The pain and hyperalgesia associated with persistent inflammation are due, at least in part, to an increase in excitability and transmitter release from both peripheral and central terminals of nociceptive afferents. We have previously reported that the evoked Ca2+ transients in these sensory neurons are bigger and longer lasting in the presence of persistent inflammation. While we have previously ruled out a number of mechanisms that may contribute to the inflammation-induced changes in the regulation of Ca2+ in nociceptive afferents, my preliminary results indicate two distinct mechanisms that underlie these changes. One is an inflammation- induced decrease in the activity of a Na+/Ca2+ exchanger (NCX), a mechanism of Ca2+ extrusion and suggested to be the basis for the inflammation-induced decrease in the evoked transient decay rate. The second is an inflammation-induced up-regulation of an internal store-mediated Ca2+ influx pathway, which appears to contribute to the increase in magnitude of the evoked Ca2+ transient. In this proposal, I will focus on the first mechanism in a series of experiments designed to test the hypothesis that the maintenance of the inflammatory hypersensitivity is due, at least in part, to a decrease in Na+/Ca2+ exchanger activity in cutaneous nociceptive afferents. I will first determine which NCX isoform(s) are responsible for the inflammation-induced decrease in NCX activity, as all three are expressed in cutaneous nociceptive neurons. I will then determine the basis for the inflammation-induced decrease in NCX activity in cutaneous nociceptive neurons through assessment of expression, density, and distribution of the isoform(s). Finally, I will assess the functional implications of a decrease in NCX activity on the excitability of nociceptive neurons, the neurogenic inflammatory response, and nociceptive behavior. In the proposed experiments, I will employ a complimentary array of in vitro and in vivo assays in combination with siRNA knockdown and pharmacological inhibition of NCX. Thus, the successful completion of the proposed experiments will provide novel information regarding the function of a protein critical for Ca2+ regulation, suggest novel therapeutic approaches for the treatment of inflammatory pain, and provide a solid experimental foundation upon which to build a career as an independent scientist.
Peripheral inflammation is recognized as an overwhelming burden to the health of the US population and the underlying basis of a significant number of diseases such as dermatitis, osteoarthritis, and interstitial cystitis. Our laboratory and others have previously highlighted the impact of inflammation-induced dysregulation of Ca2+ signaling within the primary afferent on pain and hypersensitivity associated with inflammation. Having identified an underlying mechanism of the inflammation-induced dysregulation of Ca2+ signaling, I have proposed to determine the contribution of this mechanism to the inflammatory processes as well as changes in pain and sensitivity. The experiments proposed will provide novel information regarding the regulation of Ca2+ in sensory neurons critical for the perception of pain and may suggest novel therapeutic approaches for the treatment of pain.