Calcium Ionophore Inhibits GSK‐3[beta] in Cultured Myotubes via a Nitric Oxide‐Dependent Mechanism

Glycogen synthase kinase (GSK)‐3β inhibits glycogen storage, protein synthesis, and has recently been shown to inhibit the calcineurin‐dependent transcriptional effects of nuclear factor of activated T‐cells (NFAT) by re‐phosphorylation and subsequent exclusion from the nucleus. We hypothesized that calcium may facilitate adaptive responses in skeletal muscle cells by inhibiting GSK‐3β. Further, this effect may be mediated by the signaling molecule nitric oxide (NO). Methods: C2C12 cells were seeded on 6 well plates and incubated in 10% Fetal Bovine Serum and changed to 2% Horse Serum at 5 days to induce differentiation. Myotubes were grown to 80% confluency and were treated with calcium ionophore A23187, L‐NAME, A23187 + L‐NAME, or PAPA‐NO. Protein lysates were separated by SDS‐PAGE and quantified by immunoblot. Results: GSK‐3β phosphorylation status (p‐GSK/total GSK) was increased by A23187 in a dose‐dependent manner, indicating an inhibiting effect. L‐NAME treatment alone did not affect baseline phosphorylation of GSK‐3β. However, co‐treatment with L‐NAME completely inhibited the A23187‐induced phosphorylation of GSK‐3β, demonstrating the necessity of NO for the A23187 effect. Further, PAPA‐NO treated cells increased p‐GSK/total GSK by 50% compared to control. GSK‐3β inhibition via calcium is, therefore, dependent on NO levels in myocytes.