Ca β controls the endocytic turnover of Ca 1.2 L-type calcium channel.

Membrane depolarization activates the multisubunit Ca 1.2 L-type calcium channel initiating various excitation coupling responses. Intracellular trafficking into and out of the plasma membrane regulates the channel's surface expression and stability, and thus, the strength of Ca 1.2-mediated Ca signals. The mechanisms regulating the residency time of the channel at the cell membrane are unclear. Here, we coexpressed the channel core complex Ca 1.2α pore-forming and auxiliary Ca β subunits and analyzed their trafficking dynamics from single-particle-tracking trajectories. Speed histograms obtained for each subunit were best fitted to a sum of diffusive and directed motion terms. The same mean speed for the highest-mobility state underlying directed motion was found for all subunits. The frequency of this component increased by covalent linkage of Ca β to Ca 1.2α suggesting that high-speed transport occurs in association with Ca β. Selective tracking of Ca 1.2α along the postendocytic pathway failed to show the highly mobile state, implying Ca β-independent retrograde transport. Retrograde speeds of Ca 1.2α are compatible with myosin VI-mediated backward transport. Moreover, residency time at the cell surface was significantly prolonged when Ca 1.2α was covalently linked to Ca β. Thus, Ca β promotes fast transport speed along anterograde trafficking and acts as a molecular switch controlling the endocytic turnover of L-type calcium channels.