Interactions between TRPA1 and TRPV1 in the peripheral vasculature

Aisah Aubdool1,2, Rabea Graepel1, Susan Brain1,2. 1Cardiovascular Division, King’s College London, London, SE1 9NH, United Kingdom, 2Centre for Integrative Biomedicine, King’s College London, London, SE1 9NH, United Kingdom.

Transient receptor potential (TRP) channels have multiple functions, including pain and vasoactive responses. Our group has shown that capsaicin, the classical exogenous TRPV1 agonist, stimulates an increase in mouse ear blood flow that is dependent on the release of vasodilator neuropeptides substance P and CGRP (Grant et al., 2002) and that the exogenous TRPA1 agonist mustard-oil has a similar effect (Grant et al., 2005). Recently, our group showed that mustard-oil and cinnamaldehyde cause vasodilatation in the skin of anaesthetised wildtype (WT), but not TRPA1 knockout (KO) mice (Pozsgai et al., 2010). It now appears that TRPA1 is co-expressed in approximately 50% of all TRPV1-positive sensory neurons (Andersson et al., 2008) and this evidence suggests a possible interaction between TRPA1 and TRPV1, although potential mechanisms and effects are under debate. In this study, we have investigated their possible interactions in terms of cutaneous blood flow regulation in mouse ears.

Blood flow was assessed in the ear of mice (20-30g) anaesthetised with ketamine (75mg/kg, i.p.) and medetomidine (1mg/kg, i.p.). In the first series of experiments, neurogenic vasodilatation was induced using 20µl of mustard-oil (1%) applied topically to the ipsilateral ears of either C57BL/6 TRPV1 WT or KO mice (both sexes). Blood flow was imaged using a non-invasive laser Doppler scanner (Moor Instruments, UK), allowing mean blood flow to be assessed in the whole ear. Vehicle (paraffin-oil) was applied on the contralateral ears. In a second series of experiments, female CD1 mice were pre-treated with TRPV1 antagonist SB366791 (5mg/kg, i.p.). Blood flow was measured using the laser Doppler flowmeter, which measures blood flow in a focussed restricted area (1-2mm2) of the ear. Results in each case were calculated as the area under the response curve and expressed as arbitrary flux units (×103 flux units). Results were further presented as mean ± standard error of the mean. Statistical evaluation was carried out by ANOVA + Bonferroni’s test. P values < 0.05 were considered to be statistically significant.

Mustard-oil-induced increased blood flow in both sets of experiments. This effect was significantly greater in the ears of TRPV1 KO (n = 6) compared with WT mice (n = 5); (KO 127.1 ± 13.2 (×103) units vs WT 75.8 ± 7.0 (×103) units p<0.01). Furthermore, mice pre-treated with TRPV1 antagonist SB366791 (n = 6) displayed significantly greater vasodilatation than those treated with vehicle (n = 6); (SB366791-treated 126.6 ± 21.7 (×103) units vs vehicle-treated 54.8 ± 8.2 (×103) units, p<0.001).

In conclusion, this study confirms that mustard-oil increases peripheral blood flow. Following on from our earlier findings that mustard oil-dependent vasodilatation was TRPA1- and neuropeptide-dependent, we now suggest involvement of TRPV1. TRPA1-mediated vasodilatation following mustard-oil application, was significantly potentiated by both either genetic deletion or pharmacological antagonism of TRPV1. This study indicates a potential for TRPV1 to regulate TRPA1 receptor-mediated vasodilatation in mice skin in vivo.

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Grant et al (2005). Eur. J. Pharmacol 507: 273-80.

Pozsgai et al (2010). Cardiovasc Res 87: 760-68.

Andersson et al (2008). J. Neurosci 28: 2485-89.

This study was supported by a BBSRC-led IMB capacity building award & the BHF.