FIGURE 4.

The slow calcium signal is blocked by TTX and is refractory to ryanodine. The myotubes were exposed to 400 pulses of 1 ms at 45 Hz. (A) The experiments were performed in normal saline with calcium (solid circles) and 10 μM TTX (solid squares). The mean of at least seven independent experiments ± SE is shown. (B) The fluorescence signals after the exposure to 10 μM (open squares) and 30 μM (open circles) of ryanodine, and the control condition without extracellular calcium (0.5 mM EGTA, open triangles), are shown. The mean of at least 10 independent experiments ± SE is shown. The lower trace shows the timing of the stimulation protocol.