title: Sensitized signalling between L-type Ca2+ channels and ryanodine receptors in the absence or inhibition of FKBP12.6 in cardiomyocytes.
abstract: The heart contraction is controlled by the Ca2+-induced Ca2+ release (CICR) between L-type Ca2+ channels and ryanodine receptors (RyRs). The FK506-binding protein FKBP12.6 binds to RyR subunits, but its role in stabilizing RyR function has been debated for long. Recent reports of high-resolution RyR structure show that the HD2 domain that binds to the SPRY2 domain of neighbouring subunit in FKBP-bound RyR1 is detached and invisible in FKBP-null RyR2. The present study was to test the consequence of FKBP12.6 absence on the in situ activation of RyR2.
  
  
  
  Using whole-cell patch-clamp combined with confocal imaging, we applied a near threshold depolarization to activate a very small fraction of LCCs, which in turn activated RyR Ca2+ sparks stochastically. FKBP12.6-knockout and FK506/rapamycin treatments increased spark frequency and LCC-RyR coupling fidelity without altering LCC open probability. Neither FK506 nor rapamycin further altered LCC-RyR coupling fidelity in FKBP12.6-knockout cells. In loose-seal patch-clamp experiments, the LCC-RyR signalling kinetics, indexed by the delay for a LCC sparklet to trigger a RyR spark, was accelerated after FKBP12.6 knockout and FK506/rapamycin treatments. These results demonstrated that RyRs became more sensitive to Ca2+ triggers without FKBP12.6. Isoproterenol (1 μM) further accelerated the LCC-RyR signalling in FKBP12.6-knockout cells. The synergistic sensitization of RyRs by catecholaminergic signalling and FKBP12.6 dysfunction destabilized the CICR system, leading to chaotic Ca2+ waves and ventricular arrhythmias.
  
  
  
  FKBP12.6 keeps the RyRs from over-sensitization, stabilizes the potentially regenerative CICR system, and thus may suppress the life-threatening arrhythmogenesis.
authors.affiliation: State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Road, Beijing 100871, China.
authors.forename: Yan-Ting
authors.initials: YT
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Road, Beijing 100871, China.
authors.forename: Yun-Bo
authors.initials: YB
authors.lastname: Guo
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Gu
authors.affiliation: State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Road, Beijing 100871, China.
authors.forename: Xue-Xin
authors.initials: XX
authors.lastname: Fan
authors.affiliation: State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Road, Beijing 100871, China.
authors.forename: Hua-Qian
authors.initials: HQ
authors.lastname: Yang
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Road, Beijing 100871, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhou
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Yuan
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing 100101, China.
authors.forename: Guang-Ju
authors.initials: GJ
authors.lastname: Ji
authors.affiliation: State Key Laboratory of Membrane Biology, College of Life Sciences, Peking University, 5 Yiheyuan Road, Beijing 100871, China.
authors.forename: Shi-Qiang
authors.initials: SQ
authors.lastname: Wang
mesh_terms: D000818:Animals; D001145:Arrhythmias, Cardiac / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology / Q000517:prevention & control; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects; D005838:Genotype; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D008958:Models, Molecular; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010641:Phenotype; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020239:Receptor Cross-Talk / Q000187:drug effects; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology; D013269:Stochastic Processes; D016559:Tacrolimus / Q000494:pharmacology; D022021:Tacrolimus Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics
chemical_list: D020746:Calcium Channels, L-Type; D007545:Isoproterenol; D019837:Ryanodine Receptor Calcium Release Channel; D020123:Sirolimus; D016559:Tacrolimus; D022021:Tacrolimus Binding Proteins; C509259:FKBP1B protein, mouse; C000592748:ryanodine receptor 2. mouse
keywords: Calcium signalling; Excitation-contraction coupling; FK506-binding protein; Ryanodine receptor