The Nav1.9 channel regulates colonic motility in mice

Abstract

The 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.

Keywords: Nav1.9 channel; colon; enteric; migrating motor complex; neuron.

Figure 1

Localization of Na_v1.9 immunoreactivity in the myenteric plexus of the mouse colon. Na_v1.9-like immunoreactivity, detected with L-23 AB (A), is located in large neurons (arrowheads) that are NF-200 positive (B) and in smaller NF-200 negative neurons. These two neuron populations are well evidenced on the overlay (C). Scale bar = 50 μm.

Figure 2

Mechanical recordings made simultaneously from three sites of the colon. (A) and (B) are typical traces of migrating motor complexes in the colon (CMMCs) of wild (+/+) and Na_v1.9^−/− mice, respectively. In Na_v1.9^−/− mice, the interval between CMMCs and their duration were shorter and the area higher than in wild-type mice.

Figure 3

Graphic representation of the period of CMMCs in the proximal, mid- and distal colon of wild-type and Na_v1.9^−/− mice. The period of CMMC in Na_v1.9^−/− mice was found to be significantly shorter than in +/+ mice. ^aP < 0.05, ^bP < 0.01 vs. +/+ mice.

Figure 4

Graphic representation of the duration of CMMCs in the proximal, mid- and distal colon of wild-type and Na_v1.9^−/− mice. The duration of CMMCs in Na_v1.9^−/− mice was found to be significantly shorter than in +/+ mice. ^aP < 0.05, ^bP < 0.01 vs. +/+ mice.

Figure 5

Graphic representation of the area of CMMCs in the proximal, mid- and distal colon of wild-type and Na_v1.9^−/− mice. The area of CMMCs in Na_v1.9^−/− mice was found to be significantly larger than in +/+ mice. In Na_v1.9^−/− mice, the area of CMMCs in the proximal colon was significantly smaller than in the distal region. ^aP < 0.05, ^bP < 0.01 vs. +/+ mice; ^cP < 0.01 proximal vs. distal colon in Na_v1.9^−/− mice.

Figure 6

Graphic representation of the site of origin of CMMCs in wild-type and Na_v1.9^−/− mice. In +/+ mice, about 50% of CMMCs propagated from the proximal region. This proportion increased to 75% in Na_v1.9^−/− mice. The site of origin of CMMCs was significantly different in the colon of Na_v1.9^−/− mice compared to that of +/+ mice (P < 0.05).