Influence of forskolin and carbachol on intestinal absorption of horseradish peroxidase in the goldfish (Carassius auratus) |
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Authors: | A J Kiliaan G Scholten P B Bijlsma K Dekker J A Groot |
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Institution: | (1) Institute for Neurobiology, University of Amsterdam, Kruislaan 320, 1098 SM Amsterdam, The Netherlands, NL |
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Abstract: | The transepithelial route for mucosa-to-serosa transport of the tracer macromolecule horseradish peroxidase (HRP; MW 40 kDa)
and modulation of this transport by forskolin and carbachol have been studied in vi-tro in stripped goldfish intestinal epithelium
mounted in Ussing-type chambers. Uptake and transport have been investigated by measuring the HRP flux from the muco-sal to
serosal sides by an enzymatic method and by visualising HRP reaction products in the mucosa with electron-microscopical techniques.
Both the cholinergic agonist carbachol (which is thought to increase intracellular Ca2+ and activate protein kinase C activity) and forskolin (a direct activator of adenylylcyclase) affect the amount of enzymatically
active HRP in the tissue. In control tissue, HRP product is found only within the epithelial cells, the transepithelial flux
reaching a constant value of about 1.5 pmoles/cm2 per h. Carbachol increases the amount of HRP product in the cells, but has no significant effect on the HRP flux compared
with control values. Forskolin decreases the amount of HRP product in the cells; however, in the presence of forskolin, the
lateral intercellular spaces become filled with HRP product. HRP is found in the lamina propria and the transepithelial protein
flux increases more than 2.5-fold. In the presence of forskolin plus carbachol, the results are no different from the control.
It is concluded that carbachol increases the endocytotic uptake of HRP, whereas forskolin inhibits the uptake but increases
the paracellular permeability for HRP in goldfish intestine.
Received: 10 July 1995 / Accepted: 4 February 1996 |
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Keywords: | : Intestine Endocytosis Tight junctions Carbachol Forskolin Transport Carassius auratus (Teleostei) |
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