal vesicles function as structural
equivalents of the small pore system, for molecules larger than 2 nm
diameter.
Received 26 April 1996; accepted in final form 6 September 1996.
APS Manuscript Number H371-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996