THE PLASMA-MEMBRANE POLARITY OF HUMAN BILIARY EPITHELIAL-CELLS - IN-SITU IMMUNOHISTOCHEMICAL ANALYSIS AND FUNCTIONAL IMPLICATIONS

Background/Aims: In transporting epithelia, like the biliary epitheliu m, most plasma membrane proteins present a polarized distribution, ess ential for the maintenance of the structural and functional properties of the epithelium, We therefore analysed the expression of polarized plasma membrane proteins by human biliary epithelial cells in order to compare them with other transporting epithelial cells and to search f or differences in plasma membrane protein expression between their dif ferent anatomical subsets. Methods: We designed an in situ immunohisto chemical study of the various anatomical compartments of the human bil iary tract in order to assess the pattern of expression of selected po larized plasma membrane proteins, including integrin receptors, ectope ptidases, membrane transporters and GPI-linked proteins. Results: All biliary epithelial cells expressed the same repertoire of integrins, e xcept for integrin chain alpha 5, restricted to the intra-hepatic comp artments, All biliary epithelial cells expressed the following apical ectopeptidases: aminopeptidase-N, neutral-endopeptidase, dipeptidyl-pe ptidase IV. All biliary epithelial cells expressed the membrane transp orter Na+K+-ATPase, restricted to the basolateral domain, and the apic al transporters CFTR and MDR-1. The apical AE2 anion exchanger was res tricted to the small intra-hepatic bile ducts and the gallbladder, The GPI-linked protein protectin was basolateral in the: intrahepatic bil e ducts and apical in the gallbladder. Conclusions: The structural org anization of the plasma membrane of biliary epithelial cells is very s imilar to that of other simple epithelia and exhibits a limited degree of heterogeneity.