title: Reduced gain of excitation-contraction coupling in triadin-null myotubes is mediated by the disruption of FKBP12/RyR1 interaction.
abstract: Several studies have suggested that triadin (Tdn) may be a critical component of skeletal EC-coupling. However, using Tdn-null mice we have shown that triadin ablation results in no significant disruption of skeletal EC-coupling. To analyze the role of triadin in EC-coupling signaling here we used whole-cell voltage clamp and simultaneous recording of intracellular Ca²+ release to characterize the retrograde and orthograde signaling between RyR1 and DHPR in cultured myotubes. DHPR Ca²+ currents elicited by depolarization of Wt and Tdn-null myotubes displayed similar current densities and voltage dependence. However, kinetic analysis of the Ca²+ current shows that activation time constant of the slow component was slightly decreased in Tdn-null cells. Voltage-evoked Ca²+ transient of Tdn-null myotubes showed small but significant reduction in peak fluorescence amplitude but no differences in voltage dependence. This difference in Ca²+ amplitude was averted by over-expression of FKBP12.6. Our results show that bi-directional signaling between DHPR and RyR1 is preserved nearly intact in Tdn-null myotubes and that the effect of triadin ablation on Ca²+ transients appears to be secondary to the reduced FKBP12 binding capacity of RyR1 in Tdn-null myotubes. These data suggest that skeletal triadins do not play a direct role in skeletal EC-coupling.
authors.affiliation: Department of Anesthesiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Jose M
authors.initials: JM
authors.lastname: Eltit
authors.forename: John
authors.initials: J
authors.lastname: Szpyt
authors.forename: Hongli
authors.initials: H
authors.lastname: Li
authors.forename: Paul D
authors.initials: PD
authors.lastname: Allen
authors.forename: Claudio F
authors.initials: CF
authors.lastname: Perez
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D056966:Excitation Contraction Coupling / Q000502:physiology*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009124:Muscle Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D015398:Signal Transduction; D022061:Tacrolimus Binding Protein 1A / Q000378:metabolism*
chemical_list: C529218:CACNA1S protein, mouse; D020746:Calcium Channels, L-Type; D002352:Carrier Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C070048:triadin; D022061:Tacrolimus Binding Protein 1A; D002118:Calcium