Aj. Kiliaan et al., INFLUENCE OF FORSKOLIN AND CARBACHOL ON INTESTINAL-ABSORPTION OF HORSERADISH-PEROXIDASE IN THE GOLDFISH (CARASSIUS-AURATUS), Cell and tissue research, 285(1), 1996, pp. 51-56
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 vitr
o in stripped goldfish intestinal epithelium mounted in Ussing-type ch
ambers. Uptake and transport have been investigated by measuring the H
RP flux from the mucosal to serosal sides by an enzymatic method and b
y visualising HRP reaction products in the mucosa with electron-micros
copical techniques. Both the cholinergic agonist carbachol (which is t
hought to increase intracellular Ca2+ and activate protein kinase C ac
tivity) and forskolin (a direct activator of adenylylcyclase) affect t
he amount of enzymatically active HRP in the tissue. In control tissue
, HRP product is found only within the epithelial cells, the transepit
helial flux reaching a constant value of about 1.5 pmoles/cm(2) per h.
Carbachol increases the amount of HRP product in the cells, but has n
o significant effect on the HRP flux compared with control values. For
skolin decreases the amount of HRP product in the cells; however, in t
he presence of forskolin, the lateral intercellular spaces become fill
ed with HRP product. HRP is found in the lamina propria and the transe
pithelial protein flux increases more than 2.5-fold. In the presence o
f forskolin plus carbachol, the results are no different from the cont
rol. It is concluded that carbachol increases the endocytotic uptake o
f HRP, whereas forskolin inhibits the uptake but increases the paracel
lular permeability for HRP in goldfish intestine.