FIGURE 2.

Quantitation and kinetics of calcium transients evoked by ATP in skeletal myotubes. ATP increases intracellular Ca²⁺ in a concentration-dependent manner in skeletal myotubes. Cells were incubated with 0.001 μm-1 mm ATP, and calcium transients were measured as described in the legend for Fig. 2. From the calcium signals we analyzed the maximal fluorescence reached (A), the percentage of activated cells (B), and the time to peak (C). Values were expressed as mean ± S.E. Each coverslip was used to assay only one ATP concentration. Each bar represents values obtained in 12–25 cells from three independent coverslips.