Effect of luminal epidermal growth factor on enterocyte glucose and proline transport

The effect of luminal epidermal growth factor (EGF; 60 ng/ml) and tyrphostin-51 (TYR; 10 microM), a tyrosine kinase inhibitor, on rabbit jejunal brush-border and basolateral membrane transport was investigated. In separate experiments, the effect of EGF, EGF and TYR, or TYR alone was examined in in vivo loops. In addition, Na+ permeability in brush-border membrane vesicles (BBMV) and the effect of Ca2+ channel blockade on EGF-stimulated glucose uptake were examined. Luminal EGF significantly (P < 0.0001) increased the maximal rate of transport (Vmax) for glucose and proline uptake in BBMV. TYR and Ca2+ channel blockade completely abolished the EGF-induced increase in glucose transport and in the case of TYR resulted in a significant reduction in Vmax compared with controls (P < 0.0001). The Michaelis-Menten constant did not differ in any experimental group. EGF had no effect on brush-border Na+ permeability or basolateral membrane glucose transport. The findings indicate a role for EGF in the acute regulation of jejunal brush-border membrane nutrient uptake. Furthermore, tyrosine kinase activity appears to be involved both in mediating EGF-induced alterations in transport function and in the maintenance of basal brush-border membrane function.