Figure 6. The increased resting cytosolic Ca²⁺ levels and the reduced response to KCl or caffeine by full-length MG53 or PRY-SPRY.

(a) The resting cytosolic Ca²⁺ levels in the myotubes over-expressing full-length MG53 or PRY-SPRY were measured. (b) To measure the releasable Ca²⁺ from the SR to the cytosol, TG (2.5 μM) was applied to the myotubes in the absence of extracellular Ca²⁺. The results are presented as the mean ± S.E. for the number of myotubes shown in the parenthesis in Table 1. KCl that is a membrane depolarizer and induces skeletal muscle contraction (c), or caffeine that is a specific and direct RyR1agonist (d), was applied to the myotubes over-expressing full-length MG53 or PRY-SPRY. A representative trace for each group is shown, and bar graphs of the peak amplitude normalized to the mean value of those from the vector controls are shown in the right-hand panels. The results are presented as the mean ± S.E. for the number of myotubes shown in the parenthesis in Table 1. *Significant difference versus Vector control (p < 0.05).