Interaction of cholera toxin and Escherichia coli enterotoxin with isolated intestinal epithelial cells.
The interaction of biologically active 125I-labeled cholera toxin with isolated chick intestinal epithelial cells involves a large number (approx 1.7 10(6)/cell) of high-affinity (Kd = 8-9 X 10(-9) M) binding sites that belong to a single class. Binding of iodotoxin to the cells occurs rapidly, is half-maximal within 1 min, and is complete in 3-7 min (at 37 degrees C) depending on the toxin concentration. Toxin binding is saturable and includes only a small contribution from nonspecific sites. Ligand competition studies suggest that the isolated B subunit of choleragen (CT-B) behaves in an almost identical fashion to the holotoxin (CT), whereas the A subunit shows no detectable activity in competitive binding. Assays for cAMP indicate that neither that A nor the B subunits of CT contain any activity for increasing the level of intracellular cAMP. B subunit, when incubated with CT, inhibits CT-induced elevation of cAMP in a dose-dependent manner. Preincubation of 125I-CT with various concentrations of ganglioside GM1 also shows a dose-dependent inhibitory effect on the binding activity of the toxin. Pretreatment of CT with increasing concentrations of GM1 results in a progressive decrease in toxin-induced formation of cAMP. Escherichia coli heat-labile enterotoxin, which is known to alter intestinal function via a mechanism similar to that of CT, has binding and biological effects very similar to those of CT.
D000818:Animals; D001665:Binding Sites; D002452:Cell Count; D002478:Cells, Cultured; D002645:Chickens; D002772:Cholera Toxin / Q000378:metabolism / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D004347:Drug Interactions; D004768:Enterotoxins / Q000378:metabolism / Q000494:pharmacology*; D004926:Escherichia coli; D005677:G(M1) Ganglioside / Q000494:pharmacology; D007421:Intestine, Small / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D014357:Trypsin / Q000494:pharmacology
D004768:Enterotoxins; D005677:G(M1) Ganglioside; D002772:Cholera Toxin; D000242:Cyclic AMP; D014357:Trypsin