The Oxford Handbook of the Neurobiology of Pain, 2019
The K+ channel family is one of the most complex families of ion channels. The diversity of this ... more The K+ channel family is one of the most complex families of ion channels. The diversity of this channel family is a real challenge for the study of pain. Potassium channels form the largest family of ion channels in mammals, with more than 80 genes encoding α subunits in humans. Their differences in structures and functions divide them into four families, all of which are expressed in somatosensory neurons and supporting glial cells. The opening of K+ channels hyperpolarizes the plasma membrane, which opposes excitation of the neuron by all other depolarizing channels. K+ channels are very efficient regulators of the electrical activity of sensory neurons and of pain perception. Their potential for the development of antinociceptive pharmacology is immense.
Two-pore domain background K(+) channels (K2p or KCNK) produce hyperpolarizing currents that cont... more Two-pore domain background K(+) channels (K2p or KCNK) produce hyperpolarizing currents that control cell membrane polarity and neuronal excitability throughout the nervous system. The TREK2 channel as well as the related TREK1 and TRAAK channels are mechanical-, thermal- and lipid-gated channels that share many regulatory properties. TREK2 is one of the major background channels expressed in rodent nociceptive neurons of the dorsal root ganglia that innervate the skin and deep body tissues, but its role in somatosensory perception and nociception has remained poorly understood. We now report that TREK2 is a regulatory channel that controls the perception of non aversive warm, between 40°C and 46°C, and moderate ambient cool temperatures, between 20°C and 25°C, in mice. TREK2 controls the firing activity of peripheral sensory C-fibers in response to changes in temperature. The role of TREK2 in thermosensation is different from that of TREK1 and TRAAK channels; rather, TREK2, TREK1, and TRAAK channels appear to have complementary roles in thermosensation. TREK2 is also involved in mechanical pain perception and in osmotic pain after sensitization by prostaglandin E2. TREK2 is involved in the cold allodynia that characterizes the neuropathy commonly associated with treatments with the anticancer drug oxaliplatin. These results suggest that positive modulation of the TREK2 channel may have beneficial analgesic effects in these neuropathic conditions.
Molecular determinants of threshold sensitivity of mammalian mechanoreceptors are unknown. Here, ... more Molecular determinants of threshold sensitivity of mammalian mechanoreceptors are unknown. Here, we identify a mechanosensitive (MS) K + current (I Kmech ) that governs mechanical threshold and adaptation of distinct populations of mechanoreceptors. Toxin profiling and transgenic mouse studies indicate that I Kmech is carried by Kv1.1-Kv1.2 heteromers. Mechanosensitivity is attributed to Kv1.1 subunits, through facilitation of voltage-dependent open probability. I Kmech is expressed in highthreshold C-mechano-nociceptors (C-HTMRs) and Ab-mechanoreceptors, but not in low-threshold C-mechanoreceptors. I Kmech opposes depolarization induced by slow/ultraslow MS cation currents in C-HTMRs, thereby shifting mechanical threshold for firing to higher values. However, due to kinetics mismatch with rapidly-adapting MS cation currents, I Kmech tunes firing adaptation but not mechanical threshold in Ab-mechanoreceptors. Expression of Kv1.1 dominant negative or inhibition of Kv1.1/I Kmech caused severe mechanical allodynia but not heat hyperalgesia. By balancing the activity of excitatory mechanotransducers, Kv1.1 acts as a mechanosensitive brake that regulates mechanical sensitivity of fibers associated with mechanical perception.
A specific interaction between the AMPA receptor subunits GluR2 and GluR3 and the fusion protein ... more A specific interaction between the AMPA receptor subunits GluR2 and GluR3 and the fusion protein NSF has recently been identified. Disruption of this interaction by adenoviral-mediated expression of a peptide (pep2m) corresponding to the NSF-binding region of GluR2 results in a dramatic reduction in surface expression of AMPA receptors in primary hippocampal neurons. Here we report that expression of pep2m from a recently developed neuronal-specific adenoviral system gave significant neuroprotection to primary CA1-CA3 hippocampal neurons following stimulation with kainate (KA) and this was accompanied by a reduction in Ca 2؉ influx. Protection was also observed following glucose deprivation and exposure to ischemic buffer in the absence of any NMDA receptor antagonists. These results provide strong evidence that AMPA receptors play a direct role in mediating postischemic neurotoxicity.
A transfer system that enabled the efficient introduction of transgenes into neurones and the qua... more A transfer system that enabled the efficient introduction of transgenes into neurones and the quantitative control of the expressed transgene would greatly facilitate studies into neuronal gene function. To develop such a system we incorporated the tetracycline (Tet)-responsive On/Off regulatory elements into type-5 adenoviral (Ad) vectors. Regulation of transgene expression following transfection was measured by placing the enhanced green fluorescent protein (EGFP) gene upstream of the Tet regulatory element. The results showed that cultures of primary hippocampal cells could be transfected with very high efficiency (<70%) by the AdTet-On and AdTet-Off systems. Following transfection with the AdTet-On system no EGFP-fluorescent cells could be detected until doxycycline was added. The AdTet-Off system showed the reverse transcriptional regulation, in that the addition of Tet caused EGFP fluorescence to be abolished.
TRESK (K2P18.1) is a background K+ channel highly expressed in dorsal root and trigeminal ganglia... more TRESK (K2P18.1) is a background K+ channel highly expressed in dorsal root and trigeminal ganglia sensory neurons, where it has been involved in modulating sensory neuron excitability and firing. Reduction in channel expression and function has been reported to enhance nociceptors excitability after injury or inflammation, but its role in somatosensory perception and nociception is still poorly understood. Here we show that TRESK regulates the sensitivity to mechanical and cold stimuli, but it is not involved in the perception of heat. Small/medium-sized DRG sensory neurons from TRESK knockout mice (KO) present an enhanced excitability and recordings from skin nociceptive C-fibers show an increased activation at lower intensity stimulus in response to cold and mechanical stimulation in the absence of the channel. In agreement, mice lacking TRESK present mechanical and cold hypersensitivity compared to wild-type littermates, while heat sensitivity is unaltered. TRESK is also involved...
Cold temperature detection involves the process of sensory transduction in cutaneous primary sens... more Cold temperature detection involves the process of sensory transduction in cutaneous primary sensory nerve terminals, which converts thermal stimuli into depolarizations of the membrane. This transformation into electrical signals is followed by the subsequent propagation of action potentials in cold-sensitive afferent nerve fibers. A large array of ion channels shapes this process; however, the precise contribution of specific ion channel subtypes to cold perception and cold pain remains elusive. This review aims at giving an update on our current understanding of the role played by TRPs, leak K ϩ and voltage-gated Na ϩ and K ϩ channels in the transduction of cold by nociceptors and in cold-induced pain.
Archives internationales de physiologie, de biochimie et de biophysique
Cells expand energy to lower the concentration of free calcium in the cytosol ([Ca2+]i) to a very... more Cells expand energy to lower the concentration of free calcium in the cytosol ([Ca2+]i) to a very low level. Extracellular Ca2+ entering via channels situated in the plasma membrane is expelled into the extracellular medium by a Ca(2+)-Mg(2+)-ATPase or by Na(+)-Ca2+ exchangers. The Ca2+ that enters the cell is sequestered, once inside the cytosol, by a Ca(2+)-Mg(2+)-ATPase, which concentrates Ca2+ in specialized domains of the endoplasmic reticulum. The nucleus and the mitochondria also concentrate Ca2+, but less efficiently. The stimulation of numerous receptors by hormones, growth factors and neurotransmitters coupled to GTP-binding proteins provokes a rapid increase in [Ca2+]i by mobilizing Ca2+ from intra- and extracellular compartments. Membrane coupling is ensured by the activation of a phospholipase C-beta, which hydrolyses a doubly phosphorylated phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). The inositol (1,4,5)-trisphosphate (InsP3) consequently f...
The effects of the beta-adrenoceptor agonist isoprenaline and cyclic AMP (cAMP) on cytosolic free... more The effects of the beta-adrenoceptor agonist isoprenaline and cyclic AMP (cAMP) on cytosolic free Ca2+ ([Ca2+]i) were studied in the single guinea-pig hepatocyte. In common with InsP3-dependent agonists such as noradrenaline or angiotensin II, isoprenaline (0.5-10 microM) and cAMP (50-100 mM, perfused into the cell via the patch-pipette), were able to generate fast and slow fluctuations of [Ca2+]i. Responses to isoprenaline and cAMP also were observed in the absence of external Ca2+. Isoprenaline-evoked [Ca2+]i rises were not blocked by the intracellular perfusion of heparin, suggesting that these fluctuations are independent of the binding of InsP3 to its receptor.
In liver cells, the stimulation of alpha 1-adrenoceptors by noradrenaline induces the production ... more In liver cells, the stimulation of alpha 1-adrenoceptors by noradrenaline induces the production of Ins(1,4,5)P3 through the degradation of membrane polyphosphoinositides [PtdIns(4,5)P2]. InsP3 evokes in turn the release of Ca2+ from internal stores. Our results show that the internal perfusion of single guinea-pig hepatocytes with monoclonal anti-PtdInsP2 antibody blocks the rise in cytosolic free Ca2+ concn. ([Ca2+]i) evoked by noradrenaline, an InsP3-dependent agonist, but not by the monohydroxylated bile acid taurolithocholate 3-sulphate, which is known to permeabilize the endoplasmic reticulum. In these conditions, the bile acid elicited either fast or slow fluctuations of [Ca2+]i independently of any InsP3 production. The responses to the bile acid were also observed in the absence of external Ca2+. The presence of intracellular anti-PtdInsP2 antibody does not affect the response to a photolytic release of InsP3 (1.5 microM final concn.) from a caged precursor.
ABSTRACT Les cellules dépensent de l'énergie pour baisser la concentration du calcium ion... more ABSTRACT Les cellules dépensent de l'énergie pour baisser la concentration du calcium ionisé cytosolique ([Ca2+]i) à un niveau très bas. Le Ca2+ extracellulaire entrant via les canaux localisés dans la membrane plasmique est rejeté vers le milieu extracellulaire par une Ca2+-Mg2+-ATPase, ou des échangeurs Na+/Ca2+. Le Ca2+ entrant est également séquestré depuis le cytosol par une Ca2+-Mg2+-ATPase qui concentre le Ca2+ dans des domaines spécialisés du reticulum endoplasmique. Le noyau et les mitochondries, avec une efficacité moindre, concentrent également le Ca2+. La stimulation de nombreux récepteurs par des hormones, des facteurs de croissance et des neurotrans-metteurs couplés à des protéines liant le GTP, provoquent une augmentation rapide de la [Ca2+]i en mobilisant le Ca2+ depuis les compartiments intra-et extracellulaires. Le couplage membranaire est assuré par l'activation d'une phospholipase C-β qui hydrolyse un phosphoinositide doublement phosphorylé, le phosphatidylinositol 4,5–bisphosphate (PtdIns(4,5)P2). L'inositol (1,4,5)-trisphosphate (InsP3) formé se fixe sur un récepteur composé de quatre monomères homologues de 250 kDa. Le récepteur de l'InsP, a été localisé dans des régions spécialisées, riches en Ca2+, du reticulum endoplasmique. Le récepteur a été purifié et sa séquence obtenue. Réincorporé dans des bicouches planes, il exprime les propriétés d'un canal. Dans la cellule, l'ouverture du canal-récepteur de l'InsP3 provoque la libération du Ca2+ accumulé dans le reticulum endoplasmique. Les analyses cinétiques, effectuées avec des méthodes de mélange et de filtration rapides ou de photolyse d'InsP3 cagé, ont montré que l'InsP3 ouvre le canal avec un délai très court, probablement inférieur à 20 ms. Le récepteur-canal de l'InsP3 présente des propriétés autorégénératives. Avec la stimulation soutenue de l'influx de Ca2+, la libération du Ca2+ entraîne une augmentation de la [Ca2+]i responsable du déclenchement des réponses cellulaires. Les études utilisant des techniques perf ormantes de détection du Ca2+ ionisé cytosolique telles que les protéines bioluminescentes, les indicateurs fluorescents ou les courants ioniques sensibles au Ca2+, ont révélé la complexité des signaux Ca2+ produits par les cellules stimulées. II est apparu que les variations de la [Ca2+]i induites par une stimulation hormonale sont composées d'oscillations dont la fréquence, et non l'amplitude, est dépendante de la concentration de l'hormone. De plus, la numérisation des images enregistrées par caméra vidéo a permis de mettre en évidence les changements de [Ca2+]i au niveau subcellulaire et les vagues Ca2+ dans les cellules stimulées.
In single liver cells, the D-myo-inositol 1,4,5-triphosphate (InsP3)-dependent agonists such as n... more In single liver cells, the D-myo-inositol 1,4,5-triphosphate (InsP3)-dependent agonists such as noradrenaline and angiotensin II evoke oscillations in intracellular calcium [Ca2+]i resulting mostly from the periodic release and reuptake of calcium from intracellular stores. In the present work, we have reexamined the effects of these agonists and investigated whether the natural bile acid taurolithocholic acid 3-sulfate (TLC-S), which permeabilizes the endoplasmic reticulum, could initiate oscillations of [Ca2+]i. Oscillations of [Ca2+]i were monitored with the Ca2(+)-dependent K+ permeability in whole-cell voltage-clamped guinea pig liver cells. Our results confirm the presence of two types of oscillations induced by hormones. They could be distinguished by their frequency periods. The fast (type I) had periods ranging from 5 to 12 s and the slow (type II) from 60 to 240 s. They have been respectively attributed to second messenger- and receptor-controlled oscillations, respectively. Our results also show that TLC-S, as noradrenaline and angiotensin II, induced the activation of this Ca(+)-dependent K+ current and was able to reproduce both types of oscillations. The bile acid effect was not blocked by intracellular perfusion of heparin known to inhibit both InsP3 binding and InsP3-evoked Ca2+ release in several tissues. In these conditions, TLC-S only evoked type I oscillations, suggesting that these fluctuations could originate from a mechanism that is independent of InsP3 and is an intrinsic property of internal Ca2+ stores.
Implication des canaux ioniques dans l'hypersensibilité au froid induite par l'oxaliplatine Oxali... more Implication des canaux ioniques dans l'hypersensibilité au froid induite par l'oxaliplatine Oxaliplatin-induced cold hypersensitivity is due to remodeling of ion channels in nociceptors
The Oxford Handbook of the Neurobiology of Pain, 2019
The K+ channel family is one of the most complex families of ion channels. The diversity of this ... more The K+ channel family is one of the most complex families of ion channels. The diversity of this channel family is a real challenge for the study of pain. Potassium channels form the largest family of ion channels in mammals, with more than 80 genes encoding α subunits in humans. Their differences in structures and functions divide them into four families, all of which are expressed in somatosensory neurons and supporting glial cells. The opening of K+ channels hyperpolarizes the plasma membrane, which opposes excitation of the neuron by all other depolarizing channels. K+ channels are very efficient regulators of the electrical activity of sensory neurons and of pain perception. Their potential for the development of antinociceptive pharmacology is immense.
Two-pore domain background K(+) channels (K2p or KCNK) produce hyperpolarizing currents that cont... more Two-pore domain background K(+) channels (K2p or KCNK) produce hyperpolarizing currents that control cell membrane polarity and neuronal excitability throughout the nervous system. The TREK2 channel as well as the related TREK1 and TRAAK channels are mechanical-, thermal- and lipid-gated channels that share many regulatory properties. TREK2 is one of the major background channels expressed in rodent nociceptive neurons of the dorsal root ganglia that innervate the skin and deep body tissues, but its role in somatosensory perception and nociception has remained poorly understood. We now report that TREK2 is a regulatory channel that controls the perception of non aversive warm, between 40°C and 46°C, and moderate ambient cool temperatures, between 20°C and 25°C, in mice. TREK2 controls the firing activity of peripheral sensory C-fibers in response to changes in temperature. The role of TREK2 in thermosensation is different from that of TREK1 and TRAAK channels; rather, TREK2, TREK1, and TRAAK channels appear to have complementary roles in thermosensation. TREK2 is also involved in mechanical pain perception and in osmotic pain after sensitization by prostaglandin E2. TREK2 is involved in the cold allodynia that characterizes the neuropathy commonly associated with treatments with the anticancer drug oxaliplatin. These results suggest that positive modulation of the TREK2 channel may have beneficial analgesic effects in these neuropathic conditions.
Molecular determinants of threshold sensitivity of mammalian mechanoreceptors are unknown. Here, ... more Molecular determinants of threshold sensitivity of mammalian mechanoreceptors are unknown. Here, we identify a mechanosensitive (MS) K + current (I Kmech ) that governs mechanical threshold and adaptation of distinct populations of mechanoreceptors. Toxin profiling and transgenic mouse studies indicate that I Kmech is carried by Kv1.1-Kv1.2 heteromers. Mechanosensitivity is attributed to Kv1.1 subunits, through facilitation of voltage-dependent open probability. I Kmech is expressed in highthreshold C-mechano-nociceptors (C-HTMRs) and Ab-mechanoreceptors, but not in low-threshold C-mechanoreceptors. I Kmech opposes depolarization induced by slow/ultraslow MS cation currents in C-HTMRs, thereby shifting mechanical threshold for firing to higher values. However, due to kinetics mismatch with rapidly-adapting MS cation currents, I Kmech tunes firing adaptation but not mechanical threshold in Ab-mechanoreceptors. Expression of Kv1.1 dominant negative or inhibition of Kv1.1/I Kmech caused severe mechanical allodynia but not heat hyperalgesia. By balancing the activity of excitatory mechanotransducers, Kv1.1 acts as a mechanosensitive brake that regulates mechanical sensitivity of fibers associated with mechanical perception.
A specific interaction between the AMPA receptor subunits GluR2 and GluR3 and the fusion protein ... more A specific interaction between the AMPA receptor subunits GluR2 and GluR3 and the fusion protein NSF has recently been identified. Disruption of this interaction by adenoviral-mediated expression of a peptide (pep2m) corresponding to the NSF-binding region of GluR2 results in a dramatic reduction in surface expression of AMPA receptors in primary hippocampal neurons. Here we report that expression of pep2m from a recently developed neuronal-specific adenoviral system gave significant neuroprotection to primary CA1-CA3 hippocampal neurons following stimulation with kainate (KA) and this was accompanied by a reduction in Ca 2؉ influx. Protection was also observed following glucose deprivation and exposure to ischemic buffer in the absence of any NMDA receptor antagonists. These results provide strong evidence that AMPA receptors play a direct role in mediating postischemic neurotoxicity.
A transfer system that enabled the efficient introduction of transgenes into neurones and the qua... more A transfer system that enabled the efficient introduction of transgenes into neurones and the quantitative control of the expressed transgene would greatly facilitate studies into neuronal gene function. To develop such a system we incorporated the tetracycline (Tet)-responsive On/Off regulatory elements into type-5 adenoviral (Ad) vectors. Regulation of transgene expression following transfection was measured by placing the enhanced green fluorescent protein (EGFP) gene upstream of the Tet regulatory element. The results showed that cultures of primary hippocampal cells could be transfected with very high efficiency (<70%) by the AdTet-On and AdTet-Off systems. Following transfection with the AdTet-On system no EGFP-fluorescent cells could be detected until doxycycline was added. The AdTet-Off system showed the reverse transcriptional regulation, in that the addition of Tet caused EGFP fluorescence to be abolished.
TRESK (K2P18.1) is a background K+ channel highly expressed in dorsal root and trigeminal ganglia... more TRESK (K2P18.1) is a background K+ channel highly expressed in dorsal root and trigeminal ganglia sensory neurons, where it has been involved in modulating sensory neuron excitability and firing. Reduction in channel expression and function has been reported to enhance nociceptors excitability after injury or inflammation, but its role in somatosensory perception and nociception is still poorly understood. Here we show that TRESK regulates the sensitivity to mechanical and cold stimuli, but it is not involved in the perception of heat. Small/medium-sized DRG sensory neurons from TRESK knockout mice (KO) present an enhanced excitability and recordings from skin nociceptive C-fibers show an increased activation at lower intensity stimulus in response to cold and mechanical stimulation in the absence of the channel. In agreement, mice lacking TRESK present mechanical and cold hypersensitivity compared to wild-type littermates, while heat sensitivity is unaltered. TRESK is also involved...
Cold temperature detection involves the process of sensory transduction in cutaneous primary sens... more Cold temperature detection involves the process of sensory transduction in cutaneous primary sensory nerve terminals, which converts thermal stimuli into depolarizations of the membrane. This transformation into electrical signals is followed by the subsequent propagation of action potentials in cold-sensitive afferent nerve fibers. A large array of ion channels shapes this process; however, the precise contribution of specific ion channel subtypes to cold perception and cold pain remains elusive. This review aims at giving an update on our current understanding of the role played by TRPs, leak K ϩ and voltage-gated Na ϩ and K ϩ channels in the transduction of cold by nociceptors and in cold-induced pain.
Archives internationales de physiologie, de biochimie et de biophysique
Cells expand energy to lower the concentration of free calcium in the cytosol ([Ca2+]i) to a very... more Cells expand energy to lower the concentration of free calcium in the cytosol ([Ca2+]i) to a very low level. Extracellular Ca2+ entering via channels situated in the plasma membrane is expelled into the extracellular medium by a Ca(2+)-Mg(2+)-ATPase or by Na(+)-Ca2+ exchangers. The Ca2+ that enters the cell is sequestered, once inside the cytosol, by a Ca(2+)-Mg(2+)-ATPase, which concentrates Ca2+ in specialized domains of the endoplasmic reticulum. The nucleus and the mitochondria also concentrate Ca2+, but less efficiently. The stimulation of numerous receptors by hormones, growth factors and neurotransmitters coupled to GTP-binding proteins provokes a rapid increase in [Ca2+]i by mobilizing Ca2+ from intra- and extracellular compartments. Membrane coupling is ensured by the activation of a phospholipase C-beta, which hydrolyses a doubly phosphorylated phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). The inositol (1,4,5)-trisphosphate (InsP3) consequently f...
The effects of the beta-adrenoceptor agonist isoprenaline and cyclic AMP (cAMP) on cytosolic free... more The effects of the beta-adrenoceptor agonist isoprenaline and cyclic AMP (cAMP) on cytosolic free Ca2+ ([Ca2+]i) were studied in the single guinea-pig hepatocyte. In common with InsP3-dependent agonists such as noradrenaline or angiotensin II, isoprenaline (0.5-10 microM) and cAMP (50-100 mM, perfused into the cell via the patch-pipette), were able to generate fast and slow fluctuations of [Ca2+]i. Responses to isoprenaline and cAMP also were observed in the absence of external Ca2+. Isoprenaline-evoked [Ca2+]i rises were not blocked by the intracellular perfusion of heparin, suggesting that these fluctuations are independent of the binding of InsP3 to its receptor.
In liver cells, the stimulation of alpha 1-adrenoceptors by noradrenaline induces the production ... more In liver cells, the stimulation of alpha 1-adrenoceptors by noradrenaline induces the production of Ins(1,4,5)P3 through the degradation of membrane polyphosphoinositides [PtdIns(4,5)P2]. InsP3 evokes in turn the release of Ca2+ from internal stores. Our results show that the internal perfusion of single guinea-pig hepatocytes with monoclonal anti-PtdInsP2 antibody blocks the rise in cytosolic free Ca2+ concn. ([Ca2+]i) evoked by noradrenaline, an InsP3-dependent agonist, but not by the monohydroxylated bile acid taurolithocholate 3-sulphate, which is known to permeabilize the endoplasmic reticulum. In these conditions, the bile acid elicited either fast or slow fluctuations of [Ca2+]i independently of any InsP3 production. The responses to the bile acid were also observed in the absence of external Ca2+. The presence of intracellular anti-PtdInsP2 antibody does not affect the response to a photolytic release of InsP3 (1.5 microM final concn.) from a caged precursor.
ABSTRACT Les cellules dépensent de l'énergie pour baisser la concentration du calcium ion... more ABSTRACT Les cellules dépensent de l'énergie pour baisser la concentration du calcium ionisé cytosolique ([Ca2+]i) à un niveau très bas. Le Ca2+ extracellulaire entrant via les canaux localisés dans la membrane plasmique est rejeté vers le milieu extracellulaire par une Ca2+-Mg2+-ATPase, ou des échangeurs Na+/Ca2+. Le Ca2+ entrant est également séquestré depuis le cytosol par une Ca2+-Mg2+-ATPase qui concentre le Ca2+ dans des domaines spécialisés du reticulum endoplasmique. Le noyau et les mitochondries, avec une efficacité moindre, concentrent également le Ca2+. La stimulation de nombreux récepteurs par des hormones, des facteurs de croissance et des neurotrans-metteurs couplés à des protéines liant le GTP, provoquent une augmentation rapide de la [Ca2+]i en mobilisant le Ca2+ depuis les compartiments intra-et extracellulaires. Le couplage membranaire est assuré par l'activation d'une phospholipase C-β qui hydrolyse un phosphoinositide doublement phosphorylé, le phosphatidylinositol 4,5–bisphosphate (PtdIns(4,5)P2). L'inositol (1,4,5)-trisphosphate (InsP3) formé se fixe sur un récepteur composé de quatre monomères homologues de 250 kDa. Le récepteur de l'InsP, a été localisé dans des régions spécialisées, riches en Ca2+, du reticulum endoplasmique. Le récepteur a été purifié et sa séquence obtenue. Réincorporé dans des bicouches planes, il exprime les propriétés d'un canal. Dans la cellule, l'ouverture du canal-récepteur de l'InsP3 provoque la libération du Ca2+ accumulé dans le reticulum endoplasmique. Les analyses cinétiques, effectuées avec des méthodes de mélange et de filtration rapides ou de photolyse d'InsP3 cagé, ont montré que l'InsP3 ouvre le canal avec un délai très court, probablement inférieur à 20 ms. Le récepteur-canal de l'InsP3 présente des propriétés autorégénératives. Avec la stimulation soutenue de l'influx de Ca2+, la libération du Ca2+ entraîne une augmentation de la [Ca2+]i responsable du déclenchement des réponses cellulaires. Les études utilisant des techniques perf ormantes de détection du Ca2+ ionisé cytosolique telles que les protéines bioluminescentes, les indicateurs fluorescents ou les courants ioniques sensibles au Ca2+, ont révélé la complexité des signaux Ca2+ produits par les cellules stimulées. II est apparu que les variations de la [Ca2+]i induites par une stimulation hormonale sont composées d'oscillations dont la fréquence, et non l'amplitude, est dépendante de la concentration de l'hormone. De plus, la numérisation des images enregistrées par caméra vidéo a permis de mettre en évidence les changements de [Ca2+]i au niveau subcellulaire et les vagues Ca2+ dans les cellules stimulées.
In single liver cells, the D-myo-inositol 1,4,5-triphosphate (InsP3)-dependent agonists such as n... more In single liver cells, the D-myo-inositol 1,4,5-triphosphate (InsP3)-dependent agonists such as noradrenaline and angiotensin II evoke oscillations in intracellular calcium [Ca2+]i resulting mostly from the periodic release and reuptake of calcium from intracellular stores. In the present work, we have reexamined the effects of these agonists and investigated whether the natural bile acid taurolithocholic acid 3-sulfate (TLC-S), which permeabilizes the endoplasmic reticulum, could initiate oscillations of [Ca2+]i. Oscillations of [Ca2+]i were monitored with the Ca2(+)-dependent K+ permeability in whole-cell voltage-clamped guinea pig liver cells. Our results confirm the presence of two types of oscillations induced by hormones. They could be distinguished by their frequency periods. The fast (type I) had periods ranging from 5 to 12 s and the slow (type II) from 60 to 240 s. They have been respectively attributed to second messenger- and receptor-controlled oscillations, respectively. Our results also show that TLC-S, as noradrenaline and angiotensin II, induced the activation of this Ca(+)-dependent K+ current and was able to reproduce both types of oscillations. The bile acid effect was not blocked by intracellular perfusion of heparin known to inhibit both InsP3 binding and InsP3-evoked Ca2+ release in several tissues. In these conditions, TLC-S only evoked type I oscillations, suggesting that these fluctuations could originate from a mechanism that is independent of InsP3 and is an intrinsic property of internal Ca2+ stores.
Implication des canaux ioniques dans l'hypersensibilité au froid induite par l'oxaliplatine Oxali... more Implication des canaux ioniques dans l'hypersensibilité au froid induite par l'oxaliplatine Oxaliplatin-induced cold hypersensitivity is due to remodeling of ion channels in nociceptors
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