Pore dimensions and the role of occupancy in unitary conductance of Shaker K channels

Indexación: Web of Science; Scopus.K channels mediate the selective passage of K+ across the plasma membrane by means of intimate interactions with ions at the pore selectivity filter located near the external face. Despite high conservation of the selectivity filter, the K+ transport properties of different K channels vary widely, with the unitary conductance spanning a range of over two orders of magnitude. Mutation of Pro475, a residue located at the cytoplasmic entrance of the pore of the small-intermediate conductance K channel Shaker (Pro475Asp (P475D) or Pro475Gln (P475Q)), increases Shaker's reported. 20-pS conductance by approximately six-and approximately threefold, respectively, without any detectable effect on its selectivity. These findings suggest that the structural determinants underlying the diversity of K channel conductance are distinct from the selectivity filter, making P475D and P475Q excellent probes to identify key determinants of the K channel unitary conductance. By measuring diffusion-limited unitary outward currents after unilateral addition of 2 M sucrose to the internal solution to increase its viscosity, we estimated a pore internal radius of capture of 0.82 for all the three Shaker variants (wild type, P475D, and P475Q). This estimate is consistent with the internal entrance of the Kv1.2/2.1 structure if the effective radius of hydrated K+ is set to 4 A. Unilateral exposure to sucrose allowed us to estimate the internal and external access resistances together with that of the inner pore. We determined that Shaker resistance resides mainly in the inner cavity, whereas only similar to 8% resides in the selectivity filter. To reduce the inner resistance, we introduced additional aspartate residues into the internal vestibule to favor ion occupancy. No aspartate addition raised the maximum unitary conductance, measured at saturating [K+], beyond that of P475D, suggesting an similar to 200-pS conductance ceiling for Shaker. This value is approximately one third of the maximum conductance of the large conductance K (BK) channel (the K channel of highest conductance), reducing the energy gap between their K+ transport rates to similar to 1 kT. Thus, although Shaker's pore sustains ion translocation as the BK channel's does, higher energetic costs of ion stabilization or higher friction with the ion's rigid hydration cage in its narrower aqueous cavity may entail higher resistance.http://jgp.rupress.org/content/146/2/13

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

Regulation of Proliferation by a Mitochondrial Potassium Channel in Pancreatic Ductal Adenocarcinoma Cells

Previous results link the mitochondrial potassium channel Kv1.3 (mitoKv1.3) to the regulation of apoptosis. By synthesizing new, mitochondria-targeted derivatives (PAPTP and PCARBTP) of PAP-1, a specific membrane-permeant Kv1.3 inhibitor, we have recently provided evidence that both drugs acting on mitoKv1.3 are able to induce apoptosis and reduce tumor growth in vivo without affecting healthy tissues and cells. In the present article, by exploiting these new drugs, we addressed the question whether mitoKv1.3 contributes to the regulation of cell proliferation as well. When used at low concentrations, which do not compromise cell survival, both drugs slightly increased the percentage of cells in S phase while decreased the population at G0/G1 stage of cells from two different pancreatic ductal adenocarcinoma lines. Our data suggest that the observed modulation is related to ROS levels within the cells, opening the way to link mitochondrial ion channel function to downstream, ROS-related signaling events that might be important for cell cycle progression

The Bronze Door Panels within the Façade of San Zeno Maggiore, Verona: A Chronological and Liturgical Assessment.

This thesis presents an analysis of the bronze door panels of San Zeno Maggiore, Verona, with reference to the surrounding low relief stone sculptures, textual material relating to Bishop Zeno, the patron saint of the church, and the wider religious and political developments of the late tenth, eleventh and twelfth centuries. In identifying those panels the thesis recognises the way in which the door panels and stone sculptures form a traditional narrative identifying Creation and the Fall on the right juxtaposed with Redemption and Salvation on the left. The core of the thesis focuses on two facets of the bronze door panels: the dating of the panels’ production, and the composition of the doors prior to the earthquake of 1117. The doors are complex and include in their current state panels manufactured by at least two workshops operating in different periods. These are discussed with reference to the works themselves and to recent historical scholarship. The thesis concludes that the panels were manufactured in two periods: the first period may have been either in the Ottonian era (c.960-c.1040) or later in the eleventh century (c.1080); the second period was the later twelfth century (c.1175). The thesis also discusses the stone relief sculptures, carved in 1135-1138, that provide a framework and context for the doors. The second aspect is the baptismal and Paschal lectionary, which incorporates San Zeno’s preferred readings, as the basis for the choice of subjects of the first set of bronze door panels. The massive earthquake of 1117 severely damaged the basilica and some original panels were damaged and discarded. It has not been possible to demonstrate definitively that the sermons and lectionary were known to those who commissioned the panels, but the thesis seeks to show their importance in describing the panel composition. The door panels and stone reliefs assert a symbolic distancing from both Papacy and Empire after the Investiture Controversy. The two lowest stone reliefs, on the left and right of the doorway, represent accounts of Otto and Berengar fighting over Adelaide, and of Theodoric and the wild hunt, respectively. The significance of these narratives is discussed

China Maritime Report No. 14: Chinese Views of the Military Balance in the Western Pacific

This report examines Chinese views about the military balance of power between China and the United States in the Western Pacific. It argues that while there is no single “Chinese” view on this topic, Chinese analysts tend to agree that 1) the gap between the two militaries has narrowed significantly in recent years, 2) the Chinese military still lags in important ways, and 3) Chinese military inferiority vis-à-vis the U.S. increases the further away it operates from the Mainland. In terms of specific areas of relative strength, the Chinese military has shown the greatest improvements in military hardware, but has farther to go in the area of jointness, training, and other military “software.” Nevertheless, despite continued criticism from senior civilian leaders, training quality has likely improved due to a greater focus on realism, and recent military reforms have, to a degree, improved the prospects for jointness.https://digital-commons.usnwc.edu/cmsi-maritime-reports/1013/thumbnail.jp

The (General) Education of Henri(etta) Adams: Living With “the Word”

Eleanor Elson Heginbotham, Professor of English at Concordia University, St. Paul, has been educated, in the broadest sense, around the world. Born in California, she grew up in Washington, D.C., in the world of a pastor whose ministry extended well beyond the Capitol. Married to a Foreign Service Officer after her undergraduate years at the College of Wooster in Ohio, she lived and taught in Liberia, Vietnam, and Indonesia. Later, she taught for 18 years in the Washington suburbs while she pursued her M.A. (1971) and Ph.D. (1992) at the University of Maryland. She received the Marion Freedman Greenblatt Award (all levels, all disciplines) for her teaching and the Bode Award for her dissertation on Emily Dickinson. At Concordia, since 1994, she has taught literature, journalism, and writing classes. She also has presented over a dozen papers at conferences, written a number of articles for scholarly journals, and organized (in collaboration with colleagues) conferences - on Laura Ingalls Wilder, on Emily Dickinson, and in September 2002, the first International Conference of the F. Scott Fitzgerald Society ever hosted by his native city of St. Paul. During her year as a Senior Fulbright Scholar at the University of Hong Kong (1998-99), she taught a full load of classes in American Studies and spoke in other universities in Hong Kong, China, Taiwan, and Thailand. With another Fulbright Scholar in Hong Kong, she arranged a series of viewings and symposia on classic American Films, treated as texts, cinema graphic art and as history. Home again she completed her book, Reading the Fascicles of Emily Dickinson: Dwelling in Possibilities, published by Ohio State University Press in July 2003. Throughout the past 10 years she has appreciated Concordia\u27s support for her teaching, conferences, publishing and general education in the spirit of its stated mission: to prepare students [and faculty] for thoughtful and informed living, for dedicated service to God and humanity, and for the enlightened care of God\u27s creation, all within the context of the Christian Gospel. She retired in June 2004

Developing a capacity test for compulsion in mental health law

Concepts of mental capacity are taking on an increased importance in the mental health law of the United Kingdom. For England and Wales, the proposal to introduce a threshold requirement of ‘impaired decision-making’ into the criteria for detention under sections 2 and 3 of the Mental Health Act 1983 was the first amendment to be voted upon in the House of Lords’ reading of the Mental Health Bill. Despite its emphatic (and whipped) resistance to this amendment, Government lost the vote by a wide margin, although it seems possible, at the time of writing, that the Government will seek to overturn their defeat in the Commons.It is therefore timely to re-examine the role of such capacity tests in mental health legislation dealing with detention and treatment. This paper describes as yet unresolved definitional questions that must be encountered when concepts of mental capacity operate as a threshold for coercive psychiatric detention and/or treatment

The analysis of European lacquer : optimization of thermochemolysis temperature of natural resins

In order to optimize chromatographic analysis of European lacquer, thermochemolysis temperature was evaluated for the analysis of natural resins. Five main ingredients of lacquer were studied: sandarac, mastic, colophony, Manila copal and Congo copal. For each, five temperature programs were tested: four fixed temperatures (350, 480, 550, 650 degrees C) and one ultrafast thermal desorption (UFD), in which the temperature rises from 350 to 660 degrees C in 1 min. In total, the integrated signals of 27 molecules, partially characterizing the five resins, were monitored to compare the different methods. A compromise between detection of compounds released at low temperatures and compounds formed at high temperatures was searched. 650 degrees C is too high for both groups, 350 degrees C is best for the first, and 550 degrees C for the second. Fixed temperatures of 480 degrees C or UFD proved to be a consensus in order to detect most marker molecules. UFD was slightly better for the molecules released at low temperatures, while 480 degrees C showed best compounds formed at high temperatures