Time course of the activation of Ca_V1.1 and R Y R1 channels. (A) Membrane current from Ca_V1.1 channels expressed in Xenopus oocytes displaying gating (gray) and ionic currents (red). (A and B) The rearrangement of Ca_V1.1 voltage sensors upon depolarization (gating currents, gray) activates two processes with very distinct kinetics: Ca_V1.1 ionic current (slow; red in A) and SR Ca²⁺ release (fast; in B) from dissociated mouse muscle fibers (flexor digitorum brevis) loaded with the Ca²⁺ dye OGB-5N. Recordings are shown on the same time scale to illustrate their drastically different kinetics.