Transport of insulin and albumin by the microvascular endothelium of the rete mirabile

M Bendayan, EA Rasio - Journal of Cell Science, 1996 - journals.biologists.com
M Bendayan, EA Rasio
Journal of Cell Science, 1996journals.biologists.com
Vascular permeability for albumin and insulin in the continuous capillary network of the rete
mirabile of the eel swimbladder was evaluated by ultrastructural immunocytochemistry and
countercurrent perfusion experiments. Upon perfusion of the rete capillaries with a buffer
solution containing albumin and insulin, these serum proteins were revealed at the electron
microscope level, by the Protein A-gold immunocytochemical technique on a post-
embedding step. For the simultaneous detection of both proteins, the double labeling …
Abstract
Vascular permeability for albumin and insulin in the continuous capillary network of the rete mirabile of the eel swimbladder was evaluated by ultrastructural immunocytochemistry and countercurrent perfusion experiments. Upon perfusion of the rete capillaries with a buffer solution containing albumin and insulin, these serum proteins were revealed at the electron microscope level, by the Protein A-gold immunocytochemical technique on a post-embedding step. For the simultaneous detection of both proteins, the double labeling technique with different sized gold particles was used. Furthermore, labeling was performed with the mixture of anti-albumin and anti-insulin antibodies. The labelings obtained were morphometrically evaluated and demonstrate that: (1) serum proteins such as albumin and insulin are transported by the endothelial cells through their plasmalemmal vesicular system; (2) insulin is transported preferentially to albumin; and (3) this transport involves different populations of plasmalem-mal vesicles. Measurements of diffusion permeability coefficients have confirmed the preferential transport of insulin, its coefficient being higher than that of albumin. Conversely, when compared to that of inulin or sucrose, which are assumed to be markers of the paracellular diffusion, it was found to be much lower, indicating that transcytosis through the vesicular system is less efficient than diffusion along the intercellular junctions. These results indicate that transcytosis of insulin and albumin occurs via different sets of plasmalemmal vesicles, probably through receptor-mediated mechanisms, and that the overall rate of transport across the rete capillaries, with respect to paracellular diffusion, is higher for insulin than for albumin.
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