Ca2+ controls gating of voltage-gated calcium channels by releasing the beta 2e subunit from the plasma membrane

Abstract

Voltage-gated calcium (Cav) channels, which are regulated by membrane potential, cytosolic Ca2+, phosphorylation, and membrane phospholipids, govern Ca2+ entry into excitable cells. Cav 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 Cav currents. Although Cav2.2 coexpressed with β2a required Ca2+-dependent activation of CaM for Ca2+-mediated reduction in channel activity, Cav2.2 coexpressed with β2e exhibited Ca2+-dependent inactivation of the channel even in the presence of Ca2+-insensitive CaM. Inducible depletion of PIP2 reduced Cav2.2 currents, and in cells coexpressing β2e, but not a form that lacks the polybasic region, increased intracellular Ca2+ further reduced Cav2.2 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 Cav activity.