124,600 research outputs found
Multiple Shaker Potassium Channels in a Primitive Metazoan
No full textVoltage-gated potassium channels are critical elements in providing functional diversity in nervous systems. The diversity of voltage-gated K+ channels in modern triploblastic metazoans (such as mollusks, arthropods and vettebrates) is provided primarily by four gene subfamilies (Shaker, Shal, Shab, and Shaw), but there has been no data from the ancient diploblastic metazoans until now. Diploblasts, represented by jellyfish and other coelenterates, arose during the first major metazoan radiation and are the most structurally primitive animals to have true nervous systems. By comparing the K+ channels of diploblasts and triploblasts, we may determine the fundamental set of K+ channels present in the first nervous systems. We now report the isolation of two Shaker subfamily cDNA clones, jShak1 and jShak2, from the hydrozoan jellyfish Polyorchis penicillafus (Phylum Cnidaria). JShakl and jShak2 express transient outward currents in Xenopus oocytes most similar to Shaker currents from Drosophila in their rates of inactivation and recovery from inactivation. The finding of multiple Shaker subfamily genes is significant in that multiple Shaker genes also exist in mammals. In Drosophila, multiple Shaker channels are also produced, but by a mechanism of alternative splicing. Thus, the Shaker K+ channel subfamily had an established functional identity prior to the first major radiation of metazoans, and multiple forms of Shaker channels have been independently selected for in a wide range of metazoans
Frobeniusmatrizen maximaler parabolischer Untergruppen in GL (n,q)
No full textJürgens U. Frobeniusmatrizen maximaler parabolischer Untergruppen in GL (n,q). Berichte aus der Mathematik. Aachen: Shaker; 1997
Mechanism of N-Type Inactivation in Shaker Potassium Channels
No full textHyperexcitabilité est l'un des changements les plus importants observés dans de nombreuses maladies neuro-dégénératives telles que la sclérose latérale amyotrophique (SLA) et la maladie d'Alzheimer. De nombreuses recherches études se sont concentrées sur la réduction de l'hyperexcitabilité, soit en inactivant les canaux sodiques ce qui va réduire la génération de potentiels d'action, soit en prolongeant l'ouverture des canaux potassiques ce qui va qui ramener la membrane à son état de repos et réduire l’activité des neurones. Ainsi, pour cibler l'hyperexcitabilité, il faut tout d’abord comprendre les différents aspects de la fonction des canaux ioniques au niveau.
Les objectifs des travaux présentés dans cette thèse consistent à déterminer le mécanisme d'inactivation dans les canaux potassiques Shaker. Les canaux Shaker Kv s'inactivent rapidement pour culminer le potentiel d'action et maintenir l'homéostasie des cellules excitables. L'inactivation de type N est causée par les 46 premiers acides aminés situés de l'extrémité N-terminale du canal, encore appelé, peptide d'inactivation (IP). De nombreuses études mutationnelles ont caractérisé l'inactivation de type N au niveau fonctionnel, cependant, la position de l'IP à l'état de repos et leur transition lors de l'inactivation est encore débattue. L'objectif de la première étude consiste à évaluer le mouvement des IP pendant leur inactivation à l'aide de la fluorométrie en voltage imposé. En insérant un acide aminé non naturel, la 3-[(6-acétyl-2-naphtalényl) amino]-L-alanine (Anap), qui est sensible aux changements d'environnement, nous avons identifié séparément les mouvements de la boule et de la chaîne. Nos données suggèrent que l'inactivation de type N se produit dans un mouvement biphasique en libérant d'abord le IP, ce qui va bloquer le pore du côté cytoplasmique. Pour affiner davantage la position de repos des IP, nous avons utilisé le transfert d'énergie de résonance à base de lanthanide et le métal de transition FRET. Nous proposons que le IP se situe dans la fenêtre formée par le canal et le domaine T1, interagissant avec les résidus acides-aminés du domaine T1.
Dans notre deuxième étude, nous avons montré que le ralentissement de l'inactivation de type N observé dans la première étude est causée par une expression élevée des canaux Shaker. En effet, l'extrémité C-terminale du canal interagit avec les protéines d'échafaudage associées à la membrane pour la formation d'amas. Nous avons aussi montré qu'en tronquant les quatre derniers résidus C-terminaux impliqués dans la formation des amas, nous empêchons également le ralentissement de la cinétique d'inactivation dans les canaux Shaker. Nous avons également démontré que l'inactivation lente de type N n'est pas affectée par l'accumulation des cations potassiques [K+] externe ou toute diaphonie entre les sous-unités voisines. Cette étude élucide non seulement la cause du ralentissement de l'inactivation, mais montre également que les canaux modifient leur comportement en fonction des conditions d'expression. Les résultats trouvés au niveau moléculaire ne peuvent donc pas toujours être extrapolés au niveau cellulaire.Hyperexcitability of neurons is a major symptom observed in many degenerative diseases such as ALS and Alzheimer’s disease. A lot of research is focused on reducing hyperexcitability, either by inactivating sodium channels that will reduce the generation of action potentials, or by prolonging the opening of potassium channels which will help to bring the membrane back to resting state and thus, reduce firing frequency of neurons. At the molecular level, it is important to understand different aspects of ion channel function to target hyperexcitability.
The aim of this thesis was to investigate in two projects the inactivation mechanism in Shaker potassium channels. Shaker Kv channels inactivate rapidly to culminate the action potential and maintain the homeostasis of excitable cells. The so-called N-type inactivation is caused by the first 46 amino acids of the N-terminus of the channel, known as the inactivation peptide (IP). Numerous mutational studies have characterized N-type inactivation functionally, however, the position of the IP in the resting state and its transition during inactivation is still debated. The aim of the first project was to track the movement of IP during inactivation using voltage clamp fluorometry. By inserting an unnatural amino acid, 3-[(6-acetyl-2-naphthalenyl) amino]-L-alanine (Anap), which is sensitive to changes in environment, we identified the movements of ball and chain separately. Our data suggests that N-type inactivation occurs in a biphasic movement by first releasing the IP, which then blocks the pore from the cytoplasmic side. To further narrow down the resting position of the inactivation peptide, we used Lanthanide-based Resonance Energy transfer and transition metal FRET. We propose that the inactivation peptide is located in the window formed by the channel and the T1 domain, interacting with the acidic residues of the T1 domain.
In a follow-up study, we explored the reason underlying slow inactivation kinetics observed during the study of N-type inactivation in the first project. High expression of Shaker channels results in slowing of the N-type inactivation. The C-terminus of the channel interacts with membrane associated scaffold proteins for cluster formation. In this study, we have shown that by truncating the last four C-terminal residues involved in cluster formation, and hence preventing channel clustering, we also prevent slowing of the inactivation kinetics in Shaker channels. We also showed that slow N-type inactivation is not affected by accumulation of external [K+] or any crosstalk between the neighboring subunits. The second project not only elucidates the cause of the inactivation slow-down but illustrates that the channels alter their behavior dependent on the expression conditions. Results found on the molecular level can thus not always be extrapolated to the cellular level
Algen deep under. Zonierung und Anpassung im Rahmen meeresbiologischer Exkursionen
No full textPreisfeld A, Grotjohann N. Algen deep under. Zonierung und Anpassung im Rahmen meeresbiologischer Exkursionen. In: Beiträge zur biologischen Bildung. Vol 5. Aachen: Shaker; 2005: 23-32
Multiple Shaker potassium channels in a primitive metazoan
No full textVoltage-gated potassium channels are critical elements in providing functional diversity in nervous systems. The diversity of voltage-gated K+ channels in modern triploblastic metazoans (such as mollusks, arthropods and vertebrates) is provided primarily by four gene subfamilies (Shaker, Shal, Shab, and Shaw), but there has been no data from the ancient diploblastic metazoans until now. Diploblasts, represented by jellyfish and other coelenterates, arose during the first major metazoan radiation and are the most structurally primitive animals to have true nervous systems. By comparing the K+ channels of diploblasts and triploblasts, we may determine the fundamental set of K+ channels present in the first nervous systems. We now report the isolation of two Shaker subfamily cDNA clones, jShak1 and jShak2, from the hydrozoan jellyfish Polyorchis penicillatus (Phylum Cnidaria). JShak1 and jShak2 express transient outward currents in Xenopus oocytes most similar to Shaker currents from Drosophila in their rates of inactivation and recovery from inactivation. The finding of multiple Shaker subfamily genes is significant in that multiple Shaker genes also exist in mammals. In Drosophila, multiple Shaker channels are also produced, but by a mechanism of alternative splicing. Thus, the Shaker K+ channel subfamily had an established functional identity prior to the first major radiation of metazoans, and multiple forms of Shaker channels have been independently selected for in a wide range of metazoans.</jats:p
Gambierol and n-alkanols inhibit Shaker Kv channel via distinct binding sites outside the <tex>K^{+}$</tex> pore
No full textAbstract: The marine polycyclic-ether toxin gambierol and 1-butanol (n-alkanol) inhibit Shaker-type Kv channels by interfering with the gating machinery. Competition experiments indicated that both compounds do not share an overlapping binding site but gambierol is able to affect 1-butanol affinity for Shaker through an allosteric effect. Furthermore, the Shaker-P475A mutant, which inverses 1-butanol effect, is inhibited by gambierol with nM affinity. Thus, gambierol and 1-butanol inhibit Shaker-type Kv channels via distinct parts of the gating machinery
Was hilft Studierenden, das wissenschaftliche Schreiben in der Fremdsprache zu lernen? – Die subjektive Wahrnehmung von Schreibfördermaßnahmen im universitären Kontext
No full textBallweg S. Was hilft Studierenden, das wissenschaftliche Schreiben in der Fremdsprache zu lernen? – Die subjektive Wahrnehmung von Schreibfördermaßnahmen im universitären Kontext. In: Merkelbach C, ed. Mehr Sprache(n) lernen. Mehr Sprache(n) lehren. Aachen: Shaker; 2015: 73-96
Fruit abscission pattern of ‘Valencia’ orange with canopy shaker system
No full textFruit detachment can occur due to natural causes or be mechanically performed by a
combination of mechanical stresses that cause tissue breakage in the plant. Forced abscission
should not coincide with natural abscission zones (AZ). Abscission zones are very important in
citrus harvesting both in terms of the destination market and of the possible damage caused to
the tree or fruit. The objective of this study is to determine the abscission pattern of sweet
oranges with a canopy shaker and compare it with other detachment systems. Five plots of
Valencia oranges were tested during the 2017 and 2018 harvesting seasons, using a commercial
tractor-drawn canopy shaker. The diameter, weight and breakage type were evaluated in the
cases of natural fall, snap method, mechanical harvesting with canopy shaker, and pull test.
Breakage type AZ-C predominated in natural fall (89.0%) and the snap method (79.5%). Similarly,
AZ-A predominated for the canopy shaker (58.8%) and pull test (45.3%). Mechanical action on
the fruit produced peel tear by breaking the flavedo, which reached highest frequency in the
snap method (7.6%). Peel tear breakage required a mean fruit detachment force value of 99.3
N, higher than the average abscission values for AZ-C (88.7 N) and AZ-A (66.6 N). The fruit that
remained on the tree after canopy shaker harvesting showed lower mean values of fruit
detachment force (16.3%) than the pre-harvest fruit. The frequency of fruit with calyx with the
canopy shaker and snap methods was similar, with a mean value of 36%
Transnational Migration and Development: A Critical Analysis of the New Enthusiasm
No full textFaist T. Transnational Migration and Development: A Critical Analysis of the New Enthusiasm. In: Berggren E, Likic-Brboric B, Tokzös G, Trimikliniotis N, eds. Irregular Migration, Informal Labour and Community. A challenge for Europe. Maastricht: Shaker; 2007: 332-350
Einflussfaktoren beim Fremd-/Zweitsprachenlernen: Wie das Ernstnehmen von Mehrsprachigkeit positive Emotionen im Unterricht stärken könnte
No full textRiemer C. Einflussfaktoren beim Fremd-/Zweitsprachenlernen: Wie das Ernstnehmen von Mehrsprachigkeit positive Emotionen im Unterricht stärken könnte. In: Lindemann B, Marx N, Seiffert H, eds. (Mehr)Sprachen lernen, lehren, leben. 1st ed. Düren: Shaker; 2025: 134–137
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