NEUROTRANSMISSION That Had Spontaneously Reduced Nature Reviews

RESEARCH HIGHLIGHTS

Nature Reviews Neuroscience | Published online 14 Dec 2017; doi:10.1038/nrn.2017.162

(SNARE) complex, as this mediates Ca2+-dependent vesicle fusion in CDS. In line with this hypothesis, CiVDS was inhibited in DRG neurons by application of a combination of SNARE-protein-cleaving toxins. Furthermore, co-immunoprecipi-

tation revealed that CaV2.2 in DRG neurons physically interacts with SNAP25, a SNARE protein. These Jennie Vallis/Macmillan Publishers Limited Jennie Vallis/Macmillan results prompted the authors to ask

whether CaV2.2 might bind directly to the SNARE complex to enable CiVDS. They truncated the synaptic protein interaction (synprint) site

of CaV2.2; this synprint-truncated

CaV2.2 did not bind SNAP25 and did not rescue CiVDS in DRG neurons NEUROTRANSMISSION that had spontaneously reduced Nature Reviews | Neuroscience CiVDS. Thus, the CaV2.2 synprint A discrete form of secretion site links the voltage-sensing function of the channel with the SNARE machinery to enable CiVDS. Action potentials trigger the influx by depolarization in a Ca2+-free What is the cargo released during of Ca2+ ions through voltage-gated solution — in freshly isolated mouse CiVDS? A luciferase–luciferin calcium channels, which in turn leads DRG neurons. CiVDS was strongly assay demonstrated that ATP is to Ca2+-dependent secretion (CDS) of inhibited by an antagonist of N-type released from depolarized neurons vesicles containing neurotransmitters voltage-gated calcium channels in Ca2+-free solution. In addition,

or neuropeptides from axon termi- (which contain the subunit CaV2.2). vesicles labelled with NPY–pHluorin nals or somata. Previous studies in Moreover, short-hairpin RNA were observed (using total internal sensory neurons of the dorsal root (shRNA)-mediated knock down of reflection fluorescence (TIRF)

ganglion (DRG neurons) cultured in CaV2.2 in DRG neurons markedly microscopy) to be released upon the absence of Ca2+ have identified reduced CiVDS, further supporting depolarization in Ca2+-free or Ca2+- an alternative form of somatic vesicle a role for these channels in CiVDS. containing solution. Together, these secretion that is triggered by action To determine which functions of data suggest that ATP and NPY may 2+ potentials, known as Ca -independent the CaV2.2 channel are necessary for be released during CiVDS. but voltage-dependent secretion CiVDS, the authors introduced muta- Overall, these results characterize (CiVDS). However, the mechanisms tions in the voltage-sensing motif S4 the mechanisms underlying CiVDS. underlying CiVDS have not been clear. or in the channel-pore region and Specifically, they suggest that action Now, Zhou and colleagues characterize expressed these mutant channels in potentials are detected by the S4 the CaV2.2 the molecular mechanisms mediating DRG neurons that had been in cul- portion of the CaV2.2 channel, which synprint CiVDS and show that it results in the ture for 3 days and had spontaneously in turn signals via its synprint region site links release of ATP and neuropeptide Y reduced levels of endogenous CaV2.2 to the SNARE complex to trigger the voltage- (NPY) from DRG neurons. and impaired CiVDS compared with release of vesicles containing ATP The authors reasoned that CiVDS freshly isolated neurons. Whereas and/or NPY. The authors note that sensing probably requires a voltage sensor overexpression of wild-type or CiVDS seems to dominate over CDS function of the (likely to be found in voltage-gated pore-mutant CaV2.2 rescued CiVDS in DRG neurons at rest, and suggest channel with channels), vesicle fusion machinery in these cells, overexpression of that CiVDS may thus have a role in and a molecular means of linking S4-mutant Ca 2.2 did not, implying sensory homeostasis. the SNARE V the two. The authors tested the that the voltage-sensing function of Natasha Bray machinery to effects of various antagonists of CaV2.2 is necessary for CiVDS. ORIGINAL ARTICLE Chai, Z. et al. CaV2.2 gates enable CiVDS voltage-gated channels on CiVDS — Next, the authors hypothesized calcium-independent but voltage-dependent which can be detected as a ‘jump’ in that vesicle release during CiVDS may secretion in mammalian sensory neurons. Neuron http://dx.doi.org/10.1016/j.neuron.2017.10.028 (2017) membrane capacitance (Cm) elicited be mediated by the SNAP receptor