Calcium transients in 1B5 myotubes lacking ryanodine receptors are related to inositol trisphosphate receptors.
Potassium depolarization of skeletal myotubes evokes slow calcium waves that are unrelated to contraction and involve the cell nucleus (Jaimovich, E., Reyes, R., Liberona, J. L., and Powell, J. A. (2000) Am. J. Physiol. 278, C998-C1010). Studies were done in both the 1B5 (Ry53-/-) murine "dyspedic" myoblast cell line, which does not express any ryanodine receptor isoforms (Moore, R. A., Nguyen, H., Galceran, J., Pessah, I. N., and Allen, P. D. (1998) J. Cell Biol. 140, 843-851), and C(2)C(12) cells, a myoblast cell line that expresses all three isoforms. Although 1B5 cells lack ryanodine binding, they bind tritiated inositol (1,4,5)-trisphosphate. Both type 1 and type 3 inositol trisphosphate receptors were immuno-located in the nuclei of both cell types and were visualized by Western blot analysis. After stimulation with 47 mm K(+), inositol trisphosphate mass raised transiently in both cell types. Both fast calcium increase and slow propagated calcium signals were seen in C(2)C(12) myotubes. However, 1B5 myotubes (as well as ryanodine-treated C(2)C(12) myotubes) displayed only a long-lasting, non-propagating calcium increase, particularly evident in the nuclei. Calcium signals in 1B5 myotubes were almost completely blocked by inhibitors of the inositol trisphosphate pathway: U73122, 2-aminoethoxydiphenyl borate, or xestospongin C. Results support the hypothesis that inositol trisphosphate mediates slow calcium signals in muscle cell ryanodine receptors, having a role in their time course and propagation.
Estrada
M
M
Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Casilla 70005, Santiago 6530499, Chile.
Cárdenas
C
C
Liberona
J L
JL
Carrasco
M A
MA
Mignery
G A
GA
Allen
P D
PD
Jaimovich
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D002461:Cell Line, Transformed; D006367:HeLa Cells; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000037:antagonists & inhibitors / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D051379:Mice; D009132:Muscles / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D012433:Ryanodine / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D015398:Signal Transduction
D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium