Sensitization of vanilloid receptor involves an increase in the phosphorylated form of the channel

Abstract

A vanilloid receptor (VR1, now known as TRPV1) is an ion channel activated by vanilloids, including capsaicin (CAP) and resiniferatoxin (RTX), which are pungent ingredients of plants. Putative endogenous activators (anandamide and metabolites of arachidonic acid) are weak activators of VR1 compared to capsaicin and RTX, and the concentrations of the physiological condition of those activators are not sufficient to induce significant activation of VR1. One way to overcome the weak activation of endogenous activators would be the sensitization of VR1, with the phosphorylation of the channel being one possibility. The phosphorylation of VR1 by several kinases has been reported, mostly by indirect evidence. Here, using an in vivo phosphorylation method, the VR1 channel was shown to be sensitized by phosphorylation of the channel itself by multiple pathways involving PKA, PKC and acid. Also, in sensitizing VR1, BK appeared to show activation of PKC for the sensitization of VR1 by phosphorylation of the channel.

Sensory and Signaling Mechanisms of Bradykinin, Eicosanoids, Platelet-Activating Factor, and Nitric Oxide in Peripheral Nociceptors

“…Bradykinin was shown to cause translocation of PKC in cultured DRG neurons (746). Considerable evidence has been provided for the involvement of PKC in the various excitatory (nocifensive or spikegenerating) and sensitizing effects of bradykinin studying transfected cells, cultured sensory neurons (85,94,95,120,296,411,435,585,586,685,745,764; see details in sect. IIC3), nerve fiber discharge (252,253,497), nocifensive behavior (186), and neuropeptide release (200).…”

“…TRPV1 with point mutations introduced at these sites failed to be sensitized to either capsaicin or heat in response to PMA. With the use of an in vitro phosphorylation method on transfected cells and activators of either PKC or PKA, phosphorylation and sensitization of TRPV1 to capsaicin was shown, while bradykinin phosphorylated and activated TRPV1 essentially through PKC (411). In rat DRG neurons, the bradykinin-induced enhancement of the capsaicin-evoked, i.e., TRPV1-mediated, inward current was abolished by either a peptide inhibiting the interaction of the scaffolding protein AKAP79/150 with TRPV1 or by downregulating the expression of AKAP79 by the use of siRNA (794).…”

Regulation of the Benzamil-Insensitive Salt Taste Receptor by Intracellular Ca2+, Protein Kinase C, and Calcineurin

“…To test the hypothesis that PMA, cyclosporin A, and FK-506 alter TRPV1t activity by changing the phosphorylation state of the channel, direct evidence for TRPV1t/TRPV1 phosphorylation was obtained using an in vitro method (Lee et al 2005). Rat lingual epithelium containing fungiform papillae was isolated as described before ).…”

“…We used an in vitro phosphorylation method (Lee et al 2005) to directly demonstrate that following treatment with cyclosporin A or FK-506 (50 ϫ 10 Ϫ6 M each; Fig. 4B) or PMA (25 ϫ 10 Ϫ6 M; Fig.…”

“…It is likely that these differences between the two receptors may be explained by the fact that, unlike TRPV1, TRPV1t is constitutively active at resting TRC membrane potential and normal temperature in the oral cavity. In one study (Lee et al 2005) PMA-treated HEK293 cells, transfected with TRPV1, were found to be permeable to Ca 2ϩ in the absence of TRPV1 agonists. It is likely that PKCdependent phosphorylation of the channel might decrease the temperature threshold of TRPV1.…”