Ligand- and voltage-gated Ca²⁺ channels differentially regulate the mode of vesicular neuropeptide release in mammalian sensory neurons

Neuropeptides released from dorsal root ganglion (DRG) neurons play essential roles in the neurotransmission of sensory inputs, including those underlying nociception and pathological pain. Neuropeptides are released from intracellular vesicles through two modes: a partial release mode called "kiss-and-run" (KAR) and a full release mode called "full fusion-like" (FFL). Using total internal reflection fluorescence (TIRF) microscopy, we traced the release of pH-sensitive green fluorescent protein-tagged neuropeptide Y (pHluorin-NPY) from individual dense-core vesicles in the soma and axon of single DRG neurons after Ca²⁺ influx through either voltagegated Ca²⁺ channels (VGCCs) or ligand-gated transient receptor potential vanilloid 1 (TRPV1) channels. We found that Ca²⁺ influx through VGCCs stimulated FFL and a greater single release of neuropeptides. In contrast, Ca²⁺ influx through TRPV1 channels stimulated KAR and a pulsed but prolonged release of neuropeptides that was partially mediated by Dynamin 1, which limits fusion pore expansion. Suppressing the Ca²⁺ gradient to an extent similar to that seen after TRPV1 activation abolished the VGCC preference for FFL. The findings suggest that by generating a steeper Ca²⁺ gradient, VGCCs promote a more robust fusion pore opening that facilitates FFL. Thus, KAR and FFL release modes are differentially regulated by the two principal types of Ca²⁺-permeable channels in DRG neurons.