INTESTINAL CELL MEMBRANES: STRUCTURE AND FUNCTION

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The long-term objective is to define the role of enterocyte plasmelemmal glyco-proteins in the control of its differentiation into a functional absorptive cell. Work over the last 25-years have indicated that the oligosaccharides of plasmalemmal glycoproteins influence cell differentiation as cell-cell recognition and as cell adhesion factors. The latter are important in determining tissue organization during differentiation particularly where the separation of the plasmalemma into domains may determine vector-directed cell function as in absorption. Our specific aims are; 1) to determine the structural changes in enterocyte plasmalemmal oligosaccharides associated with enterocyte differentiation and cell polarity, and 2) to relate these changes to enterocyte-to-intestinal basement membrane (IBM) adhesion, and interrelationship critical to tissue organization and normal intestinal absorption. Rat enterocytes will be isolated in fractions representative of the crypt-to-villus gradient of differentiation. The different domains (i.e., microvillus, lateral, and basal) of the enterocyte plasmalemma will be separated as well as the different parts of the Golgi. Nucleotide-sugar translocation and newly defined enzymes specific for different Golgi subunits will be used. A basal-enriched membrane will be detected by antibodies to glycoproteins immunocytologically associated with the basal plasmalemma. The possibility that IBM components retain association with basal membrane or that the basal domain has specific IBM receptors will be tested. Oligosaccharides isolated from these plasmalemmal domains will be analyzed by controlled hydrolysis, substrate and lectin affinity chromatography and by GLC and HPLC separation. Initially the goal will be to determine the oligosaccharide structures most characteristic of a particular plasmalemmal domain. The relationship of these oligosaccharides to cell-IBM adhesion will be studied using assays for cell adhesion; matrices derived from IBM will be used to test adhesion of tissue culture cells and of isolated enterocytes. these studies should provide information on how enterocyte polarity is developed and maintained during differentiation. Incomplete differentiation and decreased enterocyte polarity are general expressions of enterocyte injury and malfunction seen in many intestinal diseases. Our research should contribute to an understanding of the fundamental cell biology controls in tissue organization so important to intestinal absorption and secretion.