Interaction of epidermal growth factor with specific binding sites of enterocytes isolated from rat small intestine...

Isolated enterocytes from rat small intestine were characterized for their specific binding of epidermal growth factor (EGF). Intestinal epithelial cells were isolated at 4 degrees C to minimize the loss of receptor sites during the isolation procedure. 125I-labelled EGF binding to enterocytes from adult rats was found to be specific, saturable, temperature dependent and trypsin sensitive. Binding performed in the presence of a lysosomotropic agent (NH4Cl) increased the time required to reach maximal binding at 25 degrees C. NH4Cl had no significant effect on the time-course of EGF binding at 4 degrees C and 37 degrees C. A Scatchard plot showed a curvilinear relationship indicating that EGF binds to enterocytes with more than one binding site. Developmentally, enterocytes from fetuses and pups showed characteristic temperature dependence and trypsin sensitivity, but with different levels of binding to EGF. Specific EGF binding was demonstrably higher in enterocytes from small intestine of term fetuses. EGF binding to isolated enterocytes declined rapidly after birth, and the level stayed fairly constant thereafter. Pretreatment of enterocytes from fetal intestine with mature rat milk led to a dose-dependent decrease in EGF binding. These results suggest the presence of endogenous milk factors that modify EGF binding and account for, at least partly, the observed rapid decrease of EGF binding after birth.