Anti-Histaminergic Responses On TRPV1 Channels

S U N D A Y 481 Anti-Histaminergic Responses On TRPV1 Channels Umesh Singh, Jonathan A. Bernstein, MD, Kristin Luther, Lauren Haar, W. Keith Jones; University of Cincinnati, Cincinnati, OH, Bernstein Allergy Group, Cincinnati, OH, University of Cincinnati Medical Center, Cincinnati, OH. RATIONALE: Activation of sensory neurons are known to be mediated by TRPV1 ion channels which may contribute to the pathophysiology of neurogenic inflammation. Recently we demonstrated that the topical antihistamine, azelastine (AZL), reported effective in non-allergic rhinitis (NAR), activates TRPV1 ion channels. The purpose of this study was to elucidate the effect of AZL on TRPV1 signaling. METHODS: Mice neuronal cells (CATH.a) were plated on glass coverslips and incubated (378C/5%CO2 324 hrs.). After loading cells with Ca2+ specific fluorescent dye Fluo-4 AM, changes in free cytosolic Ca2+([Ca2+]i), in response to AZL 30 mM and the TRPV1 agonist, Capsaicin 1 mM (CAP) , were assessed by confocal imaging. RT-PCR for mRNA expression of protein kinases (PKA and PKC) and phospholipase C (PLC) were performed to assess for TRPV1 responses recovering from desensitization. RESULTS: Sustained pre-treatment (;15 minutes) of CATH.a cells with CAP (1 mM) or AZL (30 mM) made these cells refractory to further increase in [Ca2+]i after subsequent applications of these agents indicating desensitization of TRPV1. After allowing for TRPV1 channel recovery (;25 minutes) from the desensitized state, treatment with either CAP (1 mM) or AZL (30 mM) resulted in a significant increase in [Ca2+]i which correlated with increased mRNA expression of the phosphorylating proteins PKA, PKC and PLC associated with re-sensitization of TRPV1. CONCLUSIONS: Sustained application of either CAP or AZL desensitize TRPV1 ion channels. This data could explain the therapeutic effect of AZL in NAR thought to be caused by neurogenic inflammation.