TRPA1 expression and its functional activation in rodent cortex.

Ehsan Kheradpezhouh,Vincent R Daria,Julian M C Choy,Ehsan Arabzadeh

doi:10.1098/rsob.160314

Abstract

TRPA1 is a non-selective cation channel involved in pain sensation and neurogenic inflammation. Although TRPA1 is well established in a number of organs including the nervous system, its presence and function in the mammalian cortex remains unclear. Here, we demonstrate the expression of TRPA1 in rodent somatosensory cortex through immunostaining and investigate its functional activation by whole-cell electrophysiology, Ca2+ imaging and two-photon photoswitching. Application of TRPA1 agonist (AITC) and antagonist (HC-030031) produced significant modulation of activity in layer 5 (L5) pyramidal neurons in both rats and mice; AITC increased intracellular Ca2+ concentrations and depolarized neurons, and both effects were blocked by HC-030031. These modulations were absent in the TRPA1 knockout mice. Next, we used optovin, a reversible photoactive molecule, to activate TRPA1 in individual L5 neurons of rat cortex. Optical control of activity was established by applying a tightly focused femtosecond-pulsed laser to optovin-loaded neurons. Light application depolarized neurons (n = 17) with the maximal effect observed at λ = 720 nm. Involvement of TRPA1 was further confirmed by repeating the experiment in the presence of HC-030031, which diminished the light modulation. These results demonstrate the presence of TRPA1 in L5 pyramidal neurons and introduce a highly specific approach to further understand its functional significance.

Highlights

Transient receptor potential ankyrin 1 (TRPA1) is a member of the ancient superfamily of transient receptor potential (TRP) channels that are generally involved in pain, thermal and chemical sensation [1,2]
We investigated the expression of TRPA1 in the rat somatosensory cortex
We used optovin photoswitching for selective targeting of TRPA1 channels that were endogenous to the cortical neurons

Summary

Introduction

Transient receptor potential ankyrin 1 (TRPA1) is a member of the ancient superfamily of transient receptor potential (TRP) channels that are generally involved in pain, thermal and chemical sensation [1,2]. The N-terminal contains 14–18 ankyrin repeat domains which represent the binding site for TRPA1 activators including non-specific irritants and Ca2þ [1,3,4,5,6]. TRPA1 is broadly expressed throughout the body including brain, heart, small intestine, lung, bladder, joints and skeletal muscles [7,8,9,10,11,12,13,14,15]. TRPA1 is prominently present in the nociceptive neurons of dorsal root ganglia (DRG) and the trigeminal ganglia [19], and is activated by a range of irritants including mustard oil, acrolein, formalin and 4-hydroxynonenal [1,3,20,21,22]. In the central nervous system, TRPA1 is studied in the hippocampus [14] and the supraoptic nucleus of the brain stem [7,23]

Methods

Results

Conclusion