Ca²⁺ influx via the L-type channel accounts for the bulk of Ca²⁺ influx in response to depolarization. Representative Ca²⁺ transients are shown for a normal myotube in 2 mM of bath Ca²⁺ (A), a normal myotube in nominal 0 mM of bath Ca²⁺ (B), a dysgenic myotube expressing SkEIIIK in 2 mM Ca²⁺ (C), and a dysgenic myotube expressing SkEIIIK in 0 mM Ca²⁺ (D). Summary of t_{1/2 decay} (E) and r₂₀ (F) values for normal myotubes and dysgenic myotubes expressing SkEIIIK in the presence (solid bars) and absence (hatched bars) of 2 mM Ca²⁺. In B–D, a scaled version of the transient shown in A has been included for comparison of the rates of transient decay (gray traces). Transients were elicited locally by 20-s applications of 80 mM KCl via micropipette placed close to the myotube of interest. See Materials and methods for definitions of t_{1/2 decay} and r₂₀. Asterisks indicate a significant difference (P < 0.0005, ANOVA).