Location of focal silver staining at endothelial gaps in inflamed
venules examined by scanning electron microscopy.
Hirata, Akira, Peter Baluk, Takashi Fujiwara, and Donald M. McDonald.
Cardiovascular Research Institute and Department of Anatomy,
University of California, San Francisco, CA 94143, Present address:
Department of Anatomy and Ophthalmology, Kumamoto University School
of Medicine, Kumamoto 860, JAPAN, Present address: Laboratory Animal
Center, Ehime University School of Medicine, Shigenobu, Ehime 791-02,
JAPAN
APStracts 2:0077L, 1995.
The century-old histological technique of silver nitrate staining has
proven to be extremely useful for visualizing endothelial cell
borders and localizing endothelial gaps, but the significance of the
staining is still not fully understood. To gain some insight into
what silver nitrate stains, we developed a method that enabled us to
use scanning electron microscopy with backscattered and secondary
electron imaging to examine silver staining at endothelial cell
borders of venules of the rat tracheal mucosa. We found that in
normal venules, silver lines followed the smooth contour of cell
borders. However, 1 min after endothelial permeability was increased
by substance P, cell borders were irregular and displaced from the
silver lines by as much as 4.3 [mu]m, and the lines were accompanied
by three types of silver deposits. Most common (46% of total) were
annulus-shaped silver deposits that surrounded endothelial gaps.
These deposits averaged 1.5 [mu]m in width, were positioned
symmetrically across cell borders, and were located at a depth of 0.3
[mu]m beneath the luminal surface. Many endothelial gaps were
partitioned into multiple pores (mean, 2.4) by finger-like processes
of endothelial cells. Surprisingly, the gaps occupied only 5.4% of
the total area of the silver deposits and constituted 0.15% of the
luminal surface of the leaky postcapillary venules. A second type of
silver deposit ( 19% of total) was positioned asymmetrically with
respect to the cell border and marked sites where endothelial cell
margins still overlapped but appeared to be vertically separated by
obliquely-oriented gaps. A third type marked gaps at 3-cell
junctions; these were no more abundant than deposits elsewhere around
the cell perimeter, suggesting that 3-cell junctions were not
unusually leaky sites. We conclude that silver nitrate marks
endothelial cell borders and outlines endothelial cell gaps by
staining an element of intercellular junctions. The annular shape of
many silver deposits around gaps suggests that junctional elements in
the apposing cells are separated during gap formation but are still
present at the gap perimeter.
Received 14 November 1994; accepted in final form 1 May 1995.
APS Manuscript Number L326-4.
Article publication pending Am. J. Physiol. (Lung Cell. Mol.
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 9 May 1995.