Ultrastructural and cytochemical aspects of the basophilic cells in the hepatopancreas of Aplysia depilans (Mollusca, Opisthobranchia)

The basophilic cells of Aplysia depilans have a pyramidal shape and a large nucleus usually located near the center or in the basal half of the cell. The nucleus possesses several clumps of condensed chromatin and a prominent nucleolus. The great profusion of rough endoplasmic reticulum cisterns in a major feature of these cells. Secretion granules are accumulated in the a pical zone, and arylsulphatase was detected in some of them. In some basoph ilic cells a very substantial part of the cell volume was occupied by clear vacuoles, some of them reaching 9 mu m However, in other cells only a few vacuoles were observed. Probably the cells with just a few vacuoles are sti ll young, and after a progressive accumulation, the vacuoles become abundan t in old cells. The presence of a dark nucleus in the cells with a large nu mber of vacuoles suggests that they are in a final stage of their life. Ary lsulphatase was detected in the vacuoles and also in small secondary lysoso mes containing substances in digestion. Bundles of tubules with 50 nm in di ameter were found within some cisterns of rough endoplasmic reticulum, A ce ll fraction enriched in mannitol oxidase, extracted from the hepatopancreas of a terrestrial slug, consisted in very similar tubular structures. Using a histochemical method, mannitol oxidase was detected in the basophilic ce lls of A. depilans, and it may be associated with the tubular structures of the endoplasmic reticulum, This is the first report of mannitol oxidase in opisthobranch molluscs, Almost spherical peroxisomes with a small nucleoid were abundant in these cells. The nucleoids presented a rectangular sectio n, but a crystalline structure was not evident. The peroxisomes were staine d after the cytochemical detection of catalase activity.