Abstract
The possible functional role of transient receptor potential (TRP) channels was investigated by testing various TRP agonists and antagonists in an isolated rat sinus hair follicle preparation. Extracellular recordings from slowly adapting type II mechanoreceptor units were made. The antagonist capsazepine depressed spontaneous and mechanically evoked activity, with an IC(50) of 82 microM. In one-third of units, capsazepine caused a selective depression of mechanically evoked firing, such that the existing spontaneous firing was interrupted by an absence of activity during the mechanical stimulus. The broad spectrum TRP blocker ruthenium red (30 microM) had inconsistent effects, although in some units a delayed onset (following wash) bursting and paroxysmal firing ensued. The agonist icilin (50-100 microM) had an excitatory effect on spontaneous firing, and (-)-menthol (200 microM) had inconsistent effects. Cinnamaldehyde (1-2 mM) depressed all types of activity equally, mechanically evoked and spontaneous. Camphor (0.5-2 mM) also depressed all types of activity, although it had a preferential effect on spontaneous activity. Capsaicin (1-10 microM) and allyl isothiocyanate (50-100 microM) had no clear effects. These results rule out any role for TRPA1 and TRPV1 channels in mechanotransduction processes of slowly adapting type II mechanoreceptors.