The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages

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dc.contributor.advisorThilo, Lutzen_ZA
dc.contributor.authorBegg, Michael Johnen_ZA
dc.date.accessioned2018-01-30T14:00:17Z
dc.date.available2018-01-30T14:00:17Z
dc.date.issued1992en_ZA
dc.description.abstractExtracellular components can be internalized by either receptor-mediated or fluid-phase endocytosis. Receptor-mediated endocytosis involves the internalization of receptor-ligand complexes into coated vesicles of about 0.1 μm in diameter. The average diameter of primary pinocytic vesicles has been calculated to be 0.24 - 0.28 μm. The discrepancy in size between coated vesicles and the average pinosome diameter can be explained if, in addition to coated vesicles, another endocytic process involving vesicles larger than 0.28 μm in diameter takes place. These two vesicle types could together produce an average diameter of 0.24 μm. This hypothesis suggests that coated vesicles cannot fully account for fluid-phase uptake. Hypertonic conditions can selectively inhibit receptor-mediated endocytosis, leaving fluid-phase uptake unaffected, again suggesting that an alternative to coated pit-mediated uptake exists. In this study we determined the volume-weighted average diameter of primary pinocytic vesicles under hypertonic conditions (0.52 osm) where receptor-mediated uptake of transferrin was selectively inhibited by 42%. Fluid-phase uptake of FITC-dextran was unaffected by 0.52 osm medium. The internalization rate of ³H-galactose-labelled plasma membrane was reduced from 2.6 %/min to 1.5 %/min. The decrease in the rate of membrane internalization, without a reduction in the rate of fluid uptake at hypertonicity, implied a reduced surface to volume ratio of the pinocytic vesicles formed under these conditions. This suggested an increase in the average diameter of primary pinocytic vesicles. Membrane internalization rates were calculated on the assumption that all labelled cell-surface constituents were internalized to the same relative extent, as has been shown previously for isotonic conditions. This assumption was also shown to hold true under isotonic conditions. The reduced rate of membrane internalization under hypertonic conditions was shown not to be due to the exclusion of any labelled protein species from internalized vesicles. The larger average vesicle size determined under conditions of selective reduction of coated vesicle formation (i.e. hypertonicity), demonstrates the existence of a population of larger pinosomes involved in a possible alternative mechanism to coated-pit-mediated endocytosis.en_ZA
dc.identifier.apacitationBegg, M. J. (1992). <i>The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages</i>. (Thesis). University of Cape Town ,Faculty of Health Sciences ,Division of Medical Biochemistry & Structural Biology. Retrieved from http://hdl.handle.net/11427/27137en_ZA
dc.identifier.chicagocitationBegg, Michael John. <i>"The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages."</i> Thesis., University of Cape Town ,Faculty of Health Sciences ,Division of Medical Biochemistry & Structural Biology, 1992. http://hdl.handle.net/11427/27137en_ZA
dc.identifier.citationBegg, M. 1992. The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Begg, Michael John AB - Extracellular components can be internalized by either receptor-mediated or fluid-phase endocytosis. Receptor-mediated endocytosis involves the internalization of receptor-ligand complexes into coated vesicles of about 0.1 μm in diameter. The average diameter of primary pinocytic vesicles has been calculated to be 0.24 - 0.28 μm. The discrepancy in size between coated vesicles and the average pinosome diameter can be explained if, in addition to coated vesicles, another endocytic process involving vesicles larger than 0.28 μm in diameter takes place. These two vesicle types could together produce an average diameter of 0.24 μm. This hypothesis suggests that coated vesicles cannot fully account for fluid-phase uptake. Hypertonic conditions can selectively inhibit receptor-mediated endocytosis, leaving fluid-phase uptake unaffected, again suggesting that an alternative to coated pit-mediated uptake exists. In this study we determined the volume-weighted average diameter of primary pinocytic vesicles under hypertonic conditions (0.52 osm) where receptor-mediated uptake of transferrin was selectively inhibited by 42%. Fluid-phase uptake of FITC-dextran was unaffected by 0.52 osm medium. The internalization rate of ³H-galactose-labelled plasma membrane was reduced from 2.6 %/min to 1.5 %/min. The decrease in the rate of membrane internalization, without a reduction in the rate of fluid uptake at hypertonicity, implied a reduced surface to volume ratio of the pinocytic vesicles formed under these conditions. This suggested an increase in the average diameter of primary pinocytic vesicles. Membrane internalization rates were calculated on the assumption that all labelled cell-surface constituents were internalized to the same relative extent, as has been shown previously for isotonic conditions. This assumption was also shown to hold true under isotonic conditions. The reduced rate of membrane internalization under hypertonic conditions was shown not to be due to the exclusion of any labelled protein species from internalized vesicles. The larger average vesicle size determined under conditions of selective reduction of coated vesicle formation (i.e. hypertonicity), demonstrates the existence of a population of larger pinosomes involved in a possible alternative mechanism to coated-pit-mediated endocytosis. DA - 1992 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1992 T1 - The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages TI - The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages UR - http://hdl.handle.net/11427/27137 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/27137
dc.identifier.vancouvercitationBegg MJ. The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages. [Thesis]. University of Cape Town ,Faculty of Health Sciences ,Division of Medical Biochemistry & Structural Biology, 1992 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/27137en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDivision of Medical Biochemistry and Structural Biology
dc.publisher.facultyFaculty of Health Sciencesen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherMedical Biochemistryen_ZA
dc.subject.otherEndocytosisen_ZA
dc.subject.otherMacrophages - physiologyen_ZA
dc.subject.otherOsmolar concentrationen_ZA
dc.titleThe effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophagesen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMSc (Med)en_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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