Retrograde regulation of store-operated calcium channels by the ryanodine receptor-associated protein triadin 95 in rat skeletal myotubes.
The 95kDa triadin (or T95), the main skeletal muscle triadin isoform, negatively regulates the mechanism of excitation-contraction coupling. T95 is a ryanodine receptor (RyR)-interacting protein but it also possesses a calsequestrin-interacting domain. RyR and calsequestrin are involved in Ca2+ signalling and, for instance, influence the activity of store-dependent Ca2+ channels (SOC). This work was undertaken to determine whether T95 was able to modulate the entry of Ca2+ through SOC. The experiments were carried out on differentiated rat myotubes over-expressing T95 or DsRed (control cells) by means of an adenovirus infection. Intracellular Ca2+ signals were analyzed using the Ca2+ indicator Fluo-4. The sarco-endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin was used to deplete intracellular Ca2+ stores. When applied in the presence of a Ca2+-free medium, thapsigargin elicited transient but long-lasting Fluo-4 responses by elevating the cytoplasmic concentration of Ca2+ ([Ca2+]i). The over-expression of T95 reduced the thapsigargin-dependent [Ca2+]i increase, with respect to control myotubes. Addition of extracellular Ca2+after the depletion of this Ca2+ pool was accompanied by a [Ca2+]i increase that was sensitive to the SOC blockers 2-APB, SKF-96365 and La3+. The over-expression of T95 reduced this Ca2+ influx, without changing its pharmacological properties, showing that T95 over-expression did not alter the properties of the SOC. In conclusion, the RyR-interacting molecule T95, recently shown to inhibit the excitation-contraction coupling, has also the ability to interfere with the skeletal muscle Ca2+ signalling by depressing thapsigargin-dependent Ca2+ release and influx.
Vassilopoulos
Stéphane
S
Inserm U607, 17 rue des Martyrs, 38054 Grenoble, France.
Brocard
Julie
J
Garcia
Luis
L
Marty
Isabelle
I
Bouron
Alexandre
A
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism* / Q000502:physiology; D005786:Gene Expression Regulation; D047908:Intracellular Signaling Peptides and Proteins; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology
D015220:Calcium Channels; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; C498271:Trdn protein, rat; D019284:Thapsigargin; D002118:Calcium