RT Journal Article
SR Electronic
T1 Requirement of a Soluble Intracellular Factor for Activation of Transient Receptor Potential A1 by Pungent Chemicals: Role of Inorganic Polyphosphates
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 6500
OP 6509
DO 10.1523/JNEUROSCI.0623-07.2007
VO 27
IS 24
A1 Donghee Kim
A1 Eric J. Cavanaugh
YR 2007
UL http://www.jneurosci.org/content/27/24/6500.abstract
AB Pungent chemicals such as allyl isothiocyanate (AITC), cinnamaldehyde, and allicin, produce nociceptive sensation by directly activating transient receptor potential A1 (TRPA1) expressed in sensory afferent neurons. In this study, we found that pungent chemicals added to the pipette or bath solution easily activated TRPA1 in cell-attached patches but failed to do so in inside-out or outside-out patches. Thus, a soluble cytosolic factor was required to activate TRPA1. N-Ethylmaleimide, (2-aminoethyl)-methane thiosulfonate, 2-aminoethoxydiphneyl borate, and trinitrophenol, compounds that are known to activate TRPA1, also failed to activate it in inside-out patches. To identify a factor that supports activation of TRPA1 by pungent chemicals, we screened ∼30 intracellular molecules known to modulate ion channels. Among them, pyrophosphate (PPi) and polytriphosphate (PPPi) were found to support activation of TRPA1 by pungent chemicals. Structure–function studies showed that inorganic polyphosphates (polyPn, where n = number of phosphates) with at least four phosphate groups were highly effective (polyP4 ≈ polyP65 ≈ polyP45 ≈ polyP25 > PPPi > PPi), with K1/2 values ranging from 0.2 to 2.8 mm. Inositol-trisphosphate and inositol-hexaphosphate also partially supported activation of TRPA1 by AITC. ATP, GTP, and phosphatidylinositol-4,5-bisphosphate that have three phosphate groups did not support TRPA1 activation. TRPA1 recorded from cell bodies of trigeminal ganglion neurons showed similar behavior with respect to sensitivity to pungent chemicals; no activation was observed in inside-out patches unless a polyphosphate was present. These results show that TRPA1 requires an intracellular factor to adopt a functional conformation that is sensitive to pungent chemicals and suggest that polyphosphates may partly act as such a factor.