Selection of Inhibitor-Resistant Viral Potassium Channels Identifies a Selectivity Filter Site that Affects Barium and Amantadine Block

BACKGROUND:Understanding the interactions between ion channels and blockers remains an important goal that has implications for delineating the basic mechanisms of ion channel function and for the discovery and development of ion channel directed drugs. METHODOLOGY/PRINCIPAL FINDINGS:We used genetic selection methods to probe the interaction of two ion channel blockers, barium and amantadine, with the miniature viral potassium channel Kcv. Selection for Kcv mutants that were resistant to either blocker identified a mutant bearing multiple changes that was resistant to both. Implementation of a PCR shuffling and backcrossing procedure uncovered that the blocker resistance could be attributed to a single change, T63S, at a position that is likely to form the binding site for the inner ion in the selectivity filter (site 4). A combination of electrophysiological and biochemical assays revealed a distinct difference in the ability of the mutant channel to interact with the blockers. Studies of the analogous mutation in the mammalian inward rectifier Kir2.1 show that the T-->S mutation affects barium block as well as the stability of the conductive state. Comparison of the effects of similar barium resistant mutations in Kcv and Kir2.1 shows that neighboring amino acids in the Kcv selectivity filter affect blocker binding. CONCLUSIONS/SIGNIFICANCE:The data support the idea that permeant ions have an integral role in stabilizing potassium channel structure, suggest that both barium and amantadine act at a similar site, and demonstrate how genetic selections can be used to map blocker binding sites and reveal mechanistic features

Review. Leaky Cl--HCO3- exchangers: cation fluxes via modified AE1.

The abundant membrane protein AE1 normally functions as an obligate anion exchanger, with classical carrier properties, in human red blood cells. Recently, four single point mutations of hAE1 have been identified that have lost the anion exchange function, and act as non-selective monovalent cation channels, as shown in both red cell flux and oocyte expression studies. The red cell transport function shows a paradoxical temperature dependence, and is associated with spherocytic and stomatocytic red cell defects, and haemolytic anaemias. Other forms of AE1, including the native AE1 in trout red cells, and the human mutation R760Q show both channel-like and anion exchange properties. The present results point to membrane domains 9 and 10 being important in the functional modification of AE1 activity

Primary red cell hydration disorders: Pathogenesis and diagnosis

31st International Symposium of the International-Society-for-Laboratory-Hematology (ISLH) on Technological Innovations in Laboratory Hematology, Brussels, BELGIUM, 2018Hydration status is critical for erythrocyte survival and is mainly determined by intracellular cation content. Active pumps, passive transporters, and ion channels are the key components of volume homeostasis, whereas water passively fits ionic movements. Whenever cation content increases, erythrocyte swells, whereas it shrinks when cation content decreases. Thus, inappropriate cation leak causes erythrocyte hydration disorders, hemolytic anemia, and characteristic red cell shape abnormalities named stomatocytosis. All types of stomatocytosis either overhydrated or dehydrated are linked to inherited or de novo mutations in genes encoding ion transporters or channels. Although intracellular ion content can be assessed by experimental methods, laboratory diagnosis is guided by a combination of red blood cell parameters and deformability measurement when possible, and confirmed by sequencing of the putative genes. A better knowledge of the mechanisms underlying erythrocyte hydration imbalance will further lead to therapeutic improvements

Magnetic and magnetocaloric properties of the new R3Co4+xAl12-x (R: Tb → Er) with the Gd3Ru4Al12 structure-type

International audienceThe novel intermetallics R3Co4+xAl12-x (R = Tb → Er) crystallize in the hexagonal Gd3Ru4Al12 structure-type where the rare earth atoms form a heavily distorted kagome network. Single crystal X-ray diffraction reveals an unusual 2b substitution site of Co for Al probably driven by steric effects. The four phases order ferromagnetically below 24.0, 17.4, 11.5 and 5.0 K for R = Tb, Dy, Ho and Er, respectively, linearly decreasing with the de Gennes factor of the rare earth. The magnetocaloric properties have been estimated for R = Ho and Er by measuring the magnetization isotherms at various temperatures. The magnetic entropy changes reach maximum values of −12 and −10 J kg−1 K−1 for a magnetic field change from 5 to 0 T. © 2017 Elsevier Lt

NdSrNi0.8Cu0.2O4-δ thin films epitaxially grown by pulsed laser deposition on LaAlO3 and SrTiO3 : a potential electrode for epitaxial regrowth of perovskite structure-based oxides

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