Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q]
Herein we demonstrate how nanojunctions between lysosomes and sarcoplasmic reticulum (L-SR junctions) serve to couple lysosomal activation to regenerative, ryanodine receptor-mediated cellular Ca2+ waves. In pulmonary artery smooth muscle cells (PASMCs) it has been proposed that nicotinic acid adeni...
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| Format: | Article |
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F1000 Research Ltd
2014-04-01
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| Online Access: | http://f1000research.com/articles/3-93/v1 |
| _version_ | 1818361069355139072 |
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| author | Nicola Fameli Oluseye A. Ogunbayo Cornelis van Breemen A. Mark Evans |
| author_facet | Nicola Fameli Oluseye A. Ogunbayo Cornelis van Breemen A. Mark Evans |
| author_sort | Nicola Fameli |
| collection | DOAJ |
| description | Herein we demonstrate how nanojunctions between lysosomes and sarcoplasmic reticulum (L-SR junctions) serve to couple lysosomal activation to regenerative, ryanodine receptor-mediated cellular Ca2+ waves. In pulmonary artery smooth muscle cells (PASMCs) it has been proposed that nicotinic acid adenine dinucleotide phosphate (NAADP) triggers increases in cytoplasmic Ca2+ via L-SR junctions, in a manner that requires initial Ca2+ release from lysosomes and subsequent Ca2+-induced Ca2+ release (CICR) via ryanodine receptor (RyR) subtype 3 on the SR membrane proximal to lysosomes. L-SR junction membrane separation has been estimated to be < 400 nm and thus beyond the resolution of light microscopy, which has restricted detailed investigations of the junctional coupling process. The present study utilizes standard and tomographic transmission electron microscopy to provide a thorough ultrastructural characterization of the L-SR junctions in PASMCs. We show that L-SR nanojunctions are prominent features within these cells and estimate that the junctional membrane separation and extension are about 15 nm and 300 nm, respectively. Furthermore, we develop a quantitative model of the L-SR junction using these measurements, prior kinetic and specific Ca2+ signal information as input data. Simulations of NAADP-dependent junctional Ca2+ transients demonstrate that the magnitude of these signals can breach the threshold for CICR via RyR3. By correlation analysis of live cell Ca2+ signals and simulated Ca2+ transients within L-SR junctions, we estimate that “trigger zones” comprising 60–100 junctions are required to confer a signal of similar magnitude. This is compatible with the 110 lysosomes/cell estimated from our ultrastructural observations. Most importantly, our model shows that increasing the L-SR junctional width above 50 nm lowers the magnitude of junctional [Ca2+] such that there is a failure to breach the threshold for CICR via RyR3. L-SR junctions are therefore a pre-requisite for efficient Ca2+signal coupling and may contribute to cellular function in health and disease. |
| first_indexed | 2024-12-13T21:10:49Z |
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| issn | 2046-1402 |
| language | English |
| last_indexed | 2024-12-13T21:10:49Z |
| publishDate | 2014-04-01 |
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| spelling | doaj.art-6dd58fcd87ce4cc8bcc4dfbe989da8ef2022-12-21T23:31:21ZengF1000 Research LtdF1000Research2046-14022014-04-01310.12688/f1000research.3720.13986Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q]Nicola Fameli0Oluseye A. Ogunbayo1Cornelis van Breemen2A. Mark Evans3Current address: Institute for Biophysics, Medical University of Graz, Graz, 8010, AustriaCentre for Integrative Physiology, University of Edinburgh, Edinburgh, EH8 9XD, UKDepartment of Anesthesiology, Pharmacology, and Therapeutics, University of British Columbia, Vancouver, V6T 1Z3, CanadaCentre for Integrative Physiology, University of Edinburgh, Edinburgh, EH8 9XD, UKHerein we demonstrate how nanojunctions between lysosomes and sarcoplasmic reticulum (L-SR junctions) serve to couple lysosomal activation to regenerative, ryanodine receptor-mediated cellular Ca2+ waves. In pulmonary artery smooth muscle cells (PASMCs) it has been proposed that nicotinic acid adenine dinucleotide phosphate (NAADP) triggers increases in cytoplasmic Ca2+ via L-SR junctions, in a manner that requires initial Ca2+ release from lysosomes and subsequent Ca2+-induced Ca2+ release (CICR) via ryanodine receptor (RyR) subtype 3 on the SR membrane proximal to lysosomes. L-SR junction membrane separation has been estimated to be < 400 nm and thus beyond the resolution of light microscopy, which has restricted detailed investigations of the junctional coupling process. The present study utilizes standard and tomographic transmission electron microscopy to provide a thorough ultrastructural characterization of the L-SR junctions in PASMCs. We show that L-SR nanojunctions are prominent features within these cells and estimate that the junctional membrane separation and extension are about 15 nm and 300 nm, respectively. Furthermore, we develop a quantitative model of the L-SR junction using these measurements, prior kinetic and specific Ca2+ signal information as input data. Simulations of NAADP-dependent junctional Ca2+ transients demonstrate that the magnitude of these signals can breach the threshold for CICR via RyR3. By correlation analysis of live cell Ca2+ signals and simulated Ca2+ transients within L-SR junctions, we estimate that “trigger zones” comprising 60–100 junctions are required to confer a signal of similar magnitude. This is compatible with the 110 lysosomes/cell estimated from our ultrastructural observations. Most importantly, our model shows that increasing the L-SR junctional width above 50 nm lowers the magnitude of junctional [Ca2+] such that there is a failure to breach the threshold for CICR via RyR3. L-SR junctions are therefore a pre-requisite for efficient Ca2+signal coupling and may contribute to cellular function in health and disease.http://f1000research.com/articles/3-93/v1Cell SignalingCell Signaling & Trafficking StructuresMacromolecular Assemblies & Machines |
| spellingShingle | Nicola Fameli Oluseye A. Ogunbayo Cornelis van Breemen A. Mark Evans Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q] F1000Research Cell Signaling Cell Signaling & Trafficking Structures Macromolecular Assemblies & Machines |
| title | Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q] |
| title_full | Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q] |
| title_fullStr | Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q] |
| title_full_unstemmed | Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q] |
| title_short | Cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling [v1; ref status: indexed, http://f1000r.es/32q] |
| title_sort | cytoplasmic nanojunctions between lysosomes and sarcoplasmic reticulum are required for specific calcium signaling v1 ref status indexed http f1000r es 32q |
| topic | Cell Signaling Cell Signaling & Trafficking Structures Macromolecular Assemblies & Machines |
| url | http://f1000research.com/articles/3-93/v1 |
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