Figure 5.
Excitation-contraction coupling is abolished by streptavidin binding to the proximal portion of the α1S II-III loop, but is unaffected when binding occurs at the α1S N terminus or β1a N or C terminus. Electrically evoked contractions are shown for intact β1-null myotubes expressing YFP-β1a-BAD or BAD-β1a-YFP, or dysgenic myotubes expressing BAD-α1S-YFP or α1S(671-BAD-686)-YFP. Prior to streptavidin injection, myotubes responded to extracellular stimulation with robust contractions (top). 2–4 h after streptavidin injection, the same individual myotubes were tested for their responses to identical stimulation (bottom). Vertical scale, arbitrary units. For BAD-β1a-YFP–expressing cells, streptavidin binding following injection has not yet been confirmed by confocal imaging.