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The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages
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 c...
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| Format: | Thesis |
| Language: | English |
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Division of Medical Biochemistry and Structural Biology
2018
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| _version_ | 1867613236693565440 |
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| access_status_str | Open Access |
| author | Begg, Michael John |
| author2 | Thilo, Lutz |
| author_browse | Begg, Michael John Thilo, Lutz |
| author_facet | Thilo, Lutz Begg, Michael John |
| author_sort | Begg, Michael John |
| collection | Thesis |
| description | 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. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/27137 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:56.154Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2018 |
| publishDateRange | 2018 |
| publishDateSort | 2018 |
| publisher | Division of Medical Biochemistry and Structural Biology |
| publisherStr | Division of Medical Biochemistry and Structural Biology |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/27137 The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages Begg, Michael John Thilo, Lutz Medical Biochemistry Endocytosis Macrophages - physiology Osmolar concentration 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. 2018-01-30T14:00:17Z 2018-01-30T14:00:17Z 1992 Master Thesis Masters MSc (Med) http://hdl.handle.net/11427/27137 eng application/pdf Division of Medical Biochemistry and Structural Biology Faculty of Health Sciences University of Cape Town |
| spellingShingle | Medical Biochemistry Endocytosis Macrophages - physiology Osmolar concentration Begg, Michael John The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages |
| thesis_degree_str | Master's |
| title | The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages |
| title_full | The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages |
| title_fullStr | The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages |
| title_full_unstemmed | The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages |
| title_short | The effect of hyperosmolarity on fluid-phase and receptor-mediated endocytosis in P388D1 macrophages |
| title_sort | effect of hyperosmolarity on fluid phase and receptor mediated endocytosis in p388d1 macrophages |
| topic | Medical Biochemistry Endocytosis Macrophages - physiology Osmolar concentration |
| url | http://hdl.handle.net/11427/27137 |
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