title: 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.
authors.affiliation: Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, INSERM EMI 99-27, Université de Bordeaux 2, Hôpital Pellegrin Bat PQR, Bordeaux, France.
authors.forename: Ken
authors.initials: K
authors.lastname: Ito
authors.forename: Claire
authors.initials: C
authors.lastname: Rome
authors.forename: Yohan
authors.initials: Y
authors.lastname: Bouleau
authors.forename: Didier
authors.initials: D
authors.lastname: Dulon
mesh_terms: D000109:Acetylcholine / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D027682:Cation Transport Proteins / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D013136:Spiral Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013373:Substance P / Q000378:metabolism* / Q000494:pharmacology; D010738:Type C Phospholipases / Q000187:drug effects / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D002614:Chelating Agents; D004791:Enzyme Inhibitors; D011500:Protein Synthesis Inhibitors; D013373:Substance P; D000255:Adenosine Triphosphate; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D000109:Acetylcholine; D002118:Calcium