title: Abnormal termination of Ca2+ release is a common defect of RyR2 mutations associated with cardiomyopathies.
abstract: BACKGROUND
  Naturally occurring mutations in the cardiac ryanodine receptor (RyR2) have been associated with both cardiac arrhythmias and cardiomyopathies. It is clear that delayed afterdepolarization resulting from abnormal activation of sarcoplasmic reticulum Ca2+ release is the primary cause of RyR2-associated cardiac arrhythmias. However, the mechanism underlying RyR2-associated cardiomyopathies is completely unknown.
  
  
  OBJECTIVE
  In the present study, we investigate the role of the NH2-terminal region of RyR2 in and the impact of a number of cardiomyopathy-associated RyR2 mutations on the termination of Ca2+ release.
  
  
  RESULTS
  The 35-residue exon-3 region of RyR2 is associated with dilated cardiomyopathy. Single-cell luminal Ca2+ imaging revealed that the deletion of the first 305 NH2-terminal residues encompassing exon-3 or the deletion of exon-3 itself markedly reduced the luminal Ca2+ threshold at which Ca2+ release terminates and increased the fractional Ca2+ release. Single-cell cytosolic Ca2+ imaging also showed that both RyR2 deletions enhanced the amplitude of store overload-induced Ca2+ transients in HEK293 cells or HL-1 cardiac cells. Furthermore, the RyR2 NH2-terminal mutations, A77V, R176Q/T2504M, R420W, and L433P, which are associated with arrhythmogenic right ventricular displasia type 2, also reduced the threshold for Ca2+ release termination and increased fractional release. The RyR2 A1107M mutation associated with hypertrophic cardiomyopathy had the opposite action (i.e., increased the threshold for Ca2+ release termination and reduced fractional release).
  
  
  CONCLUSIONS
  These results provide the first evidence that the NH2-terminal region of RyR2 is an important determinant of Ca2+ release termination, and that abnormal fractional Ca2+ release attributable to aberrant termination of Ca2+ release is a common defect in RyR2-associated cardiomyopathies.
authors.affiliation: Department of Physiology and Pharmacology, the Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, AB, Canada.
authors.forename: Yijun
authors.initials: Y
authors.lastname: Tang
authors.forename: Xixi
authors.initials: X
authors.lastname: Tian
authors.forename: Ruiwu
authors.initials: R
authors.lastname: Wang
authors.forename: Michael
authors.initials: M
authors.lastname: Fill
authors.forename: S R Wayne
authors.initials: SR
authors.lastname: Chen
mesh_terms: D000818:Animals; D019571:Arrhythmogenic Right Ventricular Dysplasia / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D009202:Cardiomyopathies / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D002478:Cells, Cultured; D005091:Exons / Q000235:genetics; D017353:Gene Deletion; D049452:Green Fluorescent Proteins / Q000235:genetics; D057809:HEK293 Cells; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D051379:Mice; D023421:Models, Animal; D009154:Mutation / Q000235:genetics*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014162:Transfection
chemical_list: D019837:Ryanodine Receptor Calcium Release Channel; D049452:Green Fluorescent Proteins; D002118:Calcium