Ultrastructure of the pyloric endocrine cells in the cartilaginous fish Scyliorhinus stellaris

Abstract

In the pyloric mucosa of Scyliorhinus stellaris at least eight cell types can be identified, showing well-differentiated ultrastructural features, especially in the secretory granules. With semithin/ultrathin techniques only some of these cells are easily demonstrable. Type I and Type II cells can be considered as enterochromaffin (EC) cells since both are positive to argentaffin reaction, but the ultrastructural features of the granules are quite dissimilar. Type III cells could not be found in the semithin sections but the aspect of the granules is like that in the intestinal EC cells. Type IV cells contain round vesicular granules with an eccentric, highly osmiophilic core in which the number and size of the granules can vary from cell to cell. This cell type is positive to the Grimelius silver reaction and may be equivalent to the gastrin storing or gastrin-cholecystokinin storing cell. Type V cells contain round granules with a clear halo showing a weakly positive Grimelius silver reaction. Histochemically this cell type resembles the pancreatic A cell but the granule size is slightly different. Type VI cells are characterized by argyrophilic and non-argentaffin granules, round or rod-shaped. Type VII and Type VIII cells show similarities with two pancreatic cell types. The Type VII may be a D cell. All pyloric endocrine cells except cell Type III are of Fujita's “open” type.