TRPC6 immunoreactivity is colocalized with neuronal nitric oxide synthase in extrinsic fibers innervating guinea pig intrinsic cardiac ganglia

Abstract

Tachykinins depolarize guinea pig intracardiac neurons by activating nonselective cationic channels. Recently, members of the transient receptor potential family of membrane channels (TRPC) have been implicated in the generation of G protein-coupled receptor-activated nonselective cationic currents. We have investigated whether guinea pig cardiac neurons exhibit immunoreactivity to TRPC. Our results showed that nerve fibers within guinea pig intrinsic cardiac ganglia exhibited immunoreactivity to TRPC6. After culture of cardiac ganglia whole-mount explants for 72 hours, the TRPC6-IR fiber networks were absent. Therefore, the TRPC6-IR fibers were derived from sources extrinsic to the heart. A small percentage ( approximately 3%) of intracardiac neurons also exhibited TRPC6 immunoreactivity in control preparations, and the percentage of cells exhibiting TRPC6 immunoreactivity was not changed following explant culture for 72 hours. The few intrinsic TRPC6-IR neurons also exhibited nitric oxide synthase (NOS) immunoreactivity, indicating that they were nitrergic as well. We compared the immunohistochemical staining patterns of TRPC6-IR fibers with the staining patterns of a number of other neurotransmitters or neurotransmitter synthetic enzymes that mark specific extrinsic inputs to the intrinsic cardiac ganglia. The TRPC6-IR fibers were not immunoreactive for choline acetyltransferase, tyrosine hydroxylase, or substance P. However, the TRPC6-IR fibers exhibited immunoreactivity to neuronal NOS. Therefore, we propose that the TRPC6-IR fibers within the guinea pig intrinsic cardiac ganglia are vagal sensory fibers that also contain NOS. We found, in support of this conclusion, that TRPC6-IR cells were also present in sections of nodose ganglia.

Differential expression of canonical (classical) transient receptor potential channels in guinea pig enteric nervous system

“…Preadsorption of the antibody with its immunizing peptide abolished the immunoblots (Dalrymple et al, 2002; Strübing et al, 2003; Facemire et al, 2004) and immunostaining (Calupca et al, 2002). …”

Physiological Function and Characterization of TRPCs in Neurons

“…TRPC6 is widely expressed in the cardiac neurons [92], in retinal ganglion cells [93], in the neurons of olfactory epithelium [94] and in parts of the brain, such as cortex, substantia nigra, hippocampus and cerebellum [95,96]. TRPC6 transgenic mice (that overexpress a mutant TRPC6) showed enhancement in spine formation and spatial learning and memory in Morris water maze [97,98].…”

Immunohistochemical analysis of intracardiac ganglia of the rat heart

“…Additionally, intracardiac neurons are believed to receive synaptic inputs from sympathetic and extrinsic sensory neurons (Saito et al 1986;Slavikova et al 1993Slavikova et al , 2003Onuoha et al 1999;Calupca et al 2000Calupca et al , 2002 in addition to vagal preganglionic axon inputs. Pharmacological studies suggest that transmitters such as noradrenaline, and peptides including substance P, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activated peptide (PACAP) and calcitonin-gene-related peptide (CGRP), alter the firing properties of intracardiac neurons, indicating that sensory and sympathetic neurons may also modify ganglionic transmission (Xu and Adams 1993;Cuevas and Adams 2000;Liu et al 2000;Zhang et al 2001).…”