Histochemical and immunohistochemical characterization of exocrine cells in the foregut of the red-eared slider turtle, Trachemys scripta (Emydidae).

The morphofunctional organization of the exocrine cells in the foregut of the red-eared slider turtle, Trachemys scripta, was investigated by histochemistry (PAS, AB pH1.0 and pH 2.5, HID-AB, Bowie), lectin-histochemistry (WGA, SBA, UEA, ConA, PNA, DBA, sialidase-SBA, sialidase-PNA, Paradoxical ConA), and immunohistochemistry (antipepsin, anti-alpha-H+,K+ ATPase) to detect regional differences and verify the existence of an oro-aboral gradient in gastric juice secretion. Observations showed that pharyngeal goblet cells have mucins with terminal residuals of GalNAc and sialic acid. In the oesophagus, sulphomucins in the goblet cells are progressively substituted by sialomucins and no glands are found. Gastric surface cells secrete mostly sialomucins with residuals of GlcNAc and GalNAc. The cardias presents glands with cells secreting mostly sialomucins, differing from the surface ones in having GalNAcalpha1,3GalNAc sequences. The fundus presents complex glands with main and lesser tubules. Cells in the main tubules secrete stable, class-III mucins with sialylated residuals of glucose and/or mannose, GalNAcalpha1, 3GalNAc, and Galbeta1,3GalNAc sequences. In the lesser tubules, the oxynticopeptic cells are found, presenting pepsinogen granules and an affinity to the anti-alpha-H+,K+ ATPase, without any oro-aboral variation. The pyloric glands have a secretion similar to that of the neck cells of the fundic glands, consisting of stable, class-III mucins mostly sialylated with a high heterogeneity of residuals such as glucose and/or mannose, fucose, GlcNAc, and GalNAc. Mucins in the foregut are probably involved in several functions such as lubrication, protection against gastric juice, osmotic regulation to increase intestinal absorption, and protection against microbial injuries.