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

Authors

  • Ken Ito,

    1. Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, INSERM EMI 99–27, Université de Bordeaux 2, Hôpital Pellegrin Bat PQR, Bordeaux, France
    2. Department of Otolaryngology, Faculty of Medicine, University of Tokyo, Tokyo, Japan
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  • Claire Rome,

    1. Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, INSERM EMI 99–27, Université de Bordeaux 2, Hôpital Pellegrin Bat PQR, Bordeaux, France
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  • Yohan Bouleau,

    1. Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, INSERM EMI 99–27, Université de Bordeaux 2, Hôpital Pellegrin Bat PQR, Bordeaux, France
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  • Didier Dulon

    1. Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, INSERM EMI 99–27, Université de Bordeaux 2, Hôpital Pellegrin Bat PQR, Bordeaux, France
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: Dr D. Dulon, as above.
E-mail: didier.dulon@bordeaux.inserm.fr

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 µm, 1 s application) induced a transient increase in intracellular calcium. The SP dose–response study showed an EC50 of 18.8 µm 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 µm. 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 µm, 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-βS 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.

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