title: Permeation and block of TRPV1 channels by the cationic lidocaine derivative QX-314.
abstract: QX-314 (N-ethyl-lidocaine) is a cationic lidocaine derivative that blocks voltage-dependent sodium channels when applied internally to axons or neuronal cell bodies. Coapplication of external QX-314 with the transient receptor potential vanilloid 1 protein (TRPV1) agonist capsaicin produces long-lasting sodium channel inhibition in TRPV1-expressing neurons, suggestive of QX-314 entry into the neurons. We asked whether QX-314 entry occurs directly through TRPV1 channels or through a different pathway (e.g., pannexin channels) activated downstream of TRPV1 and whether QX-314 entry requires the phenomenon of "pore dilation" previously reported for TRPV1. With external solutions containing 10 or 20 mM QX-314 as the only cation, inward currents were activated by stimulation of both heterologously expressed and native TRPV1 channels in rat dorsal root ganglion neurons. QX-314-mediated inward current did not require pore dilation, as it activated within several seconds and in parallel with Cs-mediated outward current, with a reversal potential consistent with PQX-314/PCs = 0.12. QX-314-mediated current was no different when TRPV1 channels were expressed in C6 glioma cells, which lack expression of pannexin channels. Rapid addition of QX-314 to physiological external solutions produced instant partial inhibition of inward currents carried by sodium ions, suggesting that QX-314 is a permeant blocker. Maintained coapplication of QX-314 with capsaicin produced slowly developing reduction of outward currents carried by internal Cs, consistent with intracellular accumulation of QX-314 to concentrations of 50-100 μM. We conclude that QX-314 is directly permeant in the "standard" pore formed by TRPV1 channels and does not require either pore dilation or activation of additional downstream channels for entry.
authors.affiliation: Dept. of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Michelino
authors.initials: M
authors.lastname: Puopolo
authors.forename: Alexander M
authors.initials: AM
authors.lastname: Binshtok
authors.forename: Gui-Lan
authors.initials: GL
authors.lastname: Yao
authors.forename: Seog Bae
authors.initials: SB
authors.lastname: Oh
authors.forename: Clifford J
authors.initials: CJ
authors.lastname: Woolf
authors.forename: Bruce P
authors.initials: BP
authors.lastname: Bean
mesh_terms: D000200:Action Potentials; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D045744:Cell Line, Tumor; D002586:Cesium / Q000494:pharmacology; D017630:Connexins / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology; D006801:Humans; D017136:Ion Transport / Q000187:drug effects*; D008012:Lidocaine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D017630:Connexins; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; D002586:Cesium; C012647:QX-314; D008012:Lidocaine; D012964:Sodium; D002211:Capsaicin