The present study served to evaluate extravasation of albumin across the microvascular endothelium of the chick chorioallantoic membrane (CAM) during the establishment of endothelial barrier functions (days 4.5 to 6.0), during a rapid phase of normigenesis (day 10), and after initiation of endothelial cytodifferentiation (day 14). CAM preparations in shell-less cultures were evaluated by intravital fluorescence confocal microscopy and videodensitometry after microinjections of chicken serum albumin (CSA) conjugated to Fluorescein isothiocyanate (FITC) (1% in Avian Ringers). At each observed temporal stage, FITC-CSA extravasation from the CAM pre-capillaries, capillaries, and post-capillaries was uniformly negligible. Since the endothelial glycocalyx imparts a net negative luminal charge, impedance of CSA transport by mutual charge repulsion was also evaluated. Accordingly, CAM microvessels were pre-infused with protamine sulfate (100 μl/ml) to neutralize the negative charge. However, interstitial accumulation of FITC-CSA remained negligible. Thus, the presence of tight junctional clefts and paucity of plasmalemmal vesicles during CAM normigenesis probably serve as the principal morphologic correlates to the observed albumin restriction. Further, the normigenic CAM endothelium presents a more restrictive barrier to macromolecules than that of most angiogenic endothelia.
All Science Journal Classification (ASJC) codes
- Developmental Biology
- Cell Biology
- Chorioallantoic membrane
- Microvascular endothelium