TRPA1 and TRPV1 are differentially involved in heat nociception of mice.

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.