Pb. Bijlsma et al., CARBACHOL, BUT NOT FORSKOLIN, INCREASES MUCOSAL-TO-SEROSAL TRANSPORT OF INTACT PROTEIN IN RAT ILEUM IN-VITRO, American journal of physiology: Gastrointestinal and liver physiology, 34(1), 1996, pp. 147-155
The effects of the secretagogues forskolin and carbachol on protein up
take in isolated ileum of rats were studied. The mucosal-to-serosal tr
ansport of horseradish peroxidase (HRP, mol mass 40 kDa) was measured
in Ussing chambers, and afterwards tissues were processed for electron
microscopy. In the absence of secretagogues, the flux of enzymaticall
y active HRP was 5 pmol . cm(-2) . h(-1) at a mucosal concentration of
10 mu M Electron micrographs showed vesicles filled with active HRP i
n enterocytes but no HRP activity in intercellular spaces. Forskolin d
ecreased HRP activity in the cells. Carbachol increased the amount of
HRP-filled vesicles in enterocytes and induced HRP filling in some int
ercellular spaces and tight junctions in the upper parts of the villi.
The transepithelial flux of intact HRP increased more than 2.5-fold.
This effect was suppressed by atropine. We conclude that cholinergic a
ctivation can increase the uptake of intact protein via endocytosis an
d the transepithelial passage by the induction of a diffusional parace
llular pathway. We speculate that the increased transport of intact pr
otein through the intestinal barrier may influence immunologic sensiti
zation to food allergens.