An electron microscopic and histochemical study of the secretory cells inHydra viridis.

The fresh water coelenterateHydra viridis possesses a unique distribution of mucous and serous secretory cells in the gastrodermis. The mucous cells are found only in the hypostome, a region devoid of the serous zymogen cells. On the other hand, the zymogen cells are found extending from the tentacles to the peduncle. Histochemical stains indicated that the two hypostomal mucous cells, spumous and granular, secreted an acid mucopolysaccharide, and incorporated radiosulfate. The radiosulfate label was not sensitive to hyaluronidase digestion, but was removed by acid methanolysis. In contrast, the secretory product of the zymogen cell was rich in proteins and a PAS-positive moiety (unsulfated).The ultrastructure of these cells was correlated with their histochemical staining properties. It was demonstrated that glutaraldehyde preserved the ultrastructure of the secretory granules better than osmium, and also preserved more components within the granules. The mucous cell granules contained an electrolucent and an electron dense component. The cells were both PAS-positive and alcianophilic. After osmium fixation the dense component was lost and the cells were primarily alcianophilic. Osmium also failed to preserve the electron dense component in the zymogen cells.Observations of corresponding thick and thin sections showed a cell containing granules similar to the granules seen in mouse Paneth cells. The dense core was osmiophilic and the lighter halo was alcianophilic.These results lead us to conclude that the electrolucent filamentous component is an alcianophilic acid mucopolysaccharide and the dense granular component is probably a PAS-positive material.