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1 CURE: Digestive Diseases Research Center, West Los Angeles Veterans Affairs Medical Center, School of Medicine, University of California, Los Angeles 70073; and 2 Department of Surgery and Physiology, School of Medicine, University of California, San Francisco, California 94143
Previous studies found that
monolayers formed from canine oxyntic epithelial cells in primary
culture displayed remarkable resistance to apical acidification and
both mitogenic and migratory responses to epidermal growth factor (EGF)
treatment. In our present studies, we found that EGF increased
transepithelial resistance (TER) but not short-circuit current in these
monolayers. Parallel effects of EGF on decreasing mannitol flux and
increasing TER implicate direct regulation of paracellular
permeability. EGF acting at either apical and basolateral receptors
rapidly increased TER, but the apical response was sustained whereas
the basolateral response was transient. 125I-labeled EGF
binding revealed specific apical binding, but receptor numbers were
25-fold lower than on the basolateral surface. Both apical and
basolateral EGF activated tyrosine phosphorylation of EGF receptors
(EGFR),
-catenin, and cellular substrate as evident on confocal
microscopy. Although apical EGF activated a lesser degree of receptor
autophosphorylation than basolateral EGF, phosphorylation of
-catenin was equally prominent with apical and basolateral receptor
activation. Together, these findings indicate that functional apical
and basolateral EGFR exist on primary canine gastric epithelial cells
and that these receptors regulate paracellular permeability. The
sustained effect of apical EGFR activation and prominent
phosphorylation of
-catenin suggest that apical EGFR may play a key
role in this regulation.
epidermal growth factor receptors; transforming growth factor receptors; gastric mucosal defense; paracellular pathway
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