The cytoplasmic interface of high voltage activated calcium channels mediates numerous interactions required for functional membrane expression. Cytoplasmic domains of the skeletal muscle DHPR ensure proper trafficking of the pore forming a_1S subunit and of its accessory b_1a subunit to triad junctions, where they couple to the Ca²⁺ release channel RyR1 and establish skeletal muscle-type excitation-contraction coupling. The precise involvement of b_1a and of the intracellular a_1S domains in these processes is obscure. In this study, we dissected the cytoplasmic interface of a_1S by expressing distinct, fluorescently labelled a_1S domains and by using confocal microscopy to determine their location within dysgenic (a_1S-null) myotubes. None of these proteins exhibited association with junctions when expressed alone. However, when the cytoplasmic a_1S domain connecting the first two homologous a_1S repeats, the I-II loop, was co-expressed with b_1a both proteins translocated and clustered at the cell surface. FRET analysis revealed that this process was accompanied by conformational changes within b_1a. Most importantly, the I-II loop peptide was able to release trafficking deficient a_1Sdel (deletion within the a_1S I-II loop) from the internal membrane compartment it was stuck to, upon ectopic mounting of b_1a to the a_1Sdel N-terminus. Co-expression of fluorescently labelled RyR1 revealed junctional co-localization with the salvaged DHPR. Our results (a) present the I-II loop as promoter of a₁ membrane expression, not as an ER retention signal, (b) reinforce b_1a's role in a_1S trafficking, whereby the I-II loop serves as conformational switch for b_1a to feed the complex into the cellular transport machinery.