Intracellular Digestion and Hydrolytic Enzymes in the Phagocytes of Planarians

Abstract

It has been established that, in those species studied, intraluminar digestion does not occur in triclad flatworms (Willier, Hyman and Rifenburgh, 1925;Jennings, 1957), but that digestion takes place within food vacuoles in the phagocytic cells of the gastrodermis. A number of investigators have observed the disintegration of ingested food particles within these cells (Arnold, 1909;Saint-Hilaire, 1910;Jacek, 1917;von Levitzow, 1943), but the methods they employed did not permit elucidation of the mechanisms involved except in a most general way. Kelley (1931), studying the intracelular digestion of nucleoprotein in D. dorotocephala by means of the Feulgen reaction with and without acid hydrolysis, showed that the ingested material was hydrolyzed within the first two hours.To our knowledge, no previous study has characterized the hydrolytic enzymes in the phagocytes of planarians. The present report considers the relationship of three such enzymes to current concepts of intracellular digestion. Materials and MethodsSpecimens of Dugesia dorotocephala and D. tigrina were used for this study. The animals were maintained as stock cultures at 18° C. and fed routinely once every ten days on minced rat or mouse liver. Experimental animals were isolated in fingerbowls and starved for at least three weeks. Some of these were fed raw rat or mouse liver, and others boiled liver to determine if enzyme activities in raw food were transferred to the gut. No differences in enzyme activities between animals fed raw or boiled liver were demonstrable by the staining methods employed. The worms were observed during feeding ; post-feeding times were determined from the moment the animals ceased feeding.For the demonstration of those enzyme activities surviving chemical fixation, specimens were initially fixed in warm (37° C.) Baker's calcium-formalin for 5 minutes to prevent discharge of the gut contents. They were then placed in calcium-formalin at 4° C. for 24 hours, washed for 5 minutes in distilled water and cut on a CCX-freezing microtome at 8-10/*. Material thus prepared was incubated for acid phosphatase activity by a slight modification of the method of Gomori (1952). Sections were incubated for 15-30 minutes in a 0.1 M 2glycerophosphate and lead nitrate mixture buffered to pH 5.0 with 0.05 M acetate buffer.Aminopeptidase activity was visualized by the method of Burstone and Folk (1956). Animals were placed on Monel grids and frozen in isopentane chilled by liquid nitrogen to -160° C. After quenching, the worms were dehydrated for 24 118, 315-323.

Acid and Alkaline Phosphatase Changes Associated With Feeding, Starvation and Regeneration in Planarians

“…This confirms the reports of Rosenbaum and Rolon (1960) and of Jennings (1962b). The enzyme reaction product at this time was in the form of small granules which gradually increased in size and numbers until they filled the entire cell by the second day after ingestion of food.…”

“…The apparently greater intensity and longer persistence of acid phosphatase activity in our preparations is probably due to better enzyme preservation in frozen sections than in paraffin-embedded material. There is general agreement that acid phosphatase and other acid hydrolases are involved in the initial stages of digestion in food vacuoles (Rosenbaum and Rolon, 1960;Miiller et al, 1962;Jennings, 1962b) but the function of the alkaline phosphatase which appears some hours after the beginning of digestion is unknown. Jennings (1962b) suggests that it "may be concerned in the release of energy needed for secretion of the various enzymes and the absorption of the products of digestion from the vacuoles."…”

Rotifer Symposium IV

“…Acid phosphatase is thought to playa role in the initial stages of digestion of exogenous and endogenous materials [Rosenbaum & Rolon, 1960;Tomlinson & Warren, 1960;Jennings, 1962;Osborne & Miller, 1963;Ryder & Bowen, 1975]. The physiological function of alkaline phosphatase is unknown [Reid & Wilson, 1971;Saleem & Alikhan, 1974].…”

Food ingestion by planarian intestinal phagocytic cells ? a study by scanning electron microscopy

“…Although events in the intracellular digestion have been well studied at the levels of the light microscope (Willier et al, 1925;Kelley, 193 1;Rosenbaum & Rolon, 1960;Jennings, 1957Jennings, , 1962Jennings, , 1974 and transmission electron microscope (Ishii, 1972;Pascolini & Gargiulo, 1975;Bowen et al, 1974;Bowen, 1980;Garcia-Corrales & Gamo, 1988), details of ingestion through phagocytosis remain obscure, largely because of technical limitations in observation of sections. A previous TEM study (Ishii, 1972) showed that during phagocytosis the surfaces of the phagocytic cells appeared labyrinthine and pseudopodia seemed to differ in shape according to the nature of the food ingested.…”