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 Ca 2+ channels and voltage-gated Ca 2+ 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 Ca 2+ channel activity, the extent of caffeine-induced sarcoplasmic reticulum Ca 2+ release, or the termination kinetics of Ca 2+ transients. Thus, stimulation of VGCR cannot be explained by upregulation of the activity of either L-type Ca 2+ channels or sarcoplasmic reticulum Ca 2+-ATPase. We also investigated possible long-term regulation of L-type Ca 2+ channels by Cr. However, chronic treatment with Cr (2-4 days) affected neither the density of I CaL nor the corresponding voltage-dependence 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 Ca 2+ 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.