Glutamine and barrier function in cultured Caco-2 epithelial cell monolayers

Dietary glutamine (Gin) has been shown to be important for maintenance of the intestinal barrier. To investigate the role of the epithelium in this Gin dependence, Caco-2 cells were raised on semipermeable membranes under conditions that model different regions of the crypt and villus. Gin availability was controlled by addition to the medium and treatment with methionine sulfoximine to inhibit Gin synthetase (GS). Barrier function was assayed by measuring transepithelial electrical resistance and fluxes of [C-14]mannitol and fluoroscein isothiocyanate-dextran. The barrier function of these monolayers was found to require the Gin provided either in the medium at the apical or basal surface or via GS. However, the barrier was no more sensitive to Gin deprivation than it was to accumulation or maintenance of total protein. These results suggest that the in vivo dependence of the gut mucosal barrier on Gin likely involves roles separate from maintenance of the epithelial barrier per se.