Figure 6.

Effect of caffeine on [Ca²⁺]_i in isolated myotubes in the presence of Ca²⁺ channel blockers (Ni²⁺/Cd²⁺). Representative traces show the typical time course of the response to 20 mM caffeine observed in (a) wild type (+/+) myotube; (c) calpain 3-deficient (−/−) myotube, each treated with Ni²⁺/Cd²⁺. The duration of exposure to caffeine (open bars), or 50 μM Ni²⁺/100 μM Cd²⁺ (closed bars) is represented. Bar diagrams (b) and (d) summarize the peak amplitude of the [Ca²⁺]_i response of myotubes to caffeine and CPA. The responses from the wild type myotubes (+/+; b) and calpain 3-deficient myotubes (−/−; d), are shown. Fifty μM Ni²⁺/100 μM Cd²⁺ was added to the extracellular medium prior to the second application. The number of cells tested is given in brackets.