Glycoprotein synthesis, transport, and secretion by epithelial cells of human rectal mucosa: normal and cystic fibrosis

Abstract

The synthesis, transport, and secretion of glycoprotein by human rectal epithelium from normal volunteers, patients with cystic fibrosis, and their disease-free siblings were studied by autoradiography of rectal biopsies pulse-labeled with 3H-glucosamine and maintained in organ culture for various intervals of up to 24 hours. Human rectal goblet and columnar cells transported 3H-glucosamine-labeled secretory products at a substantially slower rate than do comparable colonic cells in smaller mammals. Within any one biopsy sample, the movement of labeled mucus in goblet cells varied widely among cells. Even with individual cells, labeled mucous granules often did not move in concert toward the apical cell surface. Average transport time in the cells of six cystic fibrosis patients and six sibling controls did not differ significantly from those of four adult controls. The carbohydrate composition of glycoprotein secretions of rectal epithelial cells was investigated by comparing autoradiographs of 3H-glucosamine-labeled biopsies with those labeled with 3H-fucose, 3H-N-acetylmannosamine, and 35S-sulfate. The patterns of incorporation of these four precrusors into normal goblet and columnar cells suggested that both cell types may alter the quantity and composition of newly synthesized glycoproteins as they migrate, mature, and senesce. Incorporation patterns in cystic fibrosis biopsies were indistinguishable from those of sibling or adult controls. With the techniques used, no abnormalities of epithelial glycoprotein production were detected in cystic fibrosis rectal mucosa.