Modulation du courant Nav1.9 par l'activation des récepteurs NK3 aux neurokinines dans les neurones afférents primaires du système nerveux entérique de cochon d'inde

Dans le système nerveux entérique (SNE) de cochon d Inde, les neurones afférents primaires intrinsèques (IPANs) expriment sélectivement le canal Nav1.9 qui produit un courant Na+ résistant à la TTX, lent et persistant (INav1.9). Ils communiquent entre eux et avec les interneurones ou motoneurones par des PPSEs lents induits principalement par l activation des récepteurs NK3 (rNK3) aux neurokinines. Leur activation sensorielle déclenche des réflexes moteurs et sécréteurs. Ce travail de thèse, basé essentiellement sur l enregistrement en patch clamp d IPANs de duodenum de cobaye in situ, montre que l activation des rNK3 par l agoniste sélectif senktide, augmente INav1.9 Cet effet, transitoire du fait de la désensibilisation des rNK3, implique la PKC et résulte d un déplacement négatif de la dépendance au potentiel du canal, Il permet à INav1.9 de générer des plateaux dépolarisants et de diminuer le seuil de genèse des potentiels d action. Pour rechercher l impact fonctionnel du couplage Nav1.9/rNK3, nous avons entamé une étude comparative de la motricité du colon de souris sauvages et Nav1.9-/-. Après avoir vérifié la présence de Nav1.9 dans les neurones du colon de souris nous montrons, dans un premier temps, que la fréquence des complexes migrants myoélectriques est fortement réduite par un antagoniste des rNK3. Le couplage Nav1.9/NK3r favorise vraisemblablement la transmission synaptique dans le SNE. Ceci souligne que dans ce système, Nav1.9 et rNK3 pourraient avoir un rôle physiologique, alors qu on attribuait de rôle pour rNK3 qu en conditions extrêmes et que dans les neurones nociceptifs, Nav1.9 n agit que dans la douleur inflammatoire.In the enteric nervous system (ENS) of the guinea pig, the intrinsic primary afferent neurons (IPANs) selectively express the Nav1.9 channel, which produces a TTX-resistant, slow and persistent Na+ current (INav1.9). They communicate between themselves, and with interneurons and motoneurons by slow EPSPs that are mainly induced by neurokinin NK3 receptors (NK3r) stimulation. Their sensory activation triggers motor and secretory reflexes. This work, mainly performed by in situ IPANs patch clamp recording in the guinea pig duodenum, shows that rNK3 activation by senktide, a selective agonist, increases INav1.9. This effect, transient because of the rNK3 desensitization, involves PKC and is due to a negative shift of the voltage dependence of channel gating processes. It allows INav1.9 to generate plateau potentials and to reduce the action potential threshold. In order to examine the functional consequences of the Nav1.9/rNK3 coupling, we started a comparative study of colon motility in wild type and Nav1.9-/- mice. After having confirmed that Nav1.9 is expressed in mouse colon neurons, in a first step we show that myoelectric migrant complexe frequency is significantly reduces by a rNK3 antagonist. Nav1.9/rNK3 coupling seems to favor synaptic transmission in the ENS. It underlines that, in this system, Nav1.9 and rNK3 could play a physiological role, whereas rNK3 was though to act only in extreme conditions in gut motility and Nav1.9 is involved only in inflammatory pain in nociceptive neurons KeyAIX-MARSEILLE2-BU Méd/Odontol. (130552103) / SudocSudocFranceF

The Nav1.9 channel regulates colonic motility in mice.

International audienceThe colonic migrating motor complex (CMMC) is a major pattern of motility that is entirely generated and organized by the enteric nervous system. We have previously demonstrated that the Nav1.9 channel underlies a tetrodotoxin-resistant sodium current which modulates the excitability of enteric neurons. The aim of this study was to observe the effect of loss of the Nav1.9 channel in enteric neurons on mouse colonic motility in vitro. The mechanical activity of the circular muscle was simultaneously recorded from three sites, namely, proximal, mid- and distal, along the whole colon of male, age-matched wild-type and Nav1.9 null mice. Spontaneous CMMCs were observed in all preparations. The mean frequency of CMMCs was significantly higher in the Nav1.9 null mice (one every 2.87 ± 0.1 min compared to one every 3.96 ± 0.23 min in the wild type). The mean duration of CMMCs was shorter and the mean area-under-contraction was larger in the Nav1.9 null mice compared to the wild type. In addition, CMMCs propagated preferentially in an aboral direction in the Nav1.9 null mice. Our study demonstrates that CMMCs do occur in mice lacking the Nav1.9 channel, but their characteristics are significantly different from controls. Up to now, the Nav1.9 channel was mainly associated with nociceptive neurons and involved in their hyperexcitability after inflammation. Our result shows for the first time a role for the Nav1.9 channel in a complex colonic motor pattern

Activation of neurokinin 3 receptor increases Na(v)1.9 current in enteric neurons.

International audienceThe intrinsic primary afferent neurons (IPANs) of the guinea pig enteric nervous system express Na(v)1.9 sodium channels that produce a persistent TTX-resistant current having a low activation threshold and slow gating kinetics. These neurons receive slow EPSPs induced mainly by the activation of neurokinin 3 receptors (NK3r). Here, we demonstrate that senktide, a specific NK3r agonist, potentiates the Na(v)1.9 current (I(Nav1.9)) in IPANs. Using whole-cell patch-clamp recordings from IPANs in duodenum longitudinal muscle/myenteric plexus preparations, we show that short (1-5 s) and long (up to 1 min) applications of senktide, increase the I(Nav1.9) peak current up to 13-fold. The effect, blocked by a NK3r antagonist SB235375 is transient, lasting approximately 2 min and is due to a negative shift of the activation voltage by approximately 20 mV and of fast inactivation by approximately 10 mV. As a consequence, the window current resulting from the product of the activation and fast inactivation curves is shifted and enlarged. The transient effect of senktide is likely to be due to the fast desensitization of NK3r. Protein kinase C (PKC) activation with phorbol or oleoyl acetylglycerol also increases I(Nav1.9), although persistently, by inducing similar voltage-dependent changes. Current-clamp experiments showed that I(Nav1.9) modulation by senktide lowers action potential threshold and increases excitability. The increase in I(Nav1.9) by NK3r activation is also likely to amplify slow EPSPs generated in the IPANs. These changes in excitability potentially have a profound effect on the entire enteric synaptic circuit and ultimately on gut motility and secretion