title: Triadin overexpression stimulates excitation-contraction coupling and increases predisposition to cellular arrhythmia in cardiac myocytes.
abstract: Triadin 1 (TRD) is an integral membrane protein that associates with the ryanodine receptor (RyR2), calsequestrin (CASQ2) and junctin to form a macromolecular Ca signaling complex in the cardiac junctional sarcoplasmic reticulum (SR). To define the functional role of TRD, we examined the effects of adenoviral-mediated overexpression of the wild-type protein (TRD(WT)) or a TRD mutant lacking the putative CASQ2 interaction domain residues 200 to 224 (TRD(Del.200-224)) on intracellular Ca signaling in adult rat ventricular myocytes. Overexpression of TRD(WT) reduced the amplitude of I(Ca)- induced Ca transients (at 0 mV) but voltage dependency of the Ca transients was markedly widened and flattened, such that even small I(Ca) at low and high depolarizations triggered maximal Ca transients. The frequency of spontaneous Ca sparks was significantly increased in TRD(WT) myocytes, whereas the amplitude of individual sparks was reduced. Consistent with these changes in Ca release signals, SR Ca content was decreased in TRD(WT) myocytes. Periodic electrical stimulation of TRD(WT) myocytes resulted in irregular, spontaneous Ca transients and arrhythmic oscillations of the membrane potential. Expression of TRD(Del.200-224) failed to produce any of the effects of the wild-type protein. The lipid bilayer technique was used to record the activity of single RyR2 channels using microsome samples obtained from control, TRD(WT) and TRD(Del.200-224) myocytes. Elevation of TRD(WT) levels increased the open probability of RyR2 channels, whereas expression of the mutant protein did not affect RyR2 activity. We conclude that TRD enhances cardiac excitation-contraction coupling by directly stimulating the RyR2. Interaction of TRD with RyR2 may involve amino acids 200 to 224 in C-terminal domain of TRD.
authors.affiliation: Department of Physiology and Cell Biology, Heart and Lung Research Institute, Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Terentyev
authors.forename: Steven E
authors.initials: SE
authors.lastname: Cala
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Houle
authors.forename: Serge
authors.initials: S
authors.lastname: Viatchenko-Karpinski
authors.forename: Inna
authors.initials: I
authors.lastname: Gyorke
authors.forename: Radmila
authors.initials: R
authors.lastname: Terentyeva
authors.forename: Simon C
authors.initials: SC
authors.lastname: Williams
authors.forename: Sandor
authors.initials: S
authors.lastname: Gyorke
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000503:physiopathology*; D002118:Calcium / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D004285:Dogs; D004558:Electric Stimulation; D015870:Gene Expression; D005822:Genetic Vectors / Q000235:genetics; D047908:Intracellular Signaling Peptides and Proteins; D015640:Ion Channel Gating / Q000502:physiology; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008297:Male; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000502:physiology; D008861:Microsomes / Q000502:physiology; D006899:Mixed Function Oxygenases / Q000502:physiology; D008955:Models, Cardiovascular; D009124:Muscle Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000502:physiology* / Q000648:ultrastructure; D017434:Protein Structure, Tertiary; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014161:Transduction, Genetic
chemical_list: D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008565:Membrane Proteins; D009124:Muscle Proteins; D011993:Recombinant Fusion Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C498269:TRDN protein, human; C498271:Trdn protein, rat; C503872:caisequestrin 2, rat; C070048:triadin; D006899:Mixed Function Oxygenases; D002118:Calcium