title: Junctophilin-2 in the nanoscale organisation and functional signalling of ryanodine receptor clusters in cardiomyocytes.
abstract: Signalling nanodomains requiring close contact between the plasma membrane and internal compartments, known as 'junctions', are fast communication hubs within excitable cells such as neurones and muscle. Here, we have examined two transgenic murine models probing the role of junctophilin-2, a membrane-tethering protein crucial for the formation and molecular organisation of sub-microscopic junctions in ventricular muscle cells of the heart. Quantitative single-molecule localisation microscopy showed that junctions in animals producing above-normal levels of junctophilin-2 were enlarged, allowing the re-organisation of the primary functional protein within it, the ryanodine receptor (RyR; in this paper, we use RyR to refer to the myocardial isoform RyR2). Although this change was associated with much enlarged RyR clusters that, due to their size, should be more excitable, functionally it caused a mild inhibition in the Ca2+signalling output of the junctions (Ca2+sparks). Analysis of the single-molecule densities of both RyR and junctophilin-2 revealed an ∼3-fold increase in the junctophilin-2 to RyR ratio. This molecular rearrangement is compatible with direct inhibition of RyR opening by junctophilin-2 to intrinsically stabilise the Ca2+signalling properties of the junction and thus the contractile function of the cell.
authors: Department of Physiology, School of Medical Sciences, University of Auckland, 1023, New Zealand.
authors: Michelle L
authors: 0000-0003-0089-3956
authors: ML
authors: Munro
authors: School of Physics, University of Exeter, Exeter EX4 4QL, UK.|School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK.
authors: Izzy
authors: I
authors: Jayasinghe
authors: Cardiovascular Research Institute, Departments of Molecular Physiology and Biophysics, Medicine (Cardiology), and Pediatrics (Cardiology), Baylor College of Medicine, Houston, TX 77030, USA.
authors: Qiongling
authors: Q
authors: Wang
authors: Cardiovascular Research Institute, Departments of Molecular Physiology and Biophysics, Medicine (Cardiology), and Pediatrics (Cardiology), Baylor College of Medicine, Houston, TX 77030, USA.
authors: Ann
authors: A
authors: Quick
authors: Cardiovascular Research Institute, Departments of Molecular Physiology and Biophysics, Medicine (Cardiology), and Pediatrics (Cardiology), Baylor College of Medicine, Houston, TX 77030, USA.
authors: Wei
authors: W
authors: Wang
authors: Department of Cell Biology, Yale University, New Haven, CT 06520, USA.
authors: David
authors: D
authors: Baddeley
authors: Cardiovascular Research Institute, Departments of Molecular Physiology and Biophysics, Medicine (Cardiology), and Pediatrics (Cardiology), Baylor College of Medicine, Houston, TX 77030, USA.
authors: Xander H T
authors: XH
authors: Wehrens
authors: Department of Physiology, School of Medical Sciences, University of Auckland, 1023, New Zealand c.soeller@exeter.ac.uk.|School of Physics, University of Exeter, Exeter EX4 4QL, UK.
authors: Christian
authors: 0000-0002-9302-2203
authors: C
authors: Soeller
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D009124:Muscle Proteins / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D049329:Nanostructures / Q000737:chemistry*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D008565:Membrane Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C000589042:JP2 protein, mouse
keywords: Ca2+ signalling; Excitation-contraction coupling; Junctophilin-2; Ryanodine receptor; Super-resolution imaging; dSTORM