Jcb_201304101 1..17

Exocytosis in response to action potential–evoked membrane depolarization has been extensively characterized in the nervous system, in which neurotransmitters or hormones are released after extracellular Ca influx at synapses in neurons or in neuroendocrine cells, respectively. In pancreatic islet  cells, for example, glucose elevation results in the closure of KATP channels, membrane depolarization, opening of voltage-gated calcium channels (VGCCs), and, in response to Ca influx, secretion of insulin (Yang and Berggren, 2006). At neuronal synapses, neurotransmitter-containing vesicles are docked in close vicinity to VGCCs at the presynaptic active zone (Neher, 1998; Zhai and Bellen, 2004; Atwood, 2006). Although the spatial proximity of VGCCs and exocytic vesicles undergoing fusion with the plasma membrane is well documented, the detailed molecular mechanisms involved in the spatial and temporal coupling of exocytosis and VGCC activation and inactivation remain to be elucidated. VGCCs are composed of an ion pore–forming Cav1 subunit associated with several auxiliary subunits (Cav, Cav2, and Cav; Arikkath and Campbell, 2003). Among the Cav1 subunits, the P/Q-type Cav2.1 and the N-type Cav2.2 define the main channel subtypes important for presynaptic neurotransmitter release (Spafford and Zamponi, 2003; Evans and Zamponi, 2006), and the L-type Cav1.2 subtype triggers Ca-dependent secretion in neuroendocrine cells (Catterall, 2000). Four Cav subunit isoforms Voltage-gated calcium channels (VGCCs) are key regulators of cell signaling and Ca-dependent release of neurotransmitters and hormones. Understanding the mechanisms that inactivate VGCCs to prevent intracellular Ca overload and govern their specific subcellular localization is of critical importance. We report the identification and functional characterization of VGCC -anchoring and -regulatory protein (BARP), a previously uncharacterized integral membrane glycoprotein expressed in neuroendocrine cells and neurons. BARP interacts via two cytosolic domains (I and II) with all Cav subunit isoforms, affecting their subcellular localization and suppressing VGCC activity. Domain I interacts at the 1 interaction domain–binding pocket in Cav and interferes with the association between Cav and Cav1. In the absence of domain I binding, BARP can form a ternary complex with Cav1 and Cav via domain II. BARP does not affect cell surface expression of Cav1 but inhibits Ca channel activity at the plasma membrane, resulting in the inhibition of Ca-evoked exocytosis. Thus, BARP can modulate the localization of Cav and its association with the Cav1 subunit to negatively regulate VGCC activity. BARP suppresses voltage-gated calcium channel activity and Ca2+-evoked exocytosis