A Possible Role of Kainate Receptors in C2C12 Skeletal Myogenic Cells

ABSTRACT

Ca2+ influx appears to be important for triggering myoblast fusion. It remains, however, unclear how Ca2+ influx rises prior to myoblast fusion. Recently, several studies suggested that NMDA receptors may be involved in Ca2+ mobilization of muscle, and that Ca2+ influx is mediated by NMDA receptors in C2C12 myoblasts. Here, we report that other types of ionotropic glutamate receptors, non-NMDA receptors (AMPA and KA receptors), are also involved in Ca2+ influx in myoblasts. To explore which subtypes of non-NMDA receptors are expressed in C2C12 myogenic cells, RT-PCR was performed, and the results revealed that KA receptor subunits were expressed in both myoblasts and myotubes. However, AMPA receptor was not detected in myoblasts but expressed in myotubes. Using a Ca2+ imaging system, Ca2+ influx mediated by these receptors was directly measured in a single myoblast cell. Intracellular Ca2+ level was increased by KA, but not by AMPA. These results were consistent with RT-PCR data. In addition, KA-induced intracellular Ca2+ increase was completely suppressed by treatment of nifedifine, a L-type Ca2+ channel blocker. Furthermore, KA stimulated myoblast fusion in a dose-dependent manner. CNQX inhibited not only KA-induced myoblast fusion but also spontaneous myoblast fusion. Therefore, these results suggest that KA receptors are involved in intracellular Ca2+ increase in myoblasts and then may play an important role in myoblast fusion.