title: The molecular basis for species-specific activation of human TRPA1 protein by protons involves poorly conserved residues within transmembrane domains 5 and 6.
abstract: The surveillance of acid-base homeostasis is concerted by diverse mechanisms, including an activation of sensory afferents. Proton-evoked activation of rodent sensory neurons is mainly mediated by the capsaicin receptor TRPV1 and acid-sensing ion channels. In this study, we demonstrate that extracellular acidosis activates and sensitizes the human irritant receptor TRPA1 (hTRPA1). Proton-evoked membrane currents and calcium influx through hTRPA1 occurred at physiological acidic pH values, were concentration-dependent, and were blocked by the selective TRPA1 antagonist HC030031. Both rodent and rhesus monkey TRPA1 failed to respond to extracellular acidosis, and protons even inhibited rodent TRPA1. Accordingly, mouse dorsal root ganglion neurons lacking TRPV1 only responded to protons when hTRPA1 was expressed heterologously. This species-specific activation of hTRPA1 by protons was reversed in both mouse and rhesus monkey TRPA1 by exchange of distinct residues within transmembrane domains 5 and 6. Furthermore, protons seem to interact with an extracellular interaction site to gate TRPA1 and not via a modification of intracellular N-terminal cysteines known as important interaction sites for electrophilic TRPA1 agonists. Our data suggest that hTRPA1 acts as a sensor for extracellular acidosis in human sensory neurons and should thus be taken into account as a yet unrecognized transduction molecule for proton-evoked pain and inflammation. The species specificity of this property is unique among known endogenous TRPA1 agonists, possibly indicating that evolutionary pressure enforced TRPA1 to inherit the role as an acid sensor in human sensory neurons.
authors.affiliation: Department of Anesthesia and Critical Care Medicine, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany. delaroche.jeanne@mh-hannover.de
authors.forename: Jeanne
authors.initials: J
authors.lastname: de la Roche
authors.forename: Mirjam J
authors.initials: MJ
authors.lastname: Eberhardt
authors.forename: Alexandra B
authors.initials: AB
authors.lastname: Klinger
authors.forename: Nancy
authors.initials: N
authors.lastname: Stanslowsky
authors.forename: Florian
authors.initials: F
authors.lastname: Wegner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Koppert
authors.forename: Peter W
authors.initials: PW
authors.lastname: Reeh
authors.forename: Angelika
authors.initials: A
authors.lastname: Lampert
authors.forename: Michael J M
authors.initials: MJ
authors.lastname: Fischer
authors.forename: Andreas
authors.initials: A
authors.lastname: Leffler
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002211:Capsaicin / Q000494:pharmacology; D002478:Cells, Cultured; D000081007:Cymenes; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin / Q000494:pharmacology; D008253:Macaca mulatta; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D039821:Monoterpenes / Q000494:pharmacology; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D011522:Protons; D051381:Rats; D013045:Species Specificity; D000074025:TRPA1 Cation Channel; D050051:Transient Receptor Potential Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D000081007:Cymenes; D039821:Monoterpenes; D009419:Nerve Tissue Proteins; D011522:Protons; D000074025:TRPA1 Cation Channel; C473350:TRPA1 protein, human; D050051:Transient Receptor Potential Channels; D015759:Ionomycin; C073316:carvacrol; D011188:Potassium; D002211:Capsaicin; D002118:Calcium
keywords: Acid-sensing Ion Channels (ASIC); Acidosis; Nociceptor; Pain; Patch Clamp; Species Specificity; TRP Channels