title: Activation of transient receptor potential vanilloid 1 (TRPV1) by resiniferatoxin.
abstract: Transient receptor potential vanilloid 1 (TRPV1) is a Ca(2+) permeable non-selective cation channel activated by physical and chemical stimuli. Resiniferatoxin (RTX), an ultrapotent agonist of TRPV1, is under investigation for treatment of urinary bladder hyper-reflexia and chronic pain conditions. Here, we have determined the characteristics of RTX-induced responses in cells expressing native and cloned rat TRPV1. Whole-cell currents increase with repeated application of submaximal concentrations of RTX until a maximal response is attained and do not deactivate even after prolonged washout. Interestingly, the rate of activation and block by capsazepine of RTX-induced currents are significantly slower than for capsaicin-induced currents. RTX-induced whole-cell currents are outwardly rectifying, but to a lesser extent than capsaicin-induced currents. RTX-induced single channel currents exhibit multiple conductance states and outward rectification. The open probability (P(o)) of RTX-induced currents is higher at all potentials as compared to capsaicin-induced currents, which showed a strong voltage-dependent decrease at negative potentials. Single-channel kinetic analyses reveal that open-time distribution of RTX-induced currents can be fitted with three exponential components at negative and positive potentials. The areas of distribution of the longer open time constants are significantly larger than capsaicin-induced currents. The closed-time distribution of RTX-induced currents can be fitted with three exponential components as compared to capsaicin-induced currents, which require four exponential components. Current-clamp experiments reveal that low concentrations of RTX caused a slow and sustained depolarization beyond threshold while generating few action potentials. Concentrations of capsaicin required for the same extent of depolarization generated a significantly greater number of action potentials. These properties of RTX may play a role in its clinical usefulness.
authors.affiliation: Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, 62702, USA.
authors.forename: Manish
authors.initials: M
authors.lastname: Raisinghani
authors.forename: Reddy M
authors.initials: RM
authors.lastname: Pabbidi
authors.forename: Louis S
authors.initials: LS
authors.lastname: Premkumar
mesh_terms: D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D004224:Diterpenes / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000502:physiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D050916:TRPV Cation Channels / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014981:Xenopus
chemical_list: D004224:Diterpenes; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; C024353:resiniferatoxin; D002211:Capsaicin