Figure 4.

Restoration of electrically evoked contractions in dysgenic skeletal myotubes expressing GFP-α_1S and GFP-α_1C. Electrically evoked contractions obtained from myotubes expressing GFP-α_1S (Upper) and GFP-α_1C (Lower) in normal rodent Ringer (2 mM Ca²⁺, first column) and in Ca²⁺ free Ringer solution (equimolar substitution of Ca²⁺ by Mg²⁺, middle column). Removal of extracellular Ca²⁺ blocked contractions of GFP-α_1C but not of GFP-α_1S expressing cells. Recovery of electrically evoked contractions in the GFP-α_1C expressing myotube after a return to the normal rodent Ringer solution is shown (Lower, far right). Vertical scale bar: movement distance of 10 μm (GFP-α_1S expressing myotube) or 7 μm (GFP-α_1C expressing myotube). Arrows indicate the time of application of the electrical stimulus (10 ms, 80 V). Note: In the presence of extracellular Ca²⁺, contractions were never observed for either GFP-α_1A or GFP-α_1B expressing myotubes (n > 50 for each construct).