Molecular mimicking of C-terminal phosphorylation tunes the surface dynamics of Ca(V)1.2 calcium channels in hippocampal neurons

L-type voltage-gated Ca(V)1.2 calcium channels (Ca(V)1.2) are key regulators of neuronal excitability, synaptic plasticity, and excitation-transcription coupling. Surface-exposed Ca(V)1.2 distributes in clusters along the dendrites of hippocampal neurons. A permanent exchange between stably clustered and laterally diffusive extra-clustered channels maintains steady-state levels of Ca(V)1.2 at dendritic signaling domains. A dynamic equilibrium between anchored and diffusive receptors is a common feature among ion channels and is crucial to modulate signaling transduction. Despite the importance of this fine regulatory system, the molecular mechanisms underlying the surface dynamics of Ca(V)1.2 are completely unexplored. Here, we examined the dynamic states of Ca(V)1.2 depending on phosphorylation on Ser-1700 and Ser-1928 at the channel C terminus. Phosphorylation at these sites is strongly involved in Ca(V)1.2-mediated nuclear factor of activated T cells (NFAT) signaling, long-term potentiation, and responsiveness to adrenergic stimulation. We engineered Ca(V)1.2 constructs mimicking phosphorylation at Ser-1700 and Ser-1928 and analyzed their behavior at the membrane by immunolabeling protocols, fluorescence recovery after photobleaching, and single particle tracking. We found that the phosphomimetic S1928E variant increases the mobility of Ca(V)1.2 without altering the steady-state maintenance of cluster in young neurons and favors channel stabilization later in differentiation. Instead, mimicking phosphorylation at Ser-1700 promoted the diffusive state of Ca(V)1.2 irrespective of the differentiation stage. Together, these results reveal that phosphorylation could contribute to the establishment of channel anchoring mechanisms depending on the neuronal differentiation state. Finally, our findings suggest a novel mechanism by which phosphorylation at the C terminus regulates calcium signaling by tuning the content of Ca(V)1.2 at signaling complexes.