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Caged vanilloid ligands for activation of TRPV1 receptors by 1- and 2-photon excitation.

ABSTRACT: Nociceptive neurons in the peripheral nervous system detect noxious stimuli and report the information to the central nervous system. Most nociceptive neurons express the vanilloid receptor, TRPV1, a nonselective cation channel gated by vanilloid ligands such as capsaicin, the pungent essence of chili peppers. Here, we report the synthesis and biological application of two caged vanilloids: biologically inert precursors that, when photolyzed, release bioactive vanilloid ligands. The two caged vanilloids, Nb-VNA and Nv-VNA, are photoreleased with quantum efficiency of 0.13 and 0.041, respectively. Under flash photolysis conditions, photorelease of Nb-VNA and Nv-VNA is 95% complete in approximately 40 micros and approximately 125 micros, respectively. Through 1-photon excitation with ultraviolet light (360 nm), or 2-photon excitation with red light (720 nm), the caged vanilloids can be photoreleased in situ to activate TRPV1 receptors on nociceptive neurons. The consequent increase in intracellular free Ca(2+) concentration ([Ca(2+)](i)) can be visualized by laser-scanning confocal imaging of neurons loaded with the fluorescent Ca(2+) indicator, fluo-3. Stimulation results from TRPV1 receptor activation, because the response is blocked by capsazepine, a selective TRPV1 antagonist. In Ca(2+)-free extracellular medium, photoreleased vanilloid can still elevate [Ca(2+)](i), which suggests that TRPV1 receptors also reside on endomembranes in neurons and can mediate Ca(2+) release from intracellular stores. Notably, whole-cell voltage clamp measurements showed that flash photorelease of vanilloid can activate TRPV1 channels in <4 ms at 22 degrees C. In combination with 1- or 2-photon excitation, caged vanilloids are a powerful tool for probing morphologically distinct structures of nociceptive sensory neurons with high spatial and temporal precision.

SUBMITTER: Zhao J

PROVIDER: S-EPMC2536571 | biostudies-literature | 2006 Apr

REPOSITORIES: biostudies-literature

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Caged vanilloid ligands for activation of TRPV1 receptors by 1- and 2-photon excitation.

Zhao Jun J Gover Tony D TD Muralidharan Sukumaran S Auston Darryl A DA Weinreich Daniel D Kao Joseph P Y JP

Biochemistry 20060401 15

Nociceptive neurons in the peripheral nervous system detect noxious stimuli and report the information to the central nervous system. Most nociceptive neurons express the vanilloid receptor, TRPV1, a nonselective cation channel gated by vanilloid ligands such as capsaicin, the pungent essence of chili peppers. Here, we report the synthesis and biological application of two caged vanilloids: biologically inert precursors that, when photolyzed, release bioactive vanilloid ligands. The two caged va ...[more]

PMID: 16605259

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Project description:Capsaicinoids, found in less-than-lethal self-defense weapons, have been associated with respiratory failure and death in exposed animals and people. The studies described herein provide evidence for acute respiratory inflammation and damage to epithelial cells in experimental animals, and provide precise molecular mechanisms that mediate these effects using human bronchiolar and alveolar epithelial cells. Inhalation exposure of rats to pepper sprays (capsaicinoids) produced acute inflammation and damage to nasal, tracheal, bronchiolar, and alveolar cells in a dose-related manner. In vitro cytotoxicity assays demonstrated that cultured human lung cells (BEAS-2B and A549) were more susceptible to necrotic cell death than liver (HepG2) cells. Transcription of the human vanilloid receptor type-1, VR1 or TRPV1, was demonstrated by RT-PCR in all of these cells, and the relative transcript levels were correlated to cellular susceptibility. TRPV1 receptor activation was presumably responsible for cellular cytotoxicity, but prototypical functional antagonists of this receptor were cytotoxic themselves, and did not ameliorate capsaicinoid-induced damage. Conversely, the TRPV1 antagonist capsazepine, as well as calcium chelation by EGTA ablated cytokine (IL-6) production after capsaicin exposure. To address these seemingly contradictory results, recombinant human TRPV1 was cloned and overexpressed in BEAS-2B cells. These cells exhibited dramatically increased cellular susceptibility to capsaicinoids, measured using IL-6 production and cytotoxicity, and an apoptotic mechanism of cell death. Surprisingly, the cytotoxic effects of capsaicin in TRPV1 overexpressing cells were also not inhibited by TRPV1 antagonists or by treatments that modified extracellular calcium. Thus, capsaicin interacted with TRPV1 expressed by BEAS-2B and other airway epithelial cells to cause the calcium-dependent production of cytokines and, conversely, calcium-independent cell death. These results have demonstrated that capsaicinoids contained in pepper spray products produce airway inflammation and cause respiratory epithelial cell death. The mechanisms of these cellular responses to capsaicinoids appear to proceed via distinct cellular pathways, but both pathways are initiated by TRPV1.

Dataset Information

Caged vanilloid ligands for activation of TRPV1 receptors by 1- and 2-photon excitation.

Publications

Caged vanilloid ligands for activation of TRPV1 receptors by 1- and 2-photon excitation.

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