RIM1 confers sustained activity and neurotransmitter vesicle anchoring to presynaptic Ca²⁺ channels

The molecular organization of presynaptic active zones is important for the neurotransmitter release that is triggered by depolarization-induced Ca ²⁺ influx. Here, we demonstrate a previously unknown interaction between two components of the presynaptic active zone, RIM1 and voltage-dependent Ca²⁺ channels (VDCCs), that controls neurotransmitter release in mammalian neurons. RIM1 associated with VDCC β-subunits via its C terminus to markedly suppress voltage-dependent inactivation among different neuronal VDCCs. Consistently, in pheochromocytoma neuroendocrine PC12 cells, acetylcholine release was significantly potentiated by the full-length and C-terminal RIM1 constructs, but membrane docking of vesicles was enhanced only by the full-length RIM1. The β construct beta-AID dominant negative, which disrupts the RIM1-β association, accelerated the inactivation of native VDCC currents, suppressed vesicle docking and acetylcholine release in PC12 cells, and inhibited glutamate release in cultured cerebellar neurons. Thus, RIM1 association with β in the presynaptic active zone supports release via two distinct mechanisms: sustaining Ca²⁺ influx through inhibition of channel inactivation, and anchoring neurotransmitter-containing vesicles in the vicinity of VDCCs.