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

Summary Mucous cells from the digestive tract of the red-legged frog, Rana aurora aurora , were examined by standard histochemical methods and by lectin histochemistry. Two different goblet cell types were found in the oesophageal epithelium. Type I cells produced acidic glycoproteins with β 1,4GlcNAc oligomers, Gal β 1,3GalNAc sequences, sulphated esters on internal residues and 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 and serous cells. Mucous cells produced neutral stable class III mucosubstances with GalNAc, β 1,4GlcNAc and Gal β 1,3GalNAc residues. Gastric surface cells produced sulpho-sialoglycoproteins with Gal β 1,3GalNAc residues and Gal β 1,3GalNAc-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 cells, endocrine cells and oxyntic cells. The neck cells produced neutral mucins containing D-mannose and/or D-glucose, β 1,4GlcNAc oligomers and Gal β 1,3GalNAc 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 intestinal goblet cells produced acidic glycoproteins rich in β 1,4GlcNAc oligomers, sulphated esters on oligosaccharide chains and terminal O-acylated sialic acid bound to penultimate Gal β 1,3GalNAc. The different carbohydrate structures observed along the digestive tract of the frog may reflect specific functions of the mucus.