Substance P mobilizes intracellular calcium and activates a nonselective cation conductance in rat spiral ganglion neurons

Abstract

We demonstrate the expression of functional tachykinin receptors in rat spiral ganglion neurons (SGNs) using calcium signal measurement and whole-cell patch clamp recording. Substance P (SP; 10 microm, 1 s application) induced a transient increase in intracellular calcium. The SP dose-response study showed an EC50 of 18.8 microm and a Hill slope of 0.77. Comparison between specific agonists for the three tachykinin receptor (NKR) types showed the potency NKR3 > NKR1 > NKR2 at 10 microm. The Ca2+ response could be evoked in Ca2+-free medium and was blocked by N-ethylmaleimide and U-73122, indicating that Ca2+ was released from intracellular stores via a G-protein and phospholipase C pathway. Under whole-cell voltage clamp recording at a holding potential of -50 mV, SP (10 microm, 1 s) evoked a slowly developing transient inward current. The current reversed near to 0 mV and ionic permeability experiments revealed a cation nonselective conductance also permeable to large organic cations such as N-methyl-D-glucamine and tetraethylammonium. Neither removing extracellular calcium nor chelating intracellular calcium with 10 mm BAPTA could block the SP-evoked current. This conductance appeared coupled to G-protein activation as intracellular GDP-betaS blocked the SP-evoked current. Mutual desensitization and occlusion studies with acetylcholine and ATP showed that the SP-evoked conductance share effector channels and/or intracellular processes with the purinergic/cholinergic conductance. In SGNs, SP could have both a trophic action, via a calcium response, and a neuromodulatory role, by a depolarizing action through the activation of nonselective cation channels.

Purinergic signaling in cochleovestibular hair cells and afferent neurons

“…10 of [33] and Fig. 5 of [34].) By these experiments, the P2Y receptor (P2YR)-mediated conductance was demonstrated to share the final effector channel with mAChR and NKR.…”

Differential expression of P2Y receptors in the rat cochlea during development

“…The SGN P2X receptors exhibit desensitizing currents in response to micromolar ATP [59][60][61], while the P2Y receptors are activated by nanomolar ATP and UTP concentrations, and via intracellular second messenger signaling, engage a slowly developing non-selective cation conductance [62]. The identity of this cation conductance is thought to be a TRP channel which provides cross-talk with other metabotropic receptors involving the GPCR-PLC -DAG pathway, including the muscarinic acetylcholine receptor and the substance P receptor [17,63]. Given the high level of TRPC3 recently identified in guinea pig and mouse SGN somata [57,64], this channel is the most likely candidate, akin to the situation in the outer hair cells.…”

NMDA Channels Together With L-Type Calcium Currents and Calcium-Activated Nonspecific Cationic Currents Are Sufficient to Generate Windup in WDR Neurons

“…The effects of the activation of NK1 receptors are not totally clear but they seem to include both a membrane conductance change and an increase in intracellular calcium concentration, which probably results from the release of calcium from intracellular buffers (Ito et al 2002). Our NK1 model included these two major mechanisms, the slow conductance change generating a slow depolarizing nonspecific cat- FIG. 2.…”