Calcium Channels Gate Calcium-Independent But Voltage-Dependent Secretion in Mammalian Cells

Abstract

The somata of primary sensory neurons, including dorsal root ganglion (DRG) neurons, release neurotransmitters and neuropeptides. Following physiological action potentials, in addition to Ca2+-dependent secretion, we have discovered and studied Ca2+-independent but voltage-dependent secretion (CiVDS) in somata of freshly isolated DRG neurons. Major open question of CiVDS is the molecular mechanism, including 3 components: fusion-pore machinery, voltage-sensor and the linker of fusion-pore and voltage-sensor. Here we report, by using exocytosis assays of membrane capacitance and single vesicle imaging, CiVDS is jointly contributed by (1) SNARE protein SNAP-25 for fusion pore, (2) voltage gated Ca channel (VGCC) Cav2.2 for Ca sensor; (3) and the “synprint”, which is Cav2.2 intracellular loop718-963aa, as the linker between fusion pore and voltage sensor; (4) CiVDS presents in both somata and axons. Following automatic knockdown of CiVDS by 3d-culture of DRG neurons, CiVDS is rescued by overexpressing any component of SNAP-25 or Cav2.2. On other hand, CiVDS is inhibited by blockers against SNAP-25, Cav2.2 and synprint. CiVDS is blocked by Cav2.2-RNAi-KD in DRG pre-transfected in vivo (Chai et al, Neuron, 2017). Importantly, our recent new evidences show that CiVDS presents and functions also robustly in other essential cells, implicating that CiVDS may impact mammalian physiology and disease much more than previously thought.