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Accueil > Agenda > Les séminaires Jean Roche > Physiologie et pathologie des canaux ioniques des axones myélinisés.

Physiologie et pathologie des canaux ioniques des (...)

Lundi 13 février 2006,11h, salle Lissitzky.


1 : Rev Neurol (Paris). 2004 May ;160(5 Pt 2):S16-27.

[Ion channels and demyelination : basis of a treatment of experimental autoimmune encephalomyelitis (EAE) by potassium channel blockers]

Devaux J, Beeton C, Beraud E, Crest M.

Laboratoire Integration des Informations Sensorielles, CNRS UMR 6150, Universite de la Mediterranee, Faculte de Medecine, IFR Jean Roche, Bd Pierre Dramard, 13916, Marseille, France.

Voltage-gated potassium channels (Kv channels) are ion channels, openings of which provide an outward flow of potassium ions repolarising the cell. In neurons, Kv channels play a crucial role in action potential repolarisation and in shaping neuronal excitability. In non-excitable cells, such as T lymphocytes, Kv channels and calcium-activated K+ channels (KCa channels) determine the driving force for Ca2+ entry. During T cell activation the calcium entry depolarises the cell and increases the cytosolic calcium concentration, which in return activates Kv and KCa channels. K+ channel opening repolarises the cell and drives the membrane potential to a negative voltage. The roles of Kv channels in nervous and immune systems have been investigated here by means of a rat experimental autoimmune disease of the central nervous system, the experimental autoimmune encephalomyelitis (EAE). EAE is characterised clinically by paralysis, and pathologically by inflammatory cell infiltrations into the brain and the spinal cord. Among the inflammatory cells, T lymphocytes play a major role. Hence, EAE can be adoptively transferred into syngenic animals by the injection of T cells reactive to myelin antigens. During adoptive-EAE, somato-sensory evoked potentials recorded along the spinal tracts decrease in amplitude and axonal propagation is disrupted. We have analysed the consequences of Kv channels blockade by peptidyl toxins on central nerve conduction, on T cell activation and on the time course of EAE. In rat optic nerves, Kv channels have been identified up from postnatal day 1. Their blockade by kaliotoxin (a scorpion toxin) or by dendrotoxin-I (a snake toxin) enlarges the compound action potentials, demonstrating the participation of Kv channels to spike repolarisation. This effect disappears at adult age due to the sequestration of Kv channels under the myelin, in the paranodal regions. During acute demyelination by lysophosphatidyl-choline, the surface area of compound action potential decreased probably because conduction block occurred. Demyelination unmasked Kv channels, which are again accessible to toxins. Their blockade by dendrotoxin-I or kaliotoxin favoured a slow delayed conduction suggesting that those Kv channel blockers exert a neurological benefit during demyelinating diseases. In a T-cell line reactive to myelin basic protein antigen, which is used to adoptively transfer experimental autoimmune encephalomyelitis, Kv1.3 channels are constitutively expressed. Their blockade leads to a pronounced reduction of the T cell proliferative response, cytokine production and Ca2+ influx. In the rat, blockade of Kv1.3 inhibits the delayed type hypersensitivity response to myelin basic protein prevents and treats adoptive experimental autoimmune encephalomyelitis. Blockade of Kv channels alone or in combination with KCa channels improves the symptoms of the disease. These results demonstrate that K+ channel blockers displaying high selectivity are potent immunosuppressive agents with beneficial symptomatic effects in experimental autoimmune encephalomyelitis.

2 : J Neurosci. 2003 Jun 1 ;23(11):4509-18.

Kv3.1b is a novel component of CNS nodes.

Devaux J, Alcaraz G, Grinspan J, Bennett V, Joho R, Crest M, Scherer SS.

Department of Neurology, The University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104-6077, USA. jdevaux

We herein demonstrate that Kv3.1b subunits are present at nodes of Ranvier in the CNS of both rats and mice. Kv3.1b colocalizes with voltage-gated Na+ channels in a subset of nodes in the spinal cord, particularly those of large myelinated axons. Kv3.1b is abundantly expressed in the gray matter of the spinal cord, but does not colocalize with Na+ channels in initial segments. In the PNS, few nodes are Kv3.1b-positive. During the development of the CNS, Kv3.1b clustering at nodes occurs later than that of Na+ channels, but precedes the juxtaparanodal clustering of Kv1.2. Moreover, in myelin-deficient rats, which have severe CNS dysmyelination, node-like clusters of Kv3.1b and Na+ channels are observed even in regions devoid of oligodendrocytes. Ankyrin G coimmunoprecipitates Kv3.1b in vivo, indicating that these two proteins may interact in the CNS at nodes. 4-Aminopyridine, a K+ channel blocker, broadened the compound action potential recorded from adult rat optic nerve and spinal cord, but not from the sciatic nerve. These effects were also observed in Kv3.1-deficient mice. In conclusion, Kv3.1b is the first K+ channel subunit to be identified in CNS nodes ; but Kv3.1b does not account for the effects of 4-aminopyridine on central myelinated tracts.

3 : Neuroreport. 2003 Mar 3 ;14(3):317-20.

Myelin basic protein-reactive T cells induce conduction failure in vivo but not in vitro.

Devaux J, Forni C, Beeton C, Barbaria J, Beraud E, Gola M, Crest M.

Laboratoire de Neurobiologie Cellulaire et Fonctionnelle, FRE 2131, CNRS, 31, Chemin Joseph-Aiguier, 13402 Marseille Cedex 20, France.

The ability of myelin basic protein (MBP)-reactive T cells to induce conduction failure was investigated and. With the model, somatosensory evoked potentials (SEP) were recorded before and during adoptively transferred experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Maximum amplitude SEP were reached within 15 min of anesthesia. During EAE, the SEP decreased considerably and their onset was delayed. However, the compound action potentials (CAPs) recorded from Lewis rat optic nerves incubated with encephalitogenic T cells were not affected, emphasizing the importance of environmental factors. This study shows that the model described here is an useful means of investigating the neurological disorders associated with EAE.

4 : J Neurophysiol. 2002 Mar ;87(3):1376-85.

Effects of K+ channel blockers on developing rat myelinated CNS axons : identification of four types of K+ channels.

Devaux J, Gola M, Jacquet G, Crest M.

Laboratoire Integration des Informations Sensorielles, Centre National de la Recherche Scientifique, 31 Chemin Joseph-Aiguier, 13402 Marseille Cedex 20, France.

Four blockers of voltage-gated potassium channels (Kv channels) were tested on the compound action potentials (CAPs) of rat optic nerves in an attempt to determine the regulation of Kv channel expression during the process of myelination. Before myelination occurred, 4-aminopyridine (4-AP) increased the amplitude, duration, and refractory period of the CAPs. On the basis of their pharmacological sensitivity, 4-AP-sensitive channels were divided in two groups, the one sensitive to kaliotoxin (KTX), dendrotoxin-I (DTX-I), and 4-AP, and the other sensitive only to 4-AP. In addition, tetraethylammonium chloride (TEA) applied alone broadened the CAPs. At the onset of myelination, DTX-I induced a more pronounced effect than KTX ; this indicates that a fourth group of channels sensitive to 4-AP and DTX-I but insensitive to KTX had developed. The effects of KTX and DTX-I gradually disappeared during the period of myelination. Electron microscope findings showed that the disappearance of these effects was correlated with the ongoing process of myelination. This was confirmed by the fact that DTX-I and KTX enlarged the CAPs of demyelinated adult optic nerves. These results show that KTX- and DTX-sensitive channels are sequestrated in paranodal regions. During the process of myelination, KTX had less pronounced effects than DTX-I on demyelinated nerves, which suggests that the density of the KTX-sensitive channels decreased during this process. By contrast, 4-AP increased the amplitude, duration, and refractory period of the CAPs at all the ages tested and to a greater extent than KTX and DTX-I. The effects of TEA alone also gradually disappeared during this period. However, effects of TEA on CAPs were observed when this substance was applied after 4-AP to the adult optic nerve ; this shows that TEA-sensitive channels are not masked by the myelin sheath. In conclusion, the process of myelination seems to play an important part in the regulation and setting of Kv channels in optic nerve axons.

5 : J Immunol. 2001 Jan 15 ;166(2):936-44.

Selective blocking of voltage-gated K+ channels improves experimental autoimmune encephalomyelitis and inhibits T cell activation.

Beeton C, Barbaria J, Giraud P, Devaux J, Benoliel AM, Gola M, Sabatier JM, Bernard D, Crest M, Beraud E.

Laboratoire d’Immunologie, Faculte de Medecine, Universite de la Mediterranee, Unite de Formation et de Recherche de Medecine, Universite de la Mediterranee, 13385 Marseille Cedex 5, France.

Kaliotoxin (KTX), a blocker of voltage-gated potassium channels (Kv), is highly selective for Kv1.1 and Kv1.3. First, Kv1.3 is expressed by T lymphocytes. Blockers of Kv1.3 inhibit T lymphocyte activation. Second, Kv1.1 is found in paranodal regions of axons in the central nervous system. Kv blockers improve the impaired neuronal conduction of demyelinated axons in vitro and potentiate the synaptic transmission. Therefore, we investigated the therapeutic properties of KTX via its immunosuppressive and symptomatic neurological effects, using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. The T line cells used to induce adoptive EAE were myelin basic protein (MBP)-specific, constitutively contained mRNA for Kv1.3. and expressed Kv1.3. These channels were shown to be blocked by KTX. Activation is a crucial step for MBP T cells to become encephalitogenic. The addition of KTX during Ag-T cell activation led to a great reduction in the MBP T cell proliferative response, in the production of IL-2 and TNF, and in Ca(2+) influx. Furthermore, the addition of KTX during T cell activation in vitro led a decreased encephalitogenicity of MBP T cells. Moreover, KTX injected into Lewis rats impaired T cell function such as the delayed-type hypersensitivity. Lastly, the administration of this blocker of neuronal and lymphocyte channels to Lewis rats improved the symptoms of EAE. We conclude that KTX is a potent immunosuppressive agent with beneficial effects on the neurological symptoms of EAE.

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