Despite intense efforts to effectively treat acute and chronic pain, current therapies are still associated with significant side effects including central nervous system depression, development of tolerance and risk of addiction. Since the majority of acute and chronic pain is maintained by the persistent activation of specialized sensory neurons, the selective blockade of pain sensing nerve terminals could represent a novel way to treat pain with fewer unwanted side effects. Recent advances have been made in the characterization of receptors and ion channels that function to detect painful noxious stimuli. Notably, the vanilloid (capsaicin) receptorVR1 has been isolated and is undergoing intense characterization to determine whether it can direct sensory nerve activation in response to painful stimuli. Because the response properties of sensory neurons are complex, we have investigated whether other related receptor / ion channels exist in sensory neurons. This effort has revealed the existence of vanilloid receptor splice variants. VR.5'sv is one such variant that we isolated that appears insensitive to capsaicin and other noxious stimuli. In this proposal, we are testing the hypothesis that VR.5'sv can block the activation of VR1 in response to noxious stimuli when both proteins are expressed together. Another vanilloid receptor splice variant originally identified in kidney by another laboratory was found to have mechano-sensitive properties and therefore is termed """"""""stretch inactivated channel."""""""" SIC is activated by cell shrinkage, and based on its pattern of expression in sensory neurons, it may participate in the detection of noxious hypertonic conditions. Comparison of SIC to VR1 and VR.5'sv has revealed a unique structural feature that could help explain its ability to couple changes in cell shape into channel activation. We propose to study this feature in the hope to better understand how noxious mechanical stimuli are detected by sensory neurons. Although our understanding about VR1 and its splice variants have grown, little is known about what factors control their abundance in the sensory nerve terminals. Using genomic fragments isolated upstream from the vanilloid receptor gene and inserted into reporter plasmids, we will test the hypothesis that tissue derived growth factors positively regulate the amount of RNA encoding VR1 in sensory neurons through their effect on RNA transcription. Moreover, using this assay system, we hope to determine in general what factors regulate VR1, VR.5' sv and SIC. Determining bow these factors increase or decrease the transcription of VR subtypes will provide a potential means to modulate pain transduction and hyperalgesia.
