title: Dampened activity of ryanodine receptor channels in mutant skeletal muscle lacking TRIC-A.
abstract: The role of trimeric intracellular cation (TRIC) channels is not known, although evidence suggests they may regulate ryanodine receptors (RyR) via multiple mechanisms. We therefore investigated whether Tric-a gene knockout (KO) alters the single-channel function of skeletal RyR (RyR1). We find that RyR1 from Tric-a KO mice are more sensitive to inhibition by divalent cations, although they respond normally to cytosolic Ca2+, ATP, caffeine and luminal Ca2+. In the presence of Mg2+, ATP cannot effectively activate RyR1 from Tric-a KO mice. Additionally, RyR1 from Tric-a KO mice are not activated by protein kinase A phosphorylation, demonstrating a defect in the ability of β-adrenergic stimulation to regulate sarcoplasmic reticulum (SR) Ca2+-release. The defective RyR1 gating that we describe probably contributes significantly to the impaired SR Ca2+-release observed in skeletal muscle from Tric-a KO mice, further highlighting the importance of TRIC-A for normal physiological regulation of SR Ca2+-release in skeletal muscle.
  
  
  
  The type A trimeric intracellular cation channel (TRIC-A) is a major component of the nuclear and sarcoplasmic reticulum (SR) membranes of cardiac and skeletal muscle, and is localized closely with ryanodine receptor (RyR) channels in the SR terminal cisternae. The skeletal muscle of Tric-a knockout (KO) mice is characterized by Ca2+overloaded and swollen SR and by changes in the properties of SR Ca2+release. We therefore investigated whether RyR1 gating behaviour is modified in the SR from Tric-a KO mice by incorporating native RyR1 into planar phospholipid bilayers under voltage-clamp conditions. We find that RyR1 channels from Tric-a KO mice respond normally to cytosolic Ca2+, ATP, adenine, caffeine and to luminal Ca2+. However, the channels are more sensitive to the inactivating effects of divalent cations, thus, in the presence of Mg2+, ATP is inadequate as an activator. Additionally, channels are not characteristically activated by protein kinase A even though the phosphorylation levels of Ser2844 are similar to controls. The results of the present study suggest that TRIC-A functions as an excitatory modulator of RyR1 channels within the SR terminal cisternae. Importantly, this regulatory action of TRIC-A appears to be independent of (although additive to) any indirect consequences to RyR1 activity that arise as a result of K+fluxes across the SR via TRIC-A.
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Sam
authors.initials: S
authors.lastname: El-Ajouz
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Elisa
authors.initials: E
authors.lastname: Venturi
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Katja
authors.initials: K
authors.lastname: Witschas
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Beech
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Abigail D
authors.initials: AD
authors.lastname: Wilson
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.|Department of Chemistry, University of Oxford, Oxford, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Lindsay
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: David
authors.initials: D
authors.lastname: Eberhardt
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Fiona
authors.initials: F
authors.lastname: O'Brien
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Tsunaki
authors.initials: T
authors.lastname: Iida
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Miyuki
authors.initials: M
authors.lastname: Nishi
authors.affiliation: Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takeshima
authors.affiliation: Department of Pharmacology, University of Oxford, Oxford, UK.
authors.forename: Rebecca
authors.identifier: 0000-0002-3216-2560
authors.initials: R
authors.lastname: Sitsapesan
mesh_terms: D000225:Adenine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D003412:Cricetulus; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D003600:Cytosol / Q000502:physiology; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D008274:Magnesium / Q000494:pharmacology; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000502:physiology*; D009154:Mutation; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology*
chemical_list: D007473:Ion Channels; D019837:Ryanodine Receptor Calcium Release Channel; C522221:TRIC-A protein, mouse; C000592747:ryanodine receptor 1, mouse; D002110:Caffeine; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D008274:Magnesium; D000225:Adenine; D002118:Calcium
keywords: Ca2+ release; ryanodine receptor; sarcoplasmic reticulum