Activation of TRPA1 by Membrane Permeable Local Anesthetics

Abstract

BackgroundLow concentrations of local anesthetics (LAs) suppress cellular excitability by inhibiting voltage-gated Na+ channels. In contrast, LAs at high concentrations can be excitatory and neurotoxic. We recently demonstrated that LA-evoked activation of sensory neurons is mediated by the capsaicin receptor TRPV1, and, to a lesser extent by the irritant receptor TRPA1. LA-induced activation and sensitization of TRPV1 involves a domain that is similar, but not identical to the vanilloid-binding domain. Additionally, activation of TRPV1 by LAs involves PLC and PI(4,5)P2-signalling. In the present study we aimed to characterize essential structural determinants for LA-evoked activation of TRPA1.ResultsRecombinant rodent and human TRPA1 were expressed in HEK293t cells and investigated by means of whole-cell patch clamp recordings. The LA lidocaine activates TRPA1 in a concentration-dependent manner. The membrane impermeable lidocaine-derivative QX-314 is inactive when applied extracellularly. Lidocaine-activated TRPA1-currents are blocked by the TRPA1-antagonist HC-030031. Lidocaine is also an inhibitor of TRPA1, an effect that is more obvious in rodent than in human TRPA1. This species-specific difference is linked to the pore region (transmembrane domain 5 and 6) as described for activation of TRPA1 by menthol. Unlike menthol-sensitivity however, lidocaine-sensitivity is not similarly determined by serine- and threonine-residues within TM5. Instead, intracellular cysteine residues known to be covalently bound by reactive TRPA1-agonists seem to mediate activation of TRPA1 by LAs.ConclusionsThe structural determinants involved in activation of TRPA1 by LAs are disparate from those involved in activation by menthol or those involved in activation of TRPV1 by LAs.

Propacetamol-Induced Injection Pain Is Associated with Activation of Transient Receptor Potential Vanilloid 1 Channels

“…Local anesthetics activate TRPV1, and lidocaine induces a strong sensitization to heat and capsaicin. The EC 50 value for lidocaine to activate rat TRPV1 was determined to be approximately 12 mM (Leffler et al, 2008), and an EC 50 value of 24 mM was subsequently found for the activation of rat TRPA1 (Leffler et al, 2011). Although TRPV2 and TRPV4 are expressed in sensory neurons, we could not detect a sensitizing or activating effect by PPCM on these channels.…”

“…Injection pain as a result of activation of TRP channels has been shown for propofol (Fischer et al, 2010), etomidate (Matta et al, 2008), and lidocaine as well as for other local anesthetics (Leffler et al, 2008(Leffler et al, , 2011. Although TRPA1 is the channel that seems to be predominantly activated by etomidate and propofol (Matta et al, 2008), the latter at least also activates TRPV1 after receptor sensitization in mouse dorsal root ganglion neurons (Fischer et al, 2010).…”

“…Many of these proalgesic substances were described to activate transient receptor potential (TRP) channels expressed in nociceptive nerve endings, and transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1 (TRPA1) currently seem to be the most relevant candidates mediating activation and/or sensitization of sensory neurons by both propofol and local anesthetics (Leffler et al, 2008(Leffler et al, , 2011Matta et al, 2008). Both TRPV1 and TRPA1 nonselective cation channels are expressed in peripheral nerve endings of nociceptive C and Ad fibers and also along the peripheral axon and in central nerve terminals in the spinal cord.…”

Apomorphine Is a Bimodal Modulator of TRPA1 Channels

“…It seems more likely that apomorphine acts as a gating modifier of TRPA1, which, at high concentrations, reduces TRPA1 single-channel open times, as can be seen from the current traces in excised inside-out patches. A similar bimodal action has been described for the modulation of TRPA1 by menthol and lidocaine (i.e., an activation at low and a block at high concentrations) (Karashima et al, 2007;Leffler et al, 2011).…”

The Molecular Basis for Species-specific Activation of Human TRPA1 Protein by Protons Involves Poorly Conserved Residues within Transmembrane Domains 5 and 6

“…It has been reported that both intracellular acidosis and alkalosis can activate rodent TRPA1 (13)(14)(15). Although the study from Wang et al (14) claims that extracellular acidosis fails to activate rodent TRPA1, a previous study suggested that extracellular protons can evoke a calcium influx through human TRPA1 expressed in HEK-293 cells (16) TRPA1 is indeed subject to a significant species specificity, and several exogenous agonists and antagonists have been shown to elicit different effects on human and rodent TRPA1 (17)(18)(19)(20)(21)(22). We therefore asked if extracellular protons interact with TRPA1 in a species-specific manner.…”