T1667 Canonical Transient Receptor Potential Channels (TRPC Channels) in Regulation of Mucosal Chloride Secretion in Guinea Pig Ileum

Abstract

G A A b st ra ct s and involved in the various gut function. However little is known about the subpopulations of TRPV1-expressing nerves and sensory peptidergic nerves in gut. We previously demonstrated that TRPV1-positive nerve fibers in rectum were most abundant among the regions of mouse large intestine. In the present study, we investigated the immunohistochemical distribution of TRPV1 channels and sensory neuropeptides and their co-localization in mouse rectum. METHODS: Extensive TRPV1-immunoreactivity was detected by using immunohistochemical staining with fluorescein-conjugated tyramide amplification. Protein gene product 9.5 (PGP), CGRP, substance P (SP) and neurokinin A (NKA)-immunoreactivity was also detected by indirect staining with their specific antibodies. The longitudinal change in smooth muscle tone was isotonically measured using Magnus apparatus. RESULTS: The localization of TRPV1 was studied at both transverse and horizontal planes of sections in mouse rectum. Numerous TRPV1-immunoreactive nerve fibers were clearly detected in the mucosal, submucosal layer and myenteric plexus. In contrast, TRPV1 nerve fibers were sparsely distributed in circular and longitudinal muscle layers. Next, double labeling studies were carried out. In the mucosal layer, all the TRPV1 nerve fibers were found to colocalize with PGP and CGRP. SP and NKA positive nerve fibers were not observed. TRPV1 nerve fibers containing both CGRP and SP were observed running around blood vessels in the submucosal layer. In the myenteric plexus, most of the TRPV1 axons were found to colocalize with PGP and CGRP. Relatively small numbers of TRPV1 axons were immunopositive for SP. NKA and SP-immunoreactive axons were observed in the circular and longitudinal muscle, and the cell bodies were detected in the myenteric plexus. NKA and SP were almost colocalized at the axons and cell bodies in muscle layer. In the Magnus experiment, capsaicininduced contraction was significantly inhibited by NK1 and NK2 receptor antagonists. DISCUSION: The present results suggest that TRPV1 nerve fibers in mouse rectum are extrinsic primary afferents. TRPV1 fibers containing CGRP are distributed in mucosal, submucosal layer and myenteric plexus and play various roles in rectal function. TRPV1 fibers containing SP and/or NKA are distributed in myenteric plexus and involved in rectal motor function by stimulating intrinsic excitatory motor neurons.