Anandamide induces cough in conscious guinea‐pigs through VR1 receptors

Abstract

Endogenous neuronal lipid mediator anandamide, which can be synthesized in the lung, is a ligand of both cannabinoid (CB) and vanilloid receptors (VR). The tussigenic effect of anandamide has not been studied. The current study was designed to test the direct tussigenic effect of anandamide in conscious guinea‐pigs, and its effect on VR1 receptor function in isolated primary guinea‐pig nodose ganglia neurons. Anandamide (0.3–3 mg·ml−1), when given by aerosol, induced cough in conscious guinea‐pigs in a concentration dependent manner. When guinea‐pigs were pretreated with capsazepine, a VR1 antagonist, the anandamide‐induced cough was significantly inhibited. Pretreatment with CB1 (SR 141716A) and CB2 (SR 144528) antagonists had no effect on anandamide‐induced cough. These results indicate that anandamide‐induced cough is mediated through the activation of VR1 receptors. Anandamide (10–100 μM) increased intracellular Ca2+ concentration estimated by Fluo‐4 fluorescence change in isolated guinea‐pig nodose ganglia cells. The anandamide‐induced Ca2+ response was inhibited by two different VR1 antagonists: capsazepine (1 μM) and iodo‐resiniferatoxin (I‐RTX, 0.1 μM), indicating that anandamide‐induced Ca2+ response was through VR1 channel activation. In contrast, the CB1 (SR 141716A, 1 μM) and CB2 (SR 144528, 0.1 μM) receptor antagonists had no effect on Ca2+ response to anandamide. In conclusion, these results provide evidence that anandamide activates native vanilloid receptors in isolated guinea‐pig nodose ganglia cells and induces cough through activation of VR1 receptors. British Journal of Pharmacology (2002) 137, 831–836. doi:

Mechanistic studies of acid-evoked coughing in anesthetized guinea pigs

“…Not surprisingly, therefore, citric acid-induced coughing was unaffected by pretreatment with atropine, the ␤-agonists albuterol and isoproterenol, the cyclooxygenase inhibitor indomethacin, the bradykinin B2 receptor antagonist FR-173657, the combination of pyrilamine and ICI-198615 (histamine and cysteinyl-leukotriene receptor antagonists, respectively), or depletion of extracellular Ca 2ϩ . This reveals an additional distinction between airway C fibers and the cough receptors, because airway C fibers can be directly activated by some autacoids [e.g., 5-HT, adenosine, bradykinin, ATP, anandamide, 15-HETE (23,25,37,56)] and sensitized by others [e.g., bradykinin, histamine, PGE2, adrenaline (8,13,17,19,30,36)]. Rather, the effects of acid on the cough receptors appeared to be direct.…”

“…In conscious guinea pigs, citric acid-evoked coughing is inhibited by the capsaicin receptor transient receptor potential vanilloid type 1 (TRPV1) antagonists capsazepine and iodo-resiniferatoxin or the TRPV1 channel blocker Ruthenium Red, and can also be inhibited by neurokinin 1 (NK 1 ), NK 2 , and/or NK 3 receptor antagonists (1,2,7,18,34,54,55). The acid-evoked coughing is mimicked by inhalation of the TRPV1 receptor agonists capsaicin, resiniferatoxin, and anandamide in both animals and human subjects, and prior capsaicin desensitization abolishes citric acid-evoked coughing in awake guinea pigs (10,25,35,50). Because the only tachykinin-containing nerves innervating the airways of normal, uninflamed guinea pigs are capsaicinsensitive C fibers (21, 32 49, 56), these data provide overwhelming evidence that acid-evoked coughing in conscious guinea pigs is dependent on activation of capsaicin-sensitive, tachykinin-containing vagal afferent C fibers innervating the airways.…”

Functional TRPV4 channels are expressed in human airway smooth muscle cells

“…Intracellular Ca 2ϩ concentration in cultured HBSMC was measured using the fluorometric imaging plate reader (FLIPR) technique as described previously (17,18). Briefly, cells were incubated with the Ca 2ϩ -sensitive fluorescence dye fluo 4-AM (5 g/ml; Molecular Probes, Eugene, OR) in HBSS (GIBCO) containing 0.4% BSA for 45 min at 37°C.…”

TRPV4 calcium entry channel: a paradigm for gating diversity

“…TRPV4 is expressed in a broad range of tissues, including lung, spleen, kidney, testis, fat, brain, cochlea, skin, smooth muscle, liver, and vascular endothelium (10,18,37,42,74,99). In situ hybridization in the brain indicates expression, in the lamina terminalis of the mouse brain, in neurons of the arched vascular organ of the lamina terminalis, in the median preoptic area, the optic chiasm, neurons of the subfornical organ, the ventral hippocampal commissure, anterior hypothalamic structures, ependymal cells of the choroid plexus in the lateral ventricles, and dorsal root ganglia (DRG) neurons (14,42,74).…”