Miscellaneum : Exocytosis in "Entamoeba"

Exocytosis in Entamoeba is described in which the vacuole moves posteriorly and comes out of the tail or the uroid. Sometimes the whole vacuole comes out but more often only a part of it is expelled. The remaining part gets detached and moves back into the cytoplasm. Introduction A considerable amout of information is available on the method of food ingestion by Entamoeba (Zaman, 1970; Wkstphal & Michel. 1971) but little is known about the method of excretion by this cell. The fate of ingested food particles in Entamoeba is very intriguing as the parasite is capable of ingesting a variety of particulate matter including latex particles, various dyes and its own cysts (McConnachie. 1955). The amoeba must, therefore, possess an effective mechanism of excretion or exocytosis for those substances which it is unable to digest. In a previous study it was suggested that the tail or uroid of Entamoeba probably has an excretory function (Zaman, 1961). In that study the actual mode of excretion, however, was not recorded. In this paper photographic evidence is presented to show how this process takes place. Material and Methods Entamoeba invadens was used for this study as this species is active at room temperature and spreads out well on microscope slides. Light microscopy was done in Reichert '"Zetopan" microscope using a negative (anoptral), and Leitz "Ortholux" microscope using a positive phase contrast. Photographs were taken in both instances with an electronic flash at time intervals of approximately 4 seconds. Preparations for electron microscopy were made by washing 7-day old cul¬ tures of Entamoeba in physiological saline and fixing the heavy suspension of trophozoites in ice cold 4"/o glutaraldehyde in phosphate buffer (pH 7.4. Millonig. 1962). The glutaraldehyde fixed cells were washed once in Millonig phosphate buffer without additives and then post fixed for one hour in ice-cold 1 °'o Osmium tetroxide, also in the same phosphate buffer. Specimens were dehydrated in ethanol series and with two additional 15 minute changes in propylene oxide. Embedding was done in "Araldite" according to standard technique. Sections were cut with a Porter Blum microtome and examined after staining with uranyl acetate and lead citrate (Reynolds. 1963) at 50 kv in a Hitachi HS8 electron microscope. Results Observations in the light microscope showed that during excretion one of the vacuoles moved posteriorly and came into the tail region. Subsequently the whole of it came out of the tail. The tail during this process showed an elongated cleft through which the expulsion occurred. When only part of the vacuole was 170 Ada Tropica XXX, 1-2, 1973 Miscellaneum M fSm ••¦« •y -i ^ ^ fm S?"> 4» •-. ^Äfc. %,> •./ <w * ^« % Ü X jb*+*& •**% --<