Mucin histochemistry of the digestive tract of the red-legged frog Rana aurora aurora

Mucous cells from the digestive tract of the red-legged frog, Rana aurora a urora, were examined by standard histochemical methods and by lectin histoc hemistry. Two different goblet cell types were found in the oesophageal epi thelium. Type I cells produced acidic glycoproteins with beta1,4GlcNAc olig omers, Gal beta1,3GalNAc sequences, sulphated esters on internal residues a nd abundant non-O-acylated terminal sialic acid bound to penultimate GalNAc . These cells also reacted with Con-A after periodate oxidation-borohydride reduction (PCS). Type II goblet cells mainly differed from type I cells in their negative reaction with PCS. Oesophageal glands consisted of mucous a nd serous cells. Mucous cells produced neutral stable class III mucosubstan ces with GalNAc, beta1,4GlcNAc and Gal beta1,3GalNAc residues. Gastric surf ace cells produced sulpho-sialoglycoproteins with Gal beta1,3GalNAc residue s and Gal beta1,3GalNAc-sialic acid as terminal sequences. These cells did not contain stable class III mucosubstances. The mucus produced by foveolar cells was similar in composition but did not contain sulphated groups and was rich in GalNAc residues. The fundic glands consisted of mucous neck cel ls, endocrine cells and oxyntic cells. The neck cells produced neutral muci ns containing D-mannose and/or D-glucose, beta1,4GlcNAc oligomers and Gal b eta1,3GalNAc terminal dimers and were PCS-positive. Pyloric glands were of the mucus-secreting type, which produced glycoproteins with the same basic features as those produced in fundic neck cells. A single type of intestina l goblet cells produced acidic glycoproteins rich in beta1,4GlcNAc oligomer s, sulphated esters on oligosaccharide chains and terminal O-acylated siali c acid bound to penultimate Gal beta1,3GalNAc. The different carbohydrate s tructures observed along the digestive tract of the frog may reflect specif ic functions of the mucus.