Table 1.
Ionotropic receptors and ligand-gated ion channels expressed by nociceptive primary afferent neurons
| Receptor/Channel | Major subtypes | Ligand | Expression (cell size/type) | Notes | Function |
|---|---|---|---|---|---|
| Purine | P2X2 P2X3 | ATP, ADP, Adenosine | P2X3, IB4 positive cells | P2X2 modulated by protons; P2X3 GDNF regulated | IMR, SyMR, AR |
| Acid-sensing proton-gated | DRASIC, ASIC (α, β) | Protons | DRASIC, Small. ASICs α, Small β, Small/large | Amiloride sensitive; Mechanosensitive? | ST, IMR, SyMR |
| Vanilloid | VR1 | Heat, capsaicin | Small | Sensitized by heat; Proton-gated; NGF-regulated | ST, IMR |
| Sodium TTXr | SNS/PN3 SNS2/NaN | N/A | Small | PKA and PKC substrate; NGF regulated | EMC |
| Sodium TTXs | PN1, PN4, rB(I-III) | N/A | All cells | NGF regulated | EMC |
| Calcium voltage-gated channels | T- (low-threshold) L-, N- (highthreshold) | N/A | T, Small/medium L, N, Mainly small | Secondary calcium currents mediated by G protein-coupled receptors, e.g. bradykinin; Enhancement of high threshold current by PKC | SyMC |
| Serotonin | 5HT-3 | Serotonin | Small | IMR, ST | |
| NMDA | NR1 NRgbs | Glutamate/aspartate | Small/large | Controls SP release | SyMR, AR |
| AMPA | iGluR1-3 | Glutamate | R1, Small | SyMR, AR | |
| R2–3, Small/large | |||||
| Kainate | iGluR5 | Glutamate | Small | Controls neurotransmitter release | SyMR, AR |
IMR, inflammatory mediator receptor; SyMR, synaptic modulator receptor; SyMC, synaptic modulator channel; ST, signal transducer; EMC, excitatory modulator channel; AR, autoreceptor; N/A, not applicable.