Figure 2

Absence of EC coupling in non-transfected dysgenic myotubes. The confocal line-scan images in color show fluo-4 fluorescence across myotubes in response to a 50-ms depolarization from a holding potential of -40 mV. Line scan images have a constant temporal dimension of 2.05 s (horizontal) and a variable spatial dimension (vertical) depending on the cell size. Traces immediately above each line scan show the time course of the fluorescence change in resting units (ΔF/Fo). The amplitude and the timing of the depolarization are indicated under each line-scan. Arrow indicates a small Ca²⁺ transient elicited in 1 of 2 cells found to express Idys. Traces next to lines-cans show ICa²⁺ during the 50 ms depolarization used to stimulate the Ca²⁺ transient. Current calibration bars are 10 ms and 1 pA/pF. A) Absence of Ca²⁺ transients and ICa²⁺ in a typical dysgenic cell. B) Minor Ca²⁺ transient and ICa²⁺ in a cell expressing Idys. Note that fluorescence calibration bar is 0.5 ΔF/Fo. A 16-color calibration bar in ΔF/Fo units is included in Fig. 3 for visual reference. C) Voltage dependence of the mean (± SEM) ICa²⁺ and mean peak Ca²⁺ transient (± SEM) in 13 cells not expressing ICa²⁺ and 2 cells expressing Idys (mean only).