What is it about?
Haematoporphyrin derivative (HpD) uptake, intracellular distribution and turnover were examined in a free-living protozoan cell, Paramecium aurelia, which had been demonstrated to internalize lipoproteins. A 10 min incubation in HpD completed with low-density lipoprotein (LDL) resulted in the appearance of distinct red-fluorescing vesicles, together with a diffuse fluorescence of the cytoplasm. Fluorescein labelling of LDL demonstrated the intracellular localization of HpD and LDL within the same vesicles. Pretreatment of Paramecium with the β-adrenergic antagonist l-propranolol, which blocked its phagocytotic activity, resulted in an absence of red-fluorescing vesicles; thus these were proved to be endosomes.
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Why is it important?
Fluorescence emission recorded in the endosomes was characterized by a band at about 660–670 nm which was attributed to the partially unfolded oligomers; this emission was present during maintenance of the cells in drug-free culture medium for up to 120 min. Propranolol-pretreated cells exhibited only a diffuse cytoplasmic fluorescence characterized by an emission band at 630 nm, which was attributed to the monomers; this disappeared rapidly on washing.
Perspectives
These results suggest the following: (i) HpD monomers enter Paramecium via transmembrane influx and/or fluid phase uptake; (ii) HpD oligomers are mainly internalized via receptor-mediated endocytosis; (iii) the extent of the endocytotic process is increased when HpD is completed with LDL; (iv) after internalization, aggregate species undergo a disaggregating process which accounts for the persistence of the intracellular fluorescence.
Professor Elzbieta Wyroba
Nencki Institute of Experimental Biology
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This page is a summary of: Uptake and distribution of haematoporphyrin derivative in the unicellular eukaryote Paramecium, Journal of Photochemistry and Photobiology B Biology, August 1990, Elsevier,
DOI: 10.1016/1011-1344(90)85114-c.
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