Electron microscopic evidence for a glomerular periendothelial layer of hydrophilic material.
Research field:Kidney physiology
Authors:Hjalmarsson C, Johansson BR, Haraldsson B
Address of presenting
author:		Department of Physiology
Göteborg University
Box 432
SE-405 30 Göteborg
Sweden
E-mail:clara.hjalmarsson@fysiologi.gu.se
Phone:+46 31 773 3357
Fax:+46 31 773 3512
Text of abstract Introduction
The general concept regarding glomerular permeability is that the podocytes and the basement membrane are the main components governing the filtration of water and solutes. The fenestrated endothelium has been more or less neglected. Recent data from different vascular beds suggest however that the layer of endothelial glycocalyx that lines the endothelial cells could be an important component of the capillary barrier. Many studies have used cationic dyes to reveal a thick cell coat (200-300nm) filling also the fenestrae. However, such cationic dyes can per se alter the morphology. Another approach to visualize a negatively charged polysaccharide-rich gel along the endothelial surface would be to label the blood plasma with a tracer expected to have a low access to the gel. To this end, we administered a lipid solution intravenously.

Methods
The present study was performed in Sprague-Dawley female rats. Anesthesia was induced and maintained with Pentobarbitone. After laparatomy, the left kidney was exposed and Intralipid was administered (bolus) into the caval vein. The renal pedicle was clamped and the kidney was fixed in situ by subcapsular injection of Karnovsky fixative. Intralipid 20%, with a mean droplet diameter of 0.25 ± 0.04mm was used as ‘tracer’. The presence of an ‘exclusion zone’ was studied in rat glomerular capillaries using peritubular capillaries as controls. All pictures were scanned and processed in a computer. The luminal area was divided virtually in two zones: a central and a periendothelial zone, the latter being 200 nm wide. 2346 particles were counted in 96 glomerular capillaries from 6 rats.

Results
The density of the Intralipid particles was significantly lower in the peripheral than in the central area of the glomerular capillaries, 0.046 ± 0.010 and 0.428 ± 0.067 particles/mm2 respectively, giving a peripheral/central density of 11%, p<0.001. Data obtained from 21 peritubular capillaries showed a uniform distribution of Intralipid particles in the two zones, 0.306 ± 0.130 (central) vs. 0.312 ± 0.069 (peripheral) particles/mm2.

Conclusions
Thus, we report the presence of an “exclusion” zone with periendothelial localization and an average thickness of 200 nm. We suggest that this zone is occupied by endothelial glycocalyx acting as a negatively charged ion-exchange gel.

References

Keywords:Intralipid, endothelium, glomerular, capillary, permeability

Created 20000-05-31