Figure 6. Effect of procaine on Ca²⁺ release properties of 1B5 myotubes co-expressing α-RyR and β-RyR.

A. Representative Ca²⁺ transients induced by increasing concentrations of caffeine in the absence (Control) and presence (Procaine) of 10 mM procaine. Procaine abolished Ca²⁺ oscillations caused by exposure to lower concentrations (<5 mM) of caffeine. B. The percentage of myotubes showing Ca²⁺ oscillations at each caffeine concentration tested was plotted in reference to the number of cells responding in the presence of 20 mM caffeine. Open circles, control; filled circles, 10 mM procaine (n = 42). Procaine reduced the caffeine sensitivity. C. Representative traces of Ca²⁺ transients of myotubes induced by increasing [K⁺]_o in the absence (Control) and presence (Procaine) of 10 mM Procaine. D. Dependence of the amplitude of the Ca²⁺ transient in response to in exposure to increasing [K⁺]_o in the absence (open circles) and presence (filled circles) of 10 mM Procaine. Values represent the mean ± SE (n = 42). No statistical difference was found between the two groups at all the [K⁺]_o concentrations examined.