An electrostatic interaction between TEA and an introduced pore aromatic drives spring-in-the-door inactivation in Shaker potassium channels

Slow inactivation of Kv1 channels involves conformational changes near the selectivity filter. We examine such changes in Shaker channels lacking fast inactivation by considering the consequences of mutating two residues, T449 just external to the selectivity filter and V438 in the pore helix near the bottom of the selectivity filter. Single mutant T449F channels with the native V438 inactivate very slowly, and the canonical foot-in-the-door effect of extracellular tetraethylammonium (TEA) is not only absent, but the time course of slow inactivation is accelerated by TEA. The V438A mutation dramatically speeds inactivation in T449F channels, and TEA slows inactivation exactly as predicted by the foot-in-the-door model. We propose that TEA has this effect on V438A/T449F channels because the V438A mutation produces allosteric consequences within the selectivity filter and may reorient the aromatic ring at position 449. We investigated the possibility that the blocker promotes the collapse of the outer vestibule (spring-in-the-door) in single mutant T449F channels by an electrostatic attraction between a cationic TEA and the quadrupole moments of the four aromatic rings. To test this idea, we used in vivo nonsense suppression to serially fluorinate the introduced aromatic ring at the 449 position, a manipulation that withdraws electrons from the aromatic face with little effect on the shape, net charge, or hydrophobicity of the aromatic ring. Progressive fluorination causes monotonically enhanced rates of inactivation. In further agreement with our working hypothesis, increasing fluorination of the aromatic gradually transforms the TEA effect from spring-in-the-door to foot-in-the-door. We further substantiate our electrostatic hypothesis by quantum mechanical calculations

Voltage-Dependent Gating in a “Voltage Sensor-Less” Ion Channel

An unusual mechanism of ion channel regulation generates voltage-dependent gating in the absence of a canonical voltage-sensing domain

Inorganic Polyphosphate Modulates TRPM8 Channels

Polyphosphate (polyP) is an inorganic polymer built of tens to hundreds of phosphates, linked by high-energy phosphoanhydride bonds. PolyP forms complexes and modulates activities of many proteins including ion channels. Here we investigated the role of polyP in the function of the transient receptor potential melastatin 8 (TRPM8) channel. Using whole-cell patch-clamp and fluorescent calcium measurements we demonstrate that enzymatic breakdown of polyP by exopolyphosphatase (scPPX1) inhibits channel activity in human embryonic kidney and F-11 neuronal cells expressing TRPM8. We demonstrate that the TRPM8 channel protein is associated with polyP. Furthermore, addition of scPPX1 altered the voltage-dependence and blocked the activity of the purified TRPM8 channels reconstituted into planar lipid bilayers, where the activity of the channel was initiated by cold and menthol in the presence of phosphatidylinositol 4,5-biphosphate (PtdIns(4,5)P2). The biochemical analysis of the TRPM8 protein also uncovered the presence of poly-(R)-3-hydroxybutyrate (PHB), which is frequently associated with polyP. We conclude that the TRPM8 protein forms a stable complex with polyP and its presence is essential for normal channel activity

Sensing the fuels: glucose and lipid signaling in the CNS controlling energy homeostasis

The central nervous system (CNS) is capable of gathering information on the body’s nutritional state and it implements appropriate behavioral and metabolic responses to changes in fuel availability. This feedback signaling of peripheral tissues ensures the maintenance of energy homeostasis. The hypothalamus is a primary site of convergence and integration for these nutrient-related feedback signals, which include central and peripheral neuronal inputs as well as hormonal signals. Increasing evidence indicates that glucose and lipids are detected by specialized fuel-sensing neurons that are integrated in these hypothalamic neuronal circuits. The purpose of this review is to outline the current understanding of fuel-sensing mechanisms in the hypothalamus, to integrate the recent findings in this field, and to address the potential role of dysregulation in these pathways in the development of obesity and type 2 diabetes mellitus

Die Entwicklung der Arbeit aus der Perspektive ihrer Informatisierung

Die Entwicklung der Arbeit aus der Perspektive ihrer Informatisierung Im Mittelpunkt des Beitrags stehen die Erzeugung und Nutzung von Informationen und In-formationssystemen im Arbeitsprozess und die damit verbundenen Veränderungen der Arbeit. Die historische Entwicklung der Informatisierung der Arbeit wird -ausgehend von dem ersten Auftreten des Handelskapitals und der Buchführung im 13. und 14. Jahrhundert bis zur Durchsetzung eines global verfügbaren "Informationsraums", welcher als neuartiger sozialer Handlungsraum die aktuelle Entwicklung bestimmt - kurz skizziert. Dieser "Informationsraum" bildet das "Rückgrat" moderner Unternehmenskonzepte. Er ist charakteristisch für die modernen, in globalisierten Märkten agierenden horizontalen oder Netzwerkunternehmen. In solchen netzwerkförmigen Organisationsstrukturen erbrachte Teil-arbeiten werden zu in sich konsistenten und zugleich veränderungsoffenen Leistungserstel-lungsprozessen zusammengefügt. Statt in starr vorprogrammierten Funktionsketten findet sich das Subjekt nun in offenen Verweisstrukturen, die durch reflexiven Umgang mit den Infor-mationsobjekten chrakterisiert sind. Hier ist das Funktionieren des Informationssystems von kommunikativ vermittelten Ausdeutungs- und Gestaltungsleistungen des Subjekts abhängig. Dieses ist in Zukunft nicht mehr ausschließlich an den Rand und in die Nischen geschlossener Informationssysteme gedrängt, sondern es muß sich in seinem Denken und Handeln in die Informationssysteme hineinbegeben, um den Anforderungen flexibler Produktionsprozesse gerecht zu werden. Damit entsteht eine neuartige Dichotomie von Chancen und Risiken