Detection of distinct endocytotic and phagocytotic activities in epithelial cells (pinacocytes) of freshwater sponges (Porifera, Spongillidae) |
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Authors: | Beate Hahn-Keser W Stockem |
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Institution: | Institut für Zellbiologie, Universit?t Bonn, Ulrich-Haberland-Strasse 61 a, D-53121 Bonn, Germany Fax: 0228/735302, DE
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Abstract: | Light and electron microscopical investigations using externally applied fluorescent and gold-labeled markers have revealed
the existence of distinct endocytotic and phagocytotic activities in basal epithelial cells (pinacocytes) of the freshwater
sponges Spongilla lacustris and Ephydatia es) of the f. The total rate of endocytotic membrane uptake, ascertained by the
application of the cationic lipid probe TMA-DPH, was found to be 3.2% of the cell surface area/h. A typical fluid-phase endocytosis,
demonstrated by the use of the water-soluble membrane-impermeable tracers BCECF-dextran and LY-CH, participates in endocytotic
activity at a rate of 0.7% of the cell surface area/h and results in the formation of endosomes measuring 0.8–1 μm in diameter.
Moreover, the application of labeled BSA succeeded in the detection of a receptor-mediated endocytosis amounting to a concentration-dependent
uptake of 2.3–2.8% of the cell surface area/h. Coated pits and coated vesicles conveying the adsorbed BSA measure 0.3 μm in
diameter and are covered on the cytoplasmic face with a clathrin-like protein (HC, 180 kDa; LC, 30 kDa). To facilitate phagocytotic
activities, a series of fluorescent–labeled and chemically treated particles such as bacteria or latex beads have been successfully
employed. Accordingly, the measured values of phagocytic membrane uptake between 1 and 8% of the cell surface area/h depend
on the variety of size as well as the chemical nature of the different bioparticles and clearly point to phagocytosis as a
key mechanism for providing freshwater sponges with nourishment.
Accepted: 3 April 1997 |
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