AJP - Heart and Circulatory Physiology, Vol 242, Issue 5 890-H899, Copyright © 1982 by American Physiological Society
The bloodless rat: a new model for macromolecular transport studies across lung endothelium
E. E. Schneeberger and B. A. Neary
To examine the effect of circulating proteins on the passage of
intravenously injected native ferritin across pulmonary capillary
endothelium, rats were exchange transfused with FC-43 fluorocarbon emulsion
(FCE) under ether anesthesia. Protein concentration was reduced to less
than 1.1 mg/ml by exchange transfusion, followed by FCE containing 15, 30,
or 60 mg/ml of lyophilized rat serum protein (LRSP). Two minutes after
ferritin injection lungs were prepared for ultrastructural morphometry. The
diameter and numerical density of vesicles remained unchanged under all
experimental conditions; however, at 0.6 mg/ml of circulating protein there
was a 5- and 10-fold increase, respectively in percent vesicle (%VL) and
basement membrane labeling (BML) by ferritin. This was reversible; at 60
mg/ml of circulating protein %VL and BML was indistinguishable from
controls. Following a reduction of circulating protein to less than 1.1
mg/ml, the addition of 15 mg/ml LRSP reduced %VL but had no effect on BML.
This suggests that in addition to shuttling vesicles there may be a second
mechanism for the transport of ferritin, possibly involving
transendothelial chains of vesicles.
