Patrick Meuth

Publications of Patrick Meuth

• Differential regulation of HCN channel isoform expression in thalamic neurons of epileptic and non-epileptic rat strains.

  Authors: Tatyana Kanyshkova, Patrick Meuth, Pawan Bista, Zhiqiang Liu, Petra Ehling, Luigi Caputi, Michael Doengi, Dane M Chetkovich, Hans-Christian Pape, Thomas Budde

  Neurobiology of disease. 09/2011; 45(1):450-61.

  Hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels represent the molecular substrate of the hyperpolarization-activated inward current (I(h)). Although these channels act asHyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels represent the molecular substrate of the hyperpolarization-activated inward current (I(h)). Although these channels act as pacemakers for the generation of rhythmic activity in the thalamocortical network during sleep and epilepsy, their developmental profile in the thalamus is not yet fully understood. Here we combined electrophysiological, immunohistochemical, and mathematical modeling techniques to examine HCN gene expression and I(h) properties in thalamocortical relay (TC) neurons of the dorsal part of the lateral geniculate nucleus (dLGN) in an epileptic (WAG/Rij) compared to a non-epileptic (ACI) rat strain. Recordings of TC neurons between postnatal day (P) 7 and P90 in both rat strains revealed that I(h) was characterized by higher current density, more hyperpolarized voltage dependence, faster activation kinetics, and reduced cAMP-sensitivity in epileptic animals. All four HCN channel isoforms (HCN1-4) were detected in dLGN, and quantitative analyses revealed a developmental increase of protein expression of HCN1, HCN2, and HCN4 but a decrease of HCN3. HCN1 was expressed at higher levels in WAG/Rij rats, a finding that was correlated with increased expression of the interacting proteins filamin A (FilA) and tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b). Analysis of a simplified computer model of the thalamic network revealed that the alterations of I(h) found in WAG/Rij rats compensate each other in a way that leaves I(h) availability constant, an effect that ensures unaltered cellular burst activity and thalamic oscillations. These data indicate that during postnatal developmental the hyperpolarizing shift in voltage dependency (resulting in less current availability) is compensated by an increase in current density in WAG/Rij thereby possibly limiting the impact of I(h) on epileptogenesis. Because HCN3 is expressed higher in young versus older animals, HCN3 likely does not contribute to alterations in I(h) in older animals.

• Volume regulation of murine T lymphocytes relies on voltage-dependent and two-pore domain potassium channels.

  Authors: Nicole Bobak, Stefan Bittner, Joseph Andronic, Susanne Hartmann, Friederike Mühlpfordt, Tilman Schneider-Hohendorf, Karen Wolf, Carsten Schmelter, Kerstin Göbel, Patrick Meuth, Heiko Zimmermann, Frank Döring, Erhard Wischmeyer, Thomas Budde, Heinz Wiendl, Sven G Meuth, Vladimir L Sukhorukov

  Biochimica et biophysica acta. 08/2011; 1808(8):2036-44.

  A variety of ion channels are supposed to orchestrate the homoeostatic volume regulation in T lymphocytes. However, the relative contribution of different potassium channels to the osmotic volumeA variety of ion channels are supposed to orchestrate the homoeostatic volume regulation in T lymphocytes. However, the relative contribution of different potassium channels to the osmotic volume regulation and in particular to the regulatory volume decrease (RVD) in T cells is far from clear. This study explores a putative role of the newly identified K(2P) channels (TASK1, TASK2, TASK3 and TRESK) along with the voltage-gated potassium channel K(V)1.3 and the calcium-activated potassium channel K(Ca)3.1 in the RVD of murine T lymphocytes, using genetic and pharmacological approaches. K(2P) channel knockouts exerted profound effects on the osmotic properties of murine T lymphocytes, as revealed by reduced water and RVD-related solute permeabilities. Moreover, both genetic and pharmacological data proved a key role of K(V)1.3 and TASK2 channels in the RVD of murine T cells exposed to hypotonic saline. Our experiments demonstrate a leading role of potassium channels in the osmoregulation of T lymphocytes under different conditions. In summary, the present study sheds new light on the complex and partially redundant network of potassium channels involved in the basic physiological process of the cellular volume homeostasis and extends the repertoire of potassium channels by the family of K(2P) channels.

• Glatiramer acetate attenuates pro-inflammatory T cell responses but does not directly protect neurons from inflammatory cell death.

  Authors: Alexander M Herrmann, Kerstin Göbel, Ole J Simon, Nico Melzer, Michael K Schuhmann, Max-Philipp Stenner, Andreas Weishaupt, Christoph Kleinschnitz, Stefan Bittner, Patrick Meuth, Olaf Stuve, Thomas Budde, Bernd C Kieseier, Heinz Wiendl, Sven G Meuth

  The American journal of pathology. 10/2010; 177(6):3051-60.

  Glatiramer acetate (GA) is a synthetic, random, basic copolymer capable of modulating adaptive T cell responses. In animal models of various inflammatory and degenerative central nervous systemGlatiramer acetate (GA) is a synthetic, random, basic copolymer capable of modulating adaptive T cell responses. In animal models of various inflammatory and degenerative central nervous system disorders, GA-induced T cells cross the blood-brain barrier, secrete high levels of anti-inflammatory cytokines and neurotrophins, and thus both reduce neuronal damage and promote neurogenesis. Recently, it has been suggested that GA itself may permeate the (impaired) blood-brain-barrier and directly protect neurons under conditions of inflammation-mediated neurodegeneration. To test this hypothesis, we examined the direct effects of GA on neuronal functionality and T cell-mediated neuronal apoptosis in culture, acute brain slices, and focal experimental autoimmune encephalomyelitis. GA caused a depolarization of the resting membrane potential and led to an immediate impairment of action potential generation in neurons. Moreover, GA-incubated neurons underwent dose-dependent apoptosis. Apoptosis of ovalbumin peptide-loaded major histocompatibility complex class I-expressing neurons induced by ovalbumin-specific effector T cells could be reduced by pre-incubation of T cells, but not neurons with GA. Similar results could be found using acute brain slices. In focal experimental autoimmune encephalomyelitis, lesion size and neuronal apoptosis could be limited by pretreating rats with GA, whereas intracerebral GA application into the inflammatory lesion had no effect on neuronal survival. Our data suggest that GA attenuates adaptive pro-inflammatory T cell responses, but does not exert direct neuroprotective effects.

• Upregulation of K2P5.1 potassium channels in multiple sclerosis.

  Authors: Stefan Bittner, Nicole Bobak, Alexander M Herrmann, Kerstin Göbel, Patrick Meuth, Karin G Höhn, Max-Philipp Stenner, Thomas Budde, Heinz Wiendl, Sven G Meuth

  Annals of neurology. 07/2010; 68(1):58-69.

  Activation of T cells critically depends on potassium channels. We here characterize the impact of K(2P)5.1 (KCNK5; TASK2), a member of the 2-pore domain family of potassium channels, on T-cellActivation of T cells critically depends on potassium channels. We here characterize the impact of K(2P)5.1 (KCNK5; TASK2), a member of the 2-pore domain family of potassium channels, on T-cell function and demonstrate its putative relevance in a T-cell-mediated autoimmune disorder, multiple sclerosis (MS). Expression of K(2P)5.1 was investigated on RNA and protein level in different immune cells and in MS patients' biospecimens (peripheral blood mononuclear cells, cerebrospinal fluid cells, brain tissue specimen). Functional consequences of K(2P)5.1 expression were analyzed using pharmacological modulation, small interfering RNA (siRNA), overexpression, electrophysiological recordings, and computer modeling. Human T cells constitutively express K(2P)5.1. After T-cell activation, a significant and time-dependent upregulation of K(2P)5.1 channel expression was observed. Pharmacological blockade of K(2P)5.1 or knockdown with siRNA resulted in reduced T-cell functions, whereas overexpression of K(2P)5.1 had the opposite effect. Electrophysiological recordings of T cells clearly dissected K(2P)5.1-mediated effects from other potassium channels. The pathophysiological relevance of these findings was demonstrated by a significant K(2P)5.1 upregulation in CD4(+) and CD8(+) T cells in relapsing/remitting MS (RRMS) patients during acute relapses as well as higher levels on CD8(+) T cells of clinically isolated syndrome, RRMS, and secondary progressive multiple sclerosis patients during clinically stable disease. T cells in the cerebrospinal fluid from MS patients exhibit significantly elevated K(2P)5.1 levels. Furthermore, K(2P)5.1-positive T cells can be found in inflammatory lesions in MS tissue specimens. Selective targeting of K(2P)5.1 may hold therapeutic promise for MS and putatively other T-cell-mediated disorders.

• Cytotoxic CD8+ T cell-neuron interactions: perforin-dependent electrical silencing precedes but is not causally linked to neuronal cell death.

  Authors: Sven G Meuth, Alexander M Herrmann, Ole J Simon, Volker Siffrin, Nico Melzer, Stefan Bittner, Patrick Meuth, Harald F Langer, Stefan Hallermann, Nadia Boldakowa, Josephine Herz, Thomas Munsch, Peter Landgraf, Orhan Aktas, Manfred Heckmann, Volkmar Lessmann, Thomas Budde, Bernd C Kieseier, Frauke Zipp, Heinz Wiendl

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 12/2009; 29(49):15397-409.

  Cytotoxic CD8(+) T cells are considered important effector cells contributing to neuronal damage in inflammatory and degenerative CNS disorders. Using time-lapse video microscopy and two-photonCytotoxic CD8(+) T cells are considered important effector cells contributing to neuronal damage in inflammatory and degenerative CNS disorders. Using time-lapse video microscopy and two-photon imaging in combination with whole-cell patch-clamp recordings, we here show that major histocompatibility class I (MHC I)-restricted neuronal antigen presentation and T cell receptor specificity determine CD8(+) T-cell locomotion and neuronal damage in culture and hippocampal brain slices. Two separate functional consequences result from a direct cell-cell contact between antigen-presenting neurons and antigen-specific CD8(+) T cells. (1) An immediate impairment of electrical signaling in single neurons and neuronal networks occurs as a result of massive shunting of the membrane capacitance after insertion of channel-forming perforin (and probably activation of other transmembrane conductances), which is paralleled by an increase of intracellular Ca(2+) levels (within <10 min). (2) Antigen-dependent neuronal apoptosis may occur independently of perforin and members of the granzyme B cluster (within approximately 1 h), suggesting that extracellular effects can substitute for intracellular delivery of granzymes by perforin. Thus, electrical silencing is an immediate consequence of MHC I-restricted interaction of CD8(+) T cells with neurons. This mechanism is clearly perforin-dependent and precedes, but is not causally linked, to neuronal cell death.

• Burst discharges in neurons of the thalamic reticular nucleus are shaped by calcium-induced calcium release.

  Authors: Philippe Coulon, David Herr, Tatyana Kanyshkova, Patrick Meuth, Thomas Budde, Hans-Christian Pape

  Cell calcium. 11/2009;

  The nucleus reticularis thalami (NRT) is a layer of inhibitory neurons that surrounds the dorsal thalamus. It appears to be the 'pacemaker' of certain forms of slow oscillations in the thalamus andThe nucleus reticularis thalami (NRT) is a layer of inhibitory neurons that surrounds the dorsal thalamus. It appears to be the 'pacemaker' of certain forms of slow oscillations in the thalamus and was proposed to be a key determinant of the internal attentional searchlight as well as the origin of hypersynchronous activity during absence seizures. Neurons of the NRT exhibit a transient depolarization termed low threshold spike (LTS) following sustained hyperpolarization. This is caused by the activation of low-voltage-activated Ca(2+) channels (LVACC). Although the role of these channels in thalamocortical oscillations was studied in great detail, little is known about the downstream intracellular Ca(2+) signalling pathways and their feedback onto the oscillations. A signalling triad consisting of the sarco(endo)plasmic reticulum calcium ATPase (SERCA), Ca(2+) activated K(+) channels (SK2), and LVACC is active in dendrites of NRT neurons and shapes rhythmic oscillations. The aim of our study was to find out (i) if and how Ca(2+)-induced Ca(2+) release (CICR) via ryanodine receptors (RyR) can be evoked in NRT neurons and (ii) how the released Ca(2+) affects burst activity. Combining electrophysiological, immunohistochemical, and two-photon Ca(2+) imaging techniques, we show that CICR in NRT neurons takes place by a cell-type specific coupling of LVACC and RyR. CICR could be evoked by the application of caffeine, by activation of LVACC, or by repetitive LTS generation. During the latter, CICR contributed approximately 30% to the resulting build-up of [Ca(2+)](i). CICR was abolished by cyclopiazonic acid, a specific blocker for SERCA, or by high concentrations of ryanodine (50muM). Unlike other thalamic nuclei, in the NRT the activation of high-voltage-activated Ca(2+) channels failed to evoke CICR. While action potentials contributed little to the build-up of [Ca(2+)](i) upon repetitive LTS generation, the Ca(2+) released via RyR significantly reduced the number of action potentials during an LTS and reduced the neurons' low threshold activity, thus potentially reducing hypersynchronicity. This effect persisted in the presence of the SK2 channel blocker apamin. We conclude that the activation of LVACC specifically causes CICR via RyR in neurons of the NRT, thereby adding a Ca(2+)-dependent intracellular route to the mechanisms determining rhythmic oscillatory bursting in this nucleus.

• Postnatal expression pattern of HCN channel isoforms in thalamic neurons: relationship to maturation of thalamocortical oscillations.

  Authors: Tatyana Kanyshkova, Matthias Pawlowski, Patrick Meuth, Celine Dubé, Roland A Bender, Amy L Brewster, Arnd Baumann, Tallie Z Baram, Hans-Christian Pape, Thomas Budde

  The Journal of neuroscience : the official journal of the Society for Neuroscience. 08/2009; 29(27):8847-57.

  Hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels are the molecular substrate of the hyperpolarization-activated inward current (I(h)). Because the developmental profile ofHyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels are the molecular substrate of the hyperpolarization-activated inward current (I(h)). Because the developmental profile of HCN channels in the thalamus is not well understood, we combined electrophysiological, molecular, immunohistochemical, EEG recordings in vivo, and computer modeling techniques to examine HCN gene expression and I(h) properties in rat thalamocortical relay (TC) neurons in the dorsal part of the lateral geniculate nucleus and the functional consequence of this maturation. Recordings of TC neurons revealed an approximate sixfold increase in I(h) density between postnatal day 3 (P3) and P106, which was accompanied by significantly altered current kinetics, cAMP sensitivity, and steady-state activation properties. Quantification on tissue levels revealed a significant developmental decrease in cAMP. Consequently the block of basal adenylyl cyclase activity was accompanied by a hyperpolarizing shift of the I(h) activation curve in young but not adult rats. Quantitative analyses of HCN channel isoforms revealed a steady increase of mRNA and protein expression levels of HCN1, HCN2, and HCN4 with reduced relative abundance of HCN4. Computer modeling in a simplified thalamic network indicated that the occurrence of rhythmic delta activity, which was present in the EEG at P12, differentially depended on I(h) conductance and modulation by cAMP at different developmental states. These data indicate that the developmental increase in I(h) density results from increased expression of three HCN channel isoforms and that isoform composition and intracellular cAMP levels interact in determining I(h) properties to enable progressive maturation of rhythmic slow-wave sleep activity patterns.

• Correlation of T-channel coding gene expression, I(T), and the low threshold Ca(2+) spike in the thalamus of a rat model of absence epilepsy.

  Authors: Tilman Broicher, Tatyana Kanyshkova, Patrick Meuth, Hans-Christian Pape, Thomas Budde

  Molecular and cellular neurosciences. 08/2008;

  T-type Ca(2+) current-dependent burst firing of thalamic neurons is thought to be involved in the hyper-synchronous activity observed during absence seizures. Here we investigate the correlationT-type Ca(2+) current-dependent burst firing of thalamic neurons is thought to be involved in the hyper-synchronous activity observed during absence seizures. Here we investigate the correlation between the expression of T-channel coding genes (alpha1G, -H, -I), T-type Ca(2+) current, and the T-current-dependent low threshold Ca(2+) spike in three functionally distinct thalamic nuclei (lateral geniculate nucleus; centrolateral nucleus; reticular nucleus) in a rat model of absence epilepsy, the WAG/Rij rats, and a non-epileptic control strain, the ACI rats. The lateral geniculate nucleus and centrolateral nucleus were found to primarily express alpha1G and alpha1I, while the reticular thalamic nucleus expressed alpha1H and alpha1I. Expression was higher in WAG/Rij when compared to ACI. The T-type Ca(2+) current properties matched the predictions derived from the expression pattern analysis. Current density was larger in all nuclei of WAG/Rij rats when compared to ACI and correlated with LTS size and the minimum LTS generating slope, while T-type Ca(2+) current voltage dependency correlated with the LTS onset potential.

• TWIK-related acid-sensitive K+ channel 1 (TASK1) and TASK3 critically influence T lymphocyte effector functions.

  Authors: Sven G Meuth, Stefan Bittner, Patrick Meuth, Ole J Simon, Thomas Budde, Heinz Wiendl

  The Journal of biological chemistry. 06/2008; 283(21):14559-70.

  Two major K(+) channels are expressed in T cells, (i) the voltage-dependent K(V)1.3 channel and (ii) the Ca(2+)-activated K(+) channel KCa 3.1 (IKCa channel). Both critically influence T cellTwo major K(+) channels are expressed in T cells, (i) the voltage-dependent K(V)1.3 channel and (ii) the Ca(2+)-activated K(+) channel KCa 3.1 (IKCa channel). Both critically influence T cell effector functions in vitro and animal models in vivo. Here we identify and characterize TWIK-related acid-sensitive potassium channel 1 (TASK1) and TASK3 as an important third K(+) conductance on T lymphocytes. T lymphocytes constitutively express TASK1 and -3 protein. Application of semi-selective TASK blockers resulted in a significant reduction of cytokine production and cell proliferation. Interference with TASK channels on CD3(+) T cells revealed a dose-dependent reduction ( approximately 40%) of an outward current in patch clamp recordings indicative of TASK channels, a finding confirmed by computational modeling. In vivo relevance of our findings was addressed in an experimental model of multiple sclerosis, adoptive transfer experimental autoimmune encephalomyelitis. Pretreatment of myelin basic protein-specific encephalitogenic T lymphocytes with TASK modulators was associated with significant amelioration of the disease course in Lewis rats. These data introduce K(2)P channels as novel potassium conductance on T lymphocytes critically influencing T cell effector function and identify a possible molecular target for immunomodulation in T cell-mediated autoimmune disorders.

• Reciprocal modulation of I (h) and I (TASK) in thalamocortical relay neurons by halothane.

  Authors: Thomas Budde, Philippe Coulon, Matthias Pawlowski, Patrick Meuth, Tatyana Kanyshkova, Ansgar Japes, Sven Meuth, Hans-Christian Pape

  Pflugers Archiv : European journal of physiology. 06/2008;

  By combining electrophysiological, immunohistochemical, and computer modeling techniques, we examined the effects of halothane on the standing outward current (I (SO)) and theBy combining electrophysiological, immunohistochemical, and computer modeling techniques, we examined the effects of halothane on the standing outward current (I (SO)) and the hyperpolarization-activated current (I (h)) in rat thalamocortical relay (TC) neurons of the dorsal lateral geniculate nucleus (dLGN). Hyperpolarizing voltage steps elicited an instantaneous current component (I (i)) followed by a slower time-dependent current that represented I (h). Halothane reduced I (h) by shifting the voltage dependency of activation toward more negative potentials and by reducing the maximal conductance. Moreover, halothane augmented I (i) and I (SO). During the blockade of I (h) through Cs(+), the current-voltage relationship of the halothane-sensitive current closely resembled the properties of a current through members of the TWIK-related acid-sensitive K(+) (TASK) channel family (I (TASK)). Computer simulations in a single-compartment TC neuron model demonstrated that the modulation of I (h) and I (TASK) is sufficient to explain the halothane-induced hyperpolarization of the membrane potential observed in current clamp recordings. Immunohistochemical staining revealed protein expression of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel proteins HCN1, HCN2, and HCN4. Together with the dual effect of halothane on I (h) properties, these results suggest that I (h) in TC neurons critically depends on HCN1/HCN2 heterodimers. It is concluded that the reciprocal modulation of I (h) and I (TASK) is an important mechanism of halothane action in the thalamus.

• Specific expression of low-voltage-activated calcium channel isoforms and splice variants in thalamic local circuit interneurons.

  Authors: Tilman Broicher, Tatyana Kanyshkova, Peter Landgraf, Vladan Rankovic, Patrick Meuth, Sven G Meuth, Hans-Christian Pape, Thomas Budde

  Molecular and cellular neurosciences. 11/2007; 36(2):132-45.

  It has been suggested that the specific burst firing patterns of thalamic neurons reflect differential expression of low-voltage-activated (LVA) Ca(2+) channel subtypes and their splice variants. ByIt has been suggested that the specific burst firing patterns of thalamic neurons reflect differential expression of low-voltage-activated (LVA) Ca(2+) channel subtypes and their splice variants. By combining electrophysiological, molecular biological, immunological, and computational modeling techniques we here show that diverging LVA Ca(2+) currents of thalamocortical relay (TC) and GABAergic interneurons of the dLGN correlate with a differential expression of LVA Ca(2+) channel splice variations and isoforms (alpha1G-a in TC; alpha1G-bc and alpha1I in interneurons). Implementation of the observed LVA Ca(2+) current differences into a TC neuron model changed the burst firing from TC-like to interneuron-like. We conclude that alternative splicing of the alpha1G isoform in dLGN TC and interneurons, and the exclusive expression of the alpha1I isoform in interneurons play a prominent role in setting the different LVA Ca(2+) current properties of TC and interneurons, which critically contribute to the diverging burst firing behavior of these neurons.

• T-current related effects of antiepileptic drugs and a Ca2+ channel antagonist on thalamic relay and local circuit interneurons in a rat model of absence epilepsy.

  Authors: Tilman Broicher, Thomas Seidenbecher, Patrick Meuth, Thomas Munsch, Sven G Meuth, Tatyana Kanyshkova, Hans-Christian Pape, Thomas Budde

  Neuropharmacology. 09/2007; 53(3):431-46.

  Channel blocking, anti-oscillatory, and anti-epileptic effects of clinically used anti-absence substances (ethosuximide, valproate) and the T-type Ca2+ current (IT) blocker mibefradil were tested byChannel blocking, anti-oscillatory, and anti-epileptic effects of clinically used anti-absence substances (ethosuximide, valproate) and the T-type Ca2+ current (IT) blocker mibefradil were tested by analyzing membrane currents in acutely isolated local circuit interneurons and thalamocortical relay (TC) neurons, slow intrathalamic oscillations in brain slices, and spike and wave discharges (SWDs) occurring in vivo in Wistar Albino Glaxo rats from Rijswijk (WAG/Rij). Substance effects in vitro were compared between WAG/Rij and a non-epileptic control strain, the ACI rats. Ethosuximide (ETX) and valproate were found to block IT in acutely isolated thalamic neurons. Block of IT by therapeutically relevant ETX concentrations (0.25-0.75 mM) was stronger in WAG/Rij, although the maximal effect at saturating concentrations (>or=10 mM) was stronger in ACI. Ethosuximide delayed the onset of the low threshold Ca2+ spike (LTS) of neurons recorded in slice preparations. Mibefradil (>or=2 microM) completely blocked IT and the LTS, dampened evoked thalamic oscillations, and attenuated SWDs in vivo. Computational modeling demonstrated that the complete effect of ETX can be replicated by a sole reduction of IT. However, the necessary degree of IT reduction was not induced by therapeutically relevant ETX concentrations. A combined reduction of IT, the persistent sodium current, and the Ca2+ activated K+ current resulted in an LTS alteration resembling the experimental observations. In summary, these results support the hypothesis of IT reduction as part of the mechanism of action of anti-absence drugs and demonstrate the ability of a specific IT antagonist to attenuate rhythmic burst firing and SWDs.

• Membrane resting potential of thalamocortical relay neurons is shaped by the interaction among TASK3 and HCN2 channels.

  Authors: Sven G Meuth, Tatyana Kanyshkova, Patrick Meuth, Peter Landgraf, Thomas Munsch, Andreas Ludwig, Franz Hofmann, Hans-Christian Pape, Thomas Budde

  Journal of neurophysiology. 10/2006; 96(3):1517-29.

  By combining molecular biological, electrophysiological, immunological, and computer modeling techniques, we here demonstrate a counterbalancing contribution of TASK channels, underlyingBy combining molecular biological, electrophysiological, immunological, and computer modeling techniques, we here demonstrate a counterbalancing contribution of TASK channels, underlying hyperpolarizing K+ leak currents, and HCN channels, underlying depolarizing Ih, to the resting membrane potential of thalamocortical relay (TC) neurons. RT-PCR experiments revealed the expression of TASK1, TASK3, and HCN1-4. Quantitative determination of mRNA expression levels and immunocytochemical staining demonstrated that TASK3 and HCN2 channels represent the dominant thalamic isoforms and are coexpressed in TC neurons. Extracellular acidification, a standard procedure to inhibit TASK channels, blocked a TASK current masked by additional action on HCN channels. Only in the presence of the HCN blocker ZD7288 was the pH-sensitive component typical for a TASK current, i.e., outward rectification and current reversal at the K+ equilibrium potential. In a similar way extracellular acidification was able to shift the activity pattern of TC neurons from burst to tonic firing only during block of Ih or genetic knock out of HCN channels. A single compartmental computer model of TC neurons simulated the counterbalancing influence of TASK and HCN on the resting membrane potential. It is concluded that TASK3 and HCN2 channels stabilize the membrane potential by a mutual functional interaction, that the most efficient way to regulate the membrane potential of TC neurons is the converse modulation of TASK and HCN channels, and that TC neurons are potentially more resistant to insults accompanied by extracellular pH shifts in comparison to other CNS regions.

• The contribution of TWIK-related acid-sensitive K+-containing channels to the function of dorsal lateral geniculate thalamocortical relay neurons.

  Authors: Sven G Meuth, M Isabel Aller, Thomas Munsch, Thekla Schuhmacher, Thomas Seidenbecher, Patrick Meuth, Christoph Kleinschnitz, Hans-Christian Pape, Heinz Wiendl, William Wisden, Thomas Budde

  Molecular pharmacology. 05/2006; 69(4):1468-76.

  A genetic knockout was used to determine the specific contribution of TWIK-related acid-sensitive K+ (TASK)-1 channels to the function of dorsal lateral geniculate nucleus (DLG) thalamocortical relayA genetic knockout was used to determine the specific contribution of TWIK-related acid-sensitive K+ (TASK)-1 channels to the function of dorsal lateral geniculate nucleus (DLG) thalamocortical relay (TC) neurons. Disruption of TASK-1 function produced an approximately 19% decrease in amplitude of the standing outward current (ISO) and a 3 +/- 1-mV depolarizing shift in resting membrane potential (Vrest) of DLG neurons. We estimated that current through TASK-1 homodimers or TASK-1/TASK-3 heterodimers contribute(s) approximately one third of the current sensitive to TASK channel modulators in DLG TC neurons. The effects of the TASK channel blocker bupivacaine (20 microM), of muscarine (50 microM), and of H+ on ISO were reduced to approximately 60%, 59%, and shifted to more acidic pH values, respectively. The blocking effect of anandamide on ISO [30 microM; 23 +/- 3% current decrease in wild type (WT)] was absent in TASK-1 knockout (TASK-1-/-) mice (9 +/- 6% current increase). Comparable results were obtained with the more stable anand-amide derivative methanandamide (20 microM; 20 +/- 2% decrease in WT; 4 +/- 6% increase in TASK-1-/-). Current-clamp recordings revealed a muscarine-induced shift in TC neuron activity from burst to tonic firing in both mouse genotypes. Electrocorticograms and sleep/wake times were unchanged in TASK-1-/- mice. In conclusion, our findings demonstrate a significant contribution of TASK-1 channels to ISO in DLG TC neurons, although the genetic knockout of TASK-1 did not produce severe deficits in the thalamocortical system.

• Correlation of T-channel coding gene expression, IT, and the low threshold Ca2+ spike in the thalamus of a rat model of absence epilepsy

  Authors: Tilman Broicher, Tatyana Kanyshkova, Patrick Meuth, Hans-Christian Pape, Thomas Budde

  Molecular and Cellular Neuroscience.

  T-type Ca2+ current-dependent burst firing of thalamic neurons is thought to be involved in the hyper-synchronous activity observed during absence seizures. Here we investigate the correlationT-type Ca2+ current-dependent burst firing of thalamic neurons is thought to be involved in the hyper-synchronous activity observed during absence seizures. Here we investigate the correlation between the expression of T-channel coding genes (α1G, -H, -I), T-type Ca2+ current, and the T-current-dependent low threshold Ca2+ spike in three functionally distinct thalamic nuclei (lateral geniculate nucleus; centrolateral nucleus; reticular nucleus) in a rat model of absence epilepsy, the WAG/Rij rats, and a non-epileptic control strain, the ACI rats. The lateral geniculate nucleus and centrolateral nucleus were found to primarily express α1G and α1I, while the reticular thalamic nucleus expressed α1H and α1I. Expression was higher in WAG/Rij when compared to ACI. The T-type Ca2+ current properties matched the predictions derived from the expression pattern analysis. Current density was larger in all nuclei of WAG/Rij rats when compared to ACI and correlated with LTS size and the minimum LTS generating slope, while T-type Ca2+ current voltage dependency correlated with the LTS onset potential.