title: Trisk 32 regulates IP(3) receptors in rat skeletal myoblasts.
abstract: To date, four isoforms of triadins have been identified in rat skeletal muscle. While the function of the 95-kDa isoform in excitation-contraction coupling has been studied in detail, the role of the 32-kDa isoform (Trisk 32) remains elusive. Here, Trisk 32 overexpression was carried out by stable transfection in L6.G8 myoblasts. Co-localization of Trisk 32 and IP(3) receptors (IP(3)R) was demonstrated by immunocytochemistry, and their association was shown by co-immunoprecipitation. Functional effects of Trisk 32 on IP(3)-mediated Ca(2+) release were assessed by measuring changes in [Ca(2+)](i) following the stimulation by bradykinin or vasopressin. The amplitude of the Ca(2+) transients evoked by 20 μM bradykinin was significantly higher in Trisk 32-overexpressing (p < 0.01; 426 ± 84 nM, n = 27) as compared to control cells (76 ± 12 nM, n = 23). The difference remained significant (p < 0.02; 217 ± 41 nM, n = 21, and 97 ± 29 nM, n = 31, respectively) in the absence of extracellular Ca(2+). Similar observations were made when 0.1 μM vasopressin was used to initiate Ca(2+) release. Possible involvement of the ryanodine receptors (RyR) in these processes was excluded, after functional and biochemical experiments. Furthermore, Trisk 32 overexpression had no effect on store-operated Ca(2+) entry, despite a decrease in the expression of STIM1. These results suggest that neither the increased activity of RyR, nor the amplification of SOCE, is responsible for the differences observed in bradykinin- or vasopressin-evoked Ca(2+) transients; rather, they were due to the enhanced activity of IP(3)R. Thus, Trisk 32 not only co-localizes with, but directly contributes to, the regulation of Ca(2+) release via IP(3)R.
authors.affiliation: Department of Physiology, Medical and Health Science Center, University of Debrecen, 4012, P.O. Box 22, Debrecen, Hungary.
authors.forename: Tamás
authors.initials: T
authors.lastname: Oláh
authors.forename: János
authors.initials: J
authors.lastname: Fodor
authors.forename: Sarah
authors.initials: S
authors.lastname: Oddoux
authors.forename: Olga
authors.initials: O
authors.lastname: Ruzsnavszky
authors.forename: Isabelle
authors.initials: I
authors.lastname: Marty
authors.forename: László
authors.initials: L
authors.lastname: Csernoch
mesh_terms: D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology*; D056966:Excitation Contraction Coupling; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000187:drug effects*; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins / Q000502:physiology*; D032448:Myoblasts, Skeletal / Q000187:drug effects / Q000378:metabolism*; D020033:Protein Isoforms / Q000502:physiology; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000502:physiology; D014667:Vasopressins / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D053496:Inositol 1,4,5-Trisphosphate Receptors; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D020033:Protein Isoforms; D019837:Ryanodine Receptor Calcium Release Channel; C498271:Trdn protein, rat; D014667:Vasopressins; D001920:Bradykinin; D002118:Calcium