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Low voltage‐activated calcium channels gate transmitter release at the dorsal root ganglion sandwich synapse
Author(s) -
Rozanski Gabriela M.,
Nath Arup R.,
Adams Michael E.,
Stanley Elise F.
Publication year - 2013
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2013.260281
Subject(s) - dorsal root ganglion , neurotransmission , synapse , neuroscience , neuron , depolarization , voltage dependent calcium channel , biophysics , chemistry , calcium , biology , sensory system , biochemistry , receptor , organic chemistry
Key points• Sensory neurons in dorsal root ganglia (DRG) lack direct inter‐somatic synaptic contacts but a subpopulation can communicate with their immediate neighbours via transglial, neuron–glial cell–neuron ‘sandwich synapses’. • We used gently dissociated chick DRG to explore the properties and identity of the voltage sensitive calcium channel responsible for gating transmitter (ATP) release at the neuron‐to‐glial cell synapse. • A combined pharmacological and biophysical characterization identified the T type, CaV3.2 calcium channel. • The low voltage‐activated and inactivation‐sensitive properties of CaV3.2 suggest that sandwich synapse transmission is gated not only by action potentials but also by sub‐threshold membrane depolarizations. • CaV3.2 modulating agents are of interest as anaesthetics, raising the possibility that sandwich synapse transmission plays a role in the aetiology of DRG‐derived abnormal sensation and pain.Abstract A subpopulation of dorsal root ganglion (DRG) neurons are intimately attached in pairs and separated solely by thin satellite glial cell membrane septa. Stimulation of one neuron leads to transglial activation of its pair by a bi‐, purinergic/glutamatergic synaptic pathway, a transmission mechanism that we term sandwich synapse (SS) transmission. Release of ATP from the stimulated neuron can be attributed to a classical mechanism involving Ca 2+ entry via voltage‐gated calcium channels (CaV) but via an unknown channel type. Specific blockers and toxins ruled out CaV1, 2.1 and 2.2. Transmission was, however, blocked by a moderate depolarization (−50 mV) or low‐concentration Ni 2+ (0.1 m m ). Transmission persisted using a voltage pulse to −40 mV from a holding potential of −80 mV, confirming the involvement of a low voltage‐activated channel type and limiting the candidate channel type to either CaV3.2 or a subpopulation of inactivation‐ and Ni 2+ ‐sensitive CaV2.3 channels. Resistance of the neuron calcium current and SS transmission to SNX482 argue against the latter. Hence, we conclude that inter‐somatic transmission at the DRG SS is gated by CaV3.2 type calcium channels. The use of CaV3 family channels to gate transmission has important implications for the biological function of the DRG SS as information transfer would be predicted to occur not only in response to action potentials but also to sub‐threshold membrane voltage oscillations. Thus, the SS synapse may serve as a homeostatic signalling mechanism between select neurons in the DRG and could play a role in abnormal sensation such as neuropathic pain.