ION CHANNELS, RECEPTORS AND TRANSPORTERS Allyl isothiocyanate sensitizes TRPV1 to heat stimulation Yeranddy A. Alpizar & Brett Boonen & Maarten Gees & Alicia Sanchez & Bernd Nilius & Thomas Voets & Karel Talavera Received: 30 July 2013 /Accepted: 31 July 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract The powerful plant-derived irritant allyl isothiocy- anate (AITC, aka mustard oil) induces hyperalgesia to heat in rodents and humans through mechanisms that are not yet fully understood. It is generally believed that AITC activates the broadly tuned chemosensory cation channel transient receptor potential cation channel subfamily A member 1 (TRPA1), triggering an inflammatory response that sensitizes the heat sensor transient receptor potential cation channel subfamily V member 1 (TRPV1). In the view of recent data demonstrating that AITC can directly activate TRPV1, we here explored the possibility that this compound sensitizes TRPV1 to heat stim- ulation in a TRPA1-independent manner. Patch-clamp record- ings and intracellular Ca 2+ imaging experiments in HEK293T cells over-expressing mouse TRPV1 revealed that the increase in channel activation induced by heating is larger in the presence of AITC than in control conditions. The analysis of the effects of AITC and heat on the current–voltage relation- ship of TRPV1 indicates that the mechanism of sensitization is based on additive shifts of the voltage dependence of activa- tion towards negative voltages. Finally, intracellular Ca 2+ imaging experiments in mouse sensory neurons isolated from Trpa1 KO mice yielded that AITC enhances the response to heat, specifically in the subpopulation expressing TRPV1. Furthermore, this effect was strongly reduced by the TRPV1 inhibitor capsazepine and virtually absent in neurons isolated from double Trpa1 /Trpv1 KO mice. Taken together, these findings demonstrate that TRPV1 is a locus for cross sensitization between AITC and heat in sensory neurons and may help explaining, at least in part, the role of this channel in AITC-induced hyperalgesia to heat. Keywords Mustard oil . Capsaicin receptor . Hyperalgesia . Sensitization Introduction Allyl isothiocyanate (AITC or mustard oil) is a natural pun- gent compound [30] with ample use in the kitchen and tradi- tional medicine [25]. Since many years, AITC has been employed experimentally to provoke irritation and local in- flammation, and it is particularly well known for its ability to induce strong sensitization of the responses to heat [31]. Therefore, this compound has been frequently used to study the mechanisms underlying thermal hyperalgesia in rodents [8, 10, 13, 20, 22, 29, 33, 34, 41] and humans [1, 15]. A pioneering study [3] proposed that several mouse behav- ioral responses to AITC, including sensitization to heat 1.5– 2 h after topical AITC application, were fully mediated by the broadly tuned chemo-nociceptor transient receptor potential cation channel subfamily A member 1 (TRPA1) [26, 35]. Intriguingly, other studies showed that AITC-induced sensiti- zation to heat is strongly reduced by genetic ablation [5, 10] or pharmacological inhibition [13] of the capsaicin receptor tran- sient receptor potential cation channel subfamily V member 1 (TRPV1). A way to reconcile these data is to propose that TRPA1 acts as the primary sensor of AITC, which triggers an inflammatory response that sensitizes TRPV1 to heat [3]. This seems indeed a very plausible scenario for the maintenance of hyperalgesia to heat hours after application of AITC. However, recent reports showed that TRPV1 is directly acti- vated by AITC at pharmacologically relevant concentrations [11, 28] and that AITC sensitizes TRPV1 to low extracellular pH [14]. In this study, we tested the possibility that AITC Y. A. Alpizar : B. Boonen : M. Gees : A. Sanchez : B. Nilius : T. Voets : K. Talavera Laboratory for Ion Channel Research, Department of Cellular and Molecular Medicine and TRP Research Platform Leuven (TRPLe), KU Leuven, 3000 Leuven, Belgium K. Talavera (*) Laboratory of Ion Channel Research, Department of Cellular and Molecular Medicine, KU Leuven, Herestraat 49. Campus Gasthuisberg, O&N1, 3000 Leuven, Belgium e-mail: Karel.talavera@med.kuleuven.be Pflugers Arch - Eur J Physiol DOI 10.1007/s00424-013-1334-9