The Quaternary Lidocaine Derivative, QX-314, Exerts Biphasic Effects on Transient Receptor Potential Vanilloid Subtype 1 Channels In Vitro 

Abstract

Background: Transient receptor potential vanilloid subfamily member 1 (TRPV1) channels are important integrators of noxious stimuli with pronounced expression in nociceptive neurons. The experimental local anesthetic, QX-314, a quaternary (i.e., permanently charged) lidocaine derivative, recently has been shown to interact with and permeate these channels to produce nociceptive and sensory blockade in animals in vivo. However, little is known about the specific interactions between QX-314 and TRPV1 channels. Thus, the authors examined the mechanistic basis by which QX-314 acts on TRPV1 channels. Methods: The authors conducted an in vitro laboratory study in which they expressed TRPV1 and TRPV4 channels in Xenopus laevis oocytes and recorded cation currents with the two-electrode voltage clamp method. They used confocal microscopy for Ca 2ϩ imaging in TRPV1 transient transfected tsA201 cells. Drugs were bath-applied by gravity perfusion. Statistical analyses were performed using Student t test, ANOVA, and post tests as appropriate (P Ͻ 0.05).

Extracellular Quaternary Ammonium Blockade of Transient Receptor Potential Vanilloid Subtype 1 Channels Expressed in Xenopus laevis Oocytes

“…These findings are in good agreement with an earlier observation that capsaicin-evoked TRPV1 inward currents can be inhibited by extracellular lidocaine in mammalian human embryonic kidney 293t cells, although with significantly lower potency (Leffler et al, 2008). Furthermore, we have recently shown that the extracellular administration of the quaternary lidocaine derivative, QX-314, inhibits TRPV1-mediated currents in X. laevis oocytes (Rivera-Acevedo et al, 2011). Taken together, these results suggest that it is a general trait of titratable LAs to inhibit TRPV1-mediated inward currents.…”

“…We previously showed that the quaternary lidocaine derivative, QX-314, inhibits capsaicin-activated TRPV1 channels (Rivera-Acevedo et al, 2011). Benzocaine, on the other hand, which features a lipophilic aromatic moiety that is shared with both lidocaine and QX-314 but lacks a nitrogen that can be charged under physiological conditions, did not inhibit TRPV1 currents (see above).…”

“…For example, application of the TRPV1 agonist, capsaicin, has been shown to allow transmembrane passage of the permanently charged lidocaine derivative, N-(2,6-dimethylphenylcarbamoylmethyl)triethylammonium (QX-314), presumably via the "dilated" TRPV1 permeation pathway (Binshtok et al, 2007;Chung et al, 2008;Ries et al, 2009). Subsequently, lidocaine and also QX-314 were demonstrated to directly interact with TRPV1 channels in various preparations, exhibiting both activating and inhibiting properties (Leffler et al, 2008;Rivera-Acevedo et al, 2011). In Xenopus laevis oocytes, we have found that lidocaine and QX-314 exert biphasic effects on TRPV1 channels, inhibiting capsaicin-evoked TRPV1 currents at lower (micromolar) concentrations and activating TRPV1 channels at higher (millimolar) concentrations.…”

Expression-dependent pharmacology of transient receptor potential vanilloid subtype 1 channels inXenopus laevisoocytes

“…We have previously shown that TRPV1 channels, expressed in Xenopus leavis oocytes, are reversibly inhibited by the quaternary ammonium compound QX-314 with micromolar affinity. 16 In contrast, our follow-up study demonstrated that the amplitudes (from 100 nA to 15 μA), which we assumed to roughly correlate with channel expression levels. In single drug application experiments, 1 or 10 μM QX-314 were co-applied with an approximate EC 50 concentration of capsaicin (15 μM) to oocytes expressing varying levels of TRPV1 channels.…”

“…One obvious candidate is the pore domain, with its selectivity filter being the final integrator of the diverse stimuli acting on the ion channel, ultimately biasing the open-closed equilibrium. To this end, we and others have demonstrated extracellular TRPV1 inhibition by charged or chargeable ammonium compounds, 16,17 and we have recently shown that these compounds likely target the channel pore.…”