Abstract
Background and purpose. Arachidonic acid (AA) and its derivatives are important modulators of cellular signalling. The transient receptor potential cation channel subfamily A, member 1 (TRPA1) is a cation channel with important functions in mediating cellular responses to noxious stimuli and inflammation. There is limited information about the interactions between AA itself and TRPA1, so we investigated the effects of AA and key ethanolamide and amino acid/neurotransmitter derivatives of AA on hTRPA1.Experimental approach. HEK 293 cells expressing hTRPA1 were studied by measuring changes in intracellular calcium ([Ca]i) with a fluorescent dye and by standard whole cell patch clamp recordings.Key results. AA (30 μM) increased fluorescence in hTRPA1 expressing cells by 370% (notional EC50 13 μM). The covalent TRPA1 agonist cinnamaldehyde (300 μM) increased fluorescence by 430% (EC50, 11 μM). Anandamide (230%) and N-arachidonoyl tyrosine (170%) substantially activated hTRPA1 at 30 μM, however, N-arachidonoyl conjugates of glycine and taurine were less effective while N-acyl conjugates of 5-HT did not affect hTRPA1. Changing the acyl chain length or the number and position of double bonds reduced fatty acid efficacy at hTRPA1. Mutant hTRPA1 (Cys621, Cys641 and Cys665 changed to Ser) could be activated by AA (100 μM, 40% of wild type) but not by cinnamaldehyde (300 μM).Conclusions and implications. AA is a more potent activator of TRPA1 than its ethanolamide or amino acid/neurotransmitter derivatives and acts via a mechanism distinct from that of cinnamaldehyde, further underscoring the likelyhood of multiple pharmacologically exploitable sites on hTRPA1.
Highlights
The transient receptor potential ankyrin 1 channel (TRPA1; Alexander, Mathie & Peters, 2011, Story et al, 2003) is expressed on primary afferent nociceptors where it detects potentially damaging environmental stimuli such as noxious cold, changes in pH, noxious chemicals and endogenous products of inflammation
In this study we have examined the activation of recombinant human TRPA1 by arachidonic acid and other long chain fatty acids as well as by N -arachidonoyl neurotransmitter/amino acid conjugates (NAAN), a large family of endogenous modulators of ion channels and G protein coupled receptors (Connor, Vaughan & Vandenberg, 2010)
The principle finding of our study is that Arachidonic acid (AA) and NAANs activate human TRPA1, NAAN do so less effectively than AA
Summary
The transient receptor potential ankyrin 1 channel (TRPA1; Alexander, Mathie & Peters, 2011, Story et al, 2003) is expressed on primary afferent nociceptors where it detects potentially damaging environmental stimuli such as noxious cold, changes in pH, noxious chemicals and endogenous products of inflammation. A mutagenesis study by (Liu et al, 2010) showed that reactive and non-reactive compounds such as NPPB saw their peak [Cai] response reduced for single cysteine mutations to a serine. Xiao described that these residues are important for the activation of the channel mediated by menthol, another non-reactive compound (Xiao et al, 2008). AA is a more potent activator of TRPA1 than its ethanolamide or amino acid/neurotransmitter derivatives and acts via a mechanism distinct from that of cinnamaldehyde, further underscoring the likelyhood of multiple pharmacologically exploitable sites on hTRPA1
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