Capsaicin or vanilloid receptors (VRs) participate in the sensation of thermal and inflammatory pain. The cloned (VR1) and native VRs are non-selective cation channels directly activated by noxious heat, extracellular protons and vanilloid compounds. However, considerable attention has focused on identifying other signaling pathways in VR activation, and this search has gained more significance given the findings that VR1 is expressed in non-sensory tissue and may mediate inflammatory rather than acute thermal pain. Protein kinase C (PKC) plays an important role in pain signaling. Targeted deletion of PKC epsilon in mice dramatically attenuates thermal- and acid-induced hyperalgesia. In turn, activation of PKC epsilon potentiates heat-evoked currents in sensory neurons. Further, the algesic peptide, bradykinin, potentiates heat responses, induces depolarization and evokes secretion from vanilloid-sensitive neurons in a PKC-dependent manner. Yet the molecular targets for these effects have not been clearly identified. In this study we will test the hypothesis that the VR is directly activated by PKC -mediated phosphorylation in the absence of any other agonist. We propose that the pro-inflammatory peptide bradykinin induces VR activity and that this occurs via the stimulation of PKC. We will also test the hypothesis that in the phosphorylated state, a subthreshold stimulus will be sufficient to maximally activate the VR. We propose that phosphorylation of the channel functions as a gain control to modulate the efficacy and sensitivity of VR activation. In this way a range of normally benign stimuli will become potent activators of VRs. This research has important implications for understanding the role of VRs in hyperalgesia, chronic pain and other non-sensory functions.
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