Ca²⁺ controls gating of Voltage-gated calcium channels by releasing the β2e subunit from the plasma membrane

Voltage-gated calcium (Ca_v) channels, which are regulated by membrane potential, cytosolic Ca²⁺, phosphorylation, and membrane phospholipids, govern Ca²⁺ entry into excitable cells. Ca_v channels contain a pore-forming a1 subunit, an auxiliary α2δ subunit, and a regulatory b subunit, each encoded by several genes in mammals. In addition to a domain that interacts with the α1 subunit, β2e and β2a also interact with the cytoplasmic face of the plasma membrane through an electrostatic interaction for β2e and posttranslational acylation for β2a. We found that an increase in cytosolic Ca²⁺ promoted the release of β2e from the membrane without requiring substantial depletion of the anionic phospholipid phosphatidylinositol 4,5-bisphosphate (PIP₂) from the plasma membrane. Experiments with liposomes indicated that Ca²⁺ disrupted the interaction of the β2e amino-terminal peptide with membranes containing PIP₂. Ca²⁺ binding to calmodulin (CaM) leads to CaM-mediated inactivation of Ca_v currents. Although Ca_v2.2 coexpressed with β2a required Ca²⁺-dependent activation of CaM for Ca²⁺-mediated reduction in channel activity, Ca_v2.2 coexpressed with β2e exhibited Ca²⁺-dependent inactivation of the channel even in the presence of Ca²⁺-insensitive CaM. Inducible depletion of PIP₂ reduced Ca_v2.2 currents, and in cells coexpressing β2e, but not a form that lacks the polybasic region, increased intracellular Ca²⁺ further reduced Ca_v2.2 currents. Many hormone- or neurotransmitter-activated receptors stimulate PIP₂ hydrolysis and increase cytosolic Ca²⁺; thus, our findings suggest that β2e may integrate such receptor-mediated signals to limit Ca_v activity.