cyclic-gmp and resiniferatoxin

In the isolated rat mesenteric bed, the 1 min perfusion with 100 nm anandamide, a concentration that did not evoke vasorelaxation, elicited an acute release of 165.1 +/- 9.2 pmol nitric oxide (NO) that was paralleled by a 2-fold increase in cGMP tissue levels. The rise in NO released was mimicked by either (R)-(+)-methanandamide or the vanilloid receptor agonists resiniferatoxin and (E)-capsaicin but not by its inactive cis-isomer (Z)-capsaicin. The NO release elicited by either anandamide or capsaicin was reduced by the TRPV1 receptor antagonists 5'-iodoresiniferatoxin, SB 366791 and capsazepine as well as by the cannabinoid CB(1) receptor antagonists SR 141716A or AM251. The outflow of NO elicited by anandamide and capsaicin was also reduced by endothelium removal or NO synthase inhibition, suggesting the specific participation of endothelial TRPV1 receptors, rather than the novel endothelial TRPV4 receptors. Consistently, RT-PCR showed the expression of the mRNA coding for the rat TRPV1 receptor in the endothelial cell layer, in addition to its expression in sensory nerves. The participation of sensory nerves on the release of NO was precluded on the basis that neonatal denervation of the myenteric plexus sensory nerves did not modify the pattern of NO release induced by anandamide and capsaicin. We propose that low concentrations of anandamide, devoid of vasorelaxing effects, elicit an acute release of NO mediated predominantly by the activation of endothelial TRPV1 receptors whose physiological significance remains elusive.

Topics: Anilides; Animals; Arachidonic Acids; Cannabinoid Receptor Antagonists; Capsaicin; Cinnamates; Cyclic GMP; Diterpenes; Dose-Response Relationship, Drug; Endocannabinoids; Endothelium, Vascular; In Vitro Techniques; Male; Mesenteric Artery, Superior; Nitric Oxide; Nitroarginine; Perfusion; Piperidines; Polyunsaturated Alkamides; Pyrazoles; Rats; Rats, Sprague-Dawley; Rimonabant; RNA, Messenger; TRPV Cation Channels; Vasodilation

The mechanism of activation of sensory neurons by the potent irritant resiniferatoxin (RTX) was compared with that of the pungent compound, capsaicin. RTX and capsaicin evoked an inward, depolarising current associated with an increase in membrane conductance in a subpopulation of dissociated cultured neurons from rat dorsal root ganglia. RTX also evoked an uptake of 45Ca into and an efflux of [14C]guanidinium and of 86Rb from these cells but was at least 100-fold more potent than capsaicin. The levels of cGMP, but not cAMP were elevated by RTX. Prolonged exposure to RTX damaged DRG neurons by a predominantly osmotic process. RTX-sensitive cells were identified by a cobalt-staining method; neurofilament-containing DRG neurons were RTX-insensitive as were all sympathetic neurons and non-neuronal cells. Cultured DRG neurons from chick embryos were also unaffected by RTX. In a neonatal rat spinal cord-tail preparation in vitro, RTX activated capsaicin-sensitive peripheral nociceptive fibres and caused a subsequent spinal cord depolarization measured in the ventral spinal roots. Neither prolonged exposure to a phorbol ester, to desensitize/down-regulate protein kinase C, nor inhibition of protein kinase C by staurosporine affected responses produced by RTX or capsaicin. The effects of capsaicin were abolished when preparations were exposed to desensitizing concentrations of RTX. RTX therefore acts as a highly potent capsaicin analogue to activate a subpopulation of rat sensory neurons.

Topics: Animals; Bradykinin; Calcium; Capsaicin; Cell Survival; Cells, Cultured; Chickens; Cyclic AMP; Cyclic GMP; Diterpenes; Ganglia, Spinal; Guanidine; Guanidines; Kinetics; Membrane Potentials; Neurons; Neurons, Afferent; Neurotoxins; Rats; Rubidium