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Background and Purpose Selective nociceptor fibre block is achieved by introducing the cell membrane impermeant sodium channel blocker lidocaine N-ethyl bromide ( QX-314) through transient receptor potential V1 ( TRPV1) channels into nociceptors. We screened local anaesthetics for their capacity to activate TRP channels, and characterized the nerve block obtained by combination with QX-314. Experimental Approach We investigated TRP channel activation in dorsal root ganglion ( DRG) neurons by calcium imaging and patch-clamp recordings, and cellular QX-314 uptake by MS. To characterize nerve block, compound action potential ( CAP) recordings from isolated nerves and behavioural responses were analysed. Key Results Of the 12 compounds tested, bupivacaine was the most potent activator of ruthenium red-sensitive calcium entry in DRG neurons and activated heterologously expressed TRPA1 channels. QX-314 permeated through TRPA1 channels and accumulated intracellularly after activation of these channels. Upon sciatic injections, QX-314 markedly prolonged bupivacaine's nociceptive block and also extended (to a lesser degree) its motor block. Bupivacaine's blockade of C-, but not A-fibre, CAPs in sciatic nerves was extended by co-application of QX-314. Surprisingly, however, this action was the same in wild-type, TRPA1-knockout and TRPV1/ TRPA1-double knockout mice, suggesting a TRP-channel independent entry pathway. Consistent with this, high doses of bupivacaine promoted a non-selective, cellular uptake of QX-314. Conclusions and Implications Bupivacaine, combined with QX-314, produced a long-lasting sensory nerve block. This did not require QX-314 permeation through TRPA1, although bupivacaine activated these channels. Regardless of entry pathway, the greatly extended duration of block produced by QX-314 and bupivacaine may be clinically useful. [ABSTRACT FROM AUTHOR]

Background Two transient receptor potential ( TRP) channels, TRPV1 and TRPA1, have been physiologically studied with regard to noxious heat transduction. Evidence argues against these channels as sole transducers of noxious heat or cold, respectively. Moreover, in submammalian species the TRPA1 orthologue shows heat sensitivity. Methods In vitro, single-fibre and compound action potential recordings from C-fibres as well as measurements of stimulated cutaneous CGRP release are combined with behavioural experiments to assess heat responsiveness in wild type mice, TRPA1 and TRPV1 as well as double-null mutants. Results Heat thresholds of cutaneous C-mechano-heat sensitive fibres were significantly higher in TRPA1−/− (43 ° C) than +/+ (40 ° C) mice, and averaged heat responses were clearly weaker, whereas TRPV1−/− showed normal heat thresholds and responses (up to 46 ° C). Compound action potential recordings revealed much less activity-dependent slowing of conduction velocity upon noxious heat stimulation in TRPA1−/− and a delayed deficit in TRPV1−/− in comparison to controls. Heat-induced calcitonin gene-related peptide release was reduced in TRPV1−/− but not TRPA1−/− animals. Paw withdrawal latencies to radiant heat were significantly elevated in TRPA1−/−, more so in TRPV1−/− animals. In general, double-null mutants were similar to TRPV1−/− except for the single-fibre heat responses which appeared as weak as in TRPA1−/−. Conclusions Our results indicate that in addition to TRPV1, TRPA1 plays a role in heat nociception, in particular in definition of the heat threshold, and might therefore serve as a therapeutic target in acute inflammatory pain. [ABSTRACT FROM AUTHOR]