Hydrogen sulfide activates TRPA1 and releases 5-HT from epithelioid cells of the chicken thoracic aorta

Epithelioid cells in the chicken thoracic aorta are chemoreceptor cells that release 5-HT in response to hypoxia. It is likely that these cells play a role in chemoreception similar to that of glomus cells in the carotid bodies of mammals. Recently, H2S was reported to be a key mediator of carotid glomus cell responses to hypoxia. The aim of the present study was to reveal the mechanism of action of H2S on 5-HT outflow from chemoreceptor cells in the chicken thoracic aorta. The 5-HT outflow induced by NaHS, an H2S donor, and Na2S3, a polysulfide, was measured by using a HPLC equipped with an electrochemical detector. NaHS (0.3-3 mM) caused a concentration-dependent increase in 5-HT outflow, which was significantly inhibited by the removal of extracellular Ca2+. outflow induced by NaHS (0.3 mM) was also significantly inhibited by voltage-dependent L- and N-type Ca2+ channel blockers and a selective TRPA1 channel blocker. Cinnamaldehyde, a TRPA1 agonist, mimicked the secretory response to H2S. 5-HT outflow induced by Na2S3 (10 M) was also inhibited by the TRPA1 channel blocker. Furthermore, the expression of TRPA1 was localized to 5-HT-containing chemoreceptor cells in the aortic wall. These findings suggest that the activation of TRPA1 and voltage-dependent Ca2+ channels is involved in H2S-evoked 5-HT release from chemoreceptor cells in the chicken aorta. (C) 2016 Elsevier Inc. All rights reserved

A mechanically activated ion channel is functionally expressed in the MrgprB4 positive sensory neurons, which detect stroking of hairy skin in mice

Mas-related G-protein coupled receptor B4 (MrgprB4) has been reported to be expressed in the dorsal root ganglion (DRG) neurons which detect stroking of hairy skin of mice. However, the mechanisms by which the MrgprB4 positive (+) neurons respond to adequate stimulus remain unsolved as it was also reported that electrophysiological analysis of cultured MrgprB4+ neurons did not reveal responses to mechanical stimuli. Contrary to the observation, however, in this study we show that the MrgprB4+ neurons functionally express a mechanically activated channel using DRG neurons dissociated from genetically-modified mice whose MrgprB4+ neurons express a red fluorescent protein. Hypotonicity-induced cell swelling increased intracellular Ca2+ concentrations ([Ca2+]i) of MrgprB4+ neurons. The [Ca2+]i increases were prevented by extracellular Ca2+ removal and by applications of nonselective Piezo channel blockers. Patch clamp analysis revealed that the MrgprB4+ neurons exhibited rapidly-adapting mechanically-activated currents. The MrgprB4+ neurons were stained with anti-Piezo2 antibody. These results raise the possibility that the MrgprB4+ neurons directly detect the stroking-like stimuli of hairy skin

Hydrogen sulfide induces Ca2+ release from intracellular Ca2+ stores and stimulates lactate production in spinal cord astrocytes

Hydrogen sulfide (H2S) is a well-known inhibitor of the mitochondrial electron transport chain (ETC). H2S also increases intracellular Ca2+ levels in astrocytes, which are glial cells and that supply lactate as an energy substrate to neurons. Here, we examined the relationship between H2S-induced metabolic changes and Ca2+ responses in spinal cord astrocytes. H2S (150 mu M), an H2S donor, increased the intracellular Ca2+ concentration, which was inhibited by an ETC inhibitor and an uncoupler of mitochondrial oxidative phosphorylation. H2S also increased the accumulation of extracellular lactate. Na2S alone did not change intracellular ATP content, but decreased it when glycolysis was inhibited. The Na2S-induced Ca2+ increase and accumulation of extracellular lactate were inhibited by emetine, an inhibitor of translocon complex, which mediates Ca2+ leak from the endoplasmic reticulum (ER). Furthermore, an inhibitor of the Ca2+-sensitive NADH shuttle decreased H2S-mediated accumulation of lactate. We conclude that inhibition of the mitochondrial ETC by H2S induces Ca2+ release from mitochondria and the ER in spinal cord astrocytes, which increases lactate production. H2S may promote glycolysis by activating the Ca2+-sensitive NADH shuttle and facilitating the supply of lactate from astrocytes to neurons. (C) 2021 Elsevier B.V. and Japan Neuroscience Society. All rights reserved

Contribution of α2A-adrenoceptor subtype to effect of dexmedetomidine and xylazine on spinal synaptic transmission of mice

Alpha-2A adrenergic receptor (AR) subtype plays an important role in the analgesic effect of α2-AR agonists. Here, we examined the effects of α2-AR agonists, dexmedetomidine and xylazine, on spinal synaptic transmission in newborn C57BL/6J and α2A-AR mutant mice. Spinal reflex potentials, the monosynaptic reflex potential (MSR) and the slow ventral root potential (sVRP), were measured in isolated spinal cords. The compound action potential was measured in isolated lumbar nerve. Dexmedetomidine and xylazine suppressed both the MSR and sVRP in a concentration-dependent manner. In α2A-AR mutant mice, sVRP suppression by dexmedetomidine was greatly weakened, while that by xylazine (30-100μM) showed only slight attenuation. A high concentration (300μM) of xylazine completely suppressed the sVRP, even in α2A-AR mutant mice spinal cords, and also suppressed the compound action potential. MSR suppression by these α2-AR agonists had no difference between wild-type and α2A-AR mutant mice. These results suggest that sVRP suppression by dexmedetomidine and xylazine is mainly mediated by α2A-AR. In addition, a high concentration of xylazine inhibits conduction of the action　potential, which is not mediated by α2A-AR. α2-AR is not responsible for the dexmedetomidine- and xylazine-mediated inhibition of the MSR. (C) 2015 Elsevier B.V. All rights reserved

Alpha and beta adrenoceptors activate interleukin-6 transcription through different pathways in cultured astrocytes from rat spinal cord

In brain astrocytes, noradrenaline (NA) has been shown to up-regulate IL-6 production via 13-adrenoceptors (ARs). However, the underlying intracellular mechanisms for this regulation are not clear, and it remains unknown whether ?-ARs are involved. In this study, we investigated the AR-mediated regulation of IL-6 mRNA levels in the cultured astrocytes from rat spinal cord. NA, the ?1-agonist phenylephrine, and the 13-agonist isoproterenol increased IL-6 mRNA levels. The phenylephrine-induced IL-6 increase was accompanied by an increase in ERK phosphorylation, and these effects were blocked by inhibitors of PKC and ERK. The isoproterenol-induced IL-6 increase was accompanied by an increase in CREB phosphorylation, and these effects were blocked by a PKA inhibitor. Our results indicate that IL-6 increases by ?1- and 13-ARs are mediated via the PKC/ERK and cAMP/PKA/CREB pathways, respectively. Moreover, conditioned medium collected from astrocytes treated with the ?2-AR agonist dexmedetomidine, increased IL-6 mRNA in other astrocytes. In this study, we elucidate that ?1- and ?2-ARs, in addition to 13-ARs, promote IL-6 transcription through different pathways in spinal cord astrocytes

Hydrogen sulfide induces Ca2+ release from the endoplasmic reticulum and suppresses ATP-induced Ca2+ signaling in rat spinal cord astrocytes

Hydrogen sulfide (H2S) has a variety of physiological functions. H2S reportedly increases intracellular Ca2+ concentration ([Ca2+];) in astrocytes. However, the precise mechanism and functional role of this increase are not known. Here, we examined the effects of H2S on [Ca2+]; in astrocytes from the rat spinal cord and whether H2S affects ATP-induced Ca2+ signaling, which is known to be involved in synaptic function. Na2S (150 mu M), an H2S donor, produced a nontoxic increase in [Ca2+];. The [Ca2+]; increase by Na2S was inhibited by Ca2+ depletion in the endoplasmic reticulum (ER) but not by removal of extracellular Ca2+, indicating that H2S releases Ca2+ from the ER. On the other hand, (NaS)-S-2 inhibited ATP-induced [Ca2+]; increase when Na2S clearly increased [Ca2+]; in the astrocytes, which was not suppressed by a reducing agent. In addition, Na2S had no effect on intracellular cyclic AMP (cAMP) level. These results indicate that oxidative post-translational modification of proteins and cAMP are not involved in the inhibitory effect of H2S on ATP-induced Ca2+ signaling. We conclude that H2S indirectly inhibits ATP-induced Ca2+ signaling by decreasing Ca2+ content in the ER in astrocytes. In this way, H2S may influence intercellular communication between astrocytes and neurons, thereby contributing to neuronal signaling in the nervous system

The alpha(2A)-adrenoceptor subtype plays a key role in the analgesic and sedative effects of xylazine

Xylazine, the classical alpha(2)-adrenoceptor (alpha(2)-AR) agonist, is still used as an analgesic and sedative in veterinary medicine, despite its low potency and affinity for alpha(2)-ARs. Previous pharmacological studies suggested that the alpha(2A)-AR subtype plays a role in mediating the clinical effects of xylazine; however, these studies were hampered by the poor subtype-selectivity of the antagonists used and a lack of knowledge of their bioavailability in vivo. Here, we attempted to elucidate the role of the alpha(2A)-AR subtype in mediating the clinical effects of xylazine by comparing the analgesic and sedative effects of this drug in wild-type mice with those in alpha(2A)-AR functional knockout mice using the hot-plate and open field tests, respectively. Hippocampal noradrenaline turnover in both mice was also measured to evaluate the contribution of alpha(2A)-AR subtype to the inhibitory effect of xylazine on presynaptic noradrenaline release. In wild-type mice, xylazine (10 or 30 mg/kg) increased the hot-plate latency. Furthermore, xylazine (3 or 10 mg/kg) inhibited the open field locomotor activity and decreased hippocampal noradrenaline turnover. By contrast, all of these effects were abolished in alpha(2A)-AR functional knockout mice. These results indicate that the alpha(2A)-AR subtype is mainly responsible for the clinical effects of xylazine