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

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. 