Creatine supplementation upregulates excitation-contraction coupling in C2C12 myotubes

Abstract:

The main goal of this work was to investigate whether creatine (Cr) might be able to regulate skeletal muscle excitation-contraction (EC) coupling. Myotubes from a C2C12 cell line were exposed to Cr (25 mM, 2–4 hours). Subsequently, the activity of L-type Ca²⁺ channels and voltage-gated Ca²⁺ release (VGCR) were investigated using the whole-cell patch-clamp technique. Cr upregulated VGCR by 2.4-fold, in the absence of major alterations in L-type Ca²⁺ channel activity, the extent of caffeine-induced sarcoplasmic reticulum Ca²⁺ release, or the termination kinetics of Ca²⁺ transients. Thus, stimulation of VGCR cannot be explained by upregulation of the activity of either L-type Ca²⁺ channels or sarcoplasmic reticulum Ca²⁺-ATPase. We also investigated possible long-term regulation of L-type Ca²⁺ channels by Cr. However, chronic treatment with Cr (2–4 days) affected neither the density of I^CaL nor the corresponding voltagedependence of activation. The later result was obtained in the face of a 1.7-fold stimulation of myogenesis. Therefore, it cannot be explained by possible desensitization of Cr metabolism. These data could suggest that the functional expression of L-type Ca²⁺ channels is not affected by prior acute stimulation of VGCR. Previous work has shown that Cr supplementation enhances muscle strength. Thus, it will be interesting to investigate whether this effect can be at least partially explained by acute stimulation of VGCR.

Keywords::

• L-type calcium channel
• ryanodine receptor
• intracellular calcium