TRPA1 and TRPV1 are required for lidocaine-evoked calcium influx and neuropeptide release but not cytotoxicity in mouse sensory neurons

BACKGROUND: Local anaesthetics (LA) reduce neuronal excitability by inhibiting voltage-gated Na(+) channels. When applied at high concentrations in the direct vicinity of nerves, LAs can also induce relevant irritation and neurotoxicity via mechanisms involving an increase of intracellular Ca(2+). In the present study we explored the role of the Ca(2+)-permeable ion channels TRPA1 and TRPV1 for lidocaine-induced Ca(2+)-influx, neuropeptide release and neurotoxicity in mouse sensory neurons. METHODS: Cultured dorsal root ganglion (DRG) neurons from wildtype and mutant mice lacking TRPV1, TRPA1 or both channels were explored by means of calcium imaging, whole-cell patch clamp recordings and trypan blue staining for cell death. Release of calcitonin gene-related peptide (CGRP) from isolated mouse peripheral nerves was determined with ELISA. RESULTS: Lidocaine up to 10 mM induced a concentration-dependent reversible increase in intracellular Ca(2+) in DRG neurons from wildtype and mutant mice lacking one of the two receptors, but not in neurons lacking both TRPA1 and TRPV1. 30 mM lidocaine also released Ca(2+) from intracellular stores, presumably from the endoplasmic reticulum. While 10 mM lidocaine evoked an axonal CGRP release requiring expression of either TRPA1 or TRPV1, CGRP release induced by 30 mM lidocaine again mobilized internal Ca(2+) stores. Lidocaine-evoked cell death required neither TRPV1 nor TRPA1. SUMMARY: Depending on the concentration, lidocaine employs TRPV1, TRPA1 and intracellular Ca(2+) stores to induce a Ca(2+)-dependent release of the neuropeptide CGRP. Lidocaine-evoked cell death does not seem to require Ca(2+) influx through TRPV1 or TRPV1.