Binding of Escherichia coli heat-stable enterotoxin to receptors on rat intestinal cells

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Abstract
Whether receptors for E. coli heat-stable enterotoxin (ST) exist on intestinal epithelial cells was studied. Binding sites for 125I-ST were found on rat jejunal and ileal villus cells. Binding was rapid, reversible, linear with cell number, saturable and temperature dependent. Significant degradation of 125I-ST occurred when incubated with cells at 37.degree. C but not at 25.degree. C. Binding was specific to ST since binding of 125I-St was competitively inhibited by increasing concentrations of human or porcine ST but not by E. coli heat-labile, cholera or staphylococcal enterotoxins. Addition of excess unlabeled ST to cells preincubated with 125I-ST resulted in dissociation of much but not all of the bound 125I-ST. Binding of 125I-ST to jejunal and ileal cells occurs with 2 affinities; this is due to the phenomenon of negative cooperativity. The potency of ST for inhibiting the binding of 125I-ST was identical to the potency of ST in stimulating cGMP production. These data support the existence of receptors for ST on intestinal cells; these receptors may be involved in the action of ST.

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