Finding of a KCl-independent, electrogenic, and ATP-driven H+-pumping activity in rat light gastric membranes and its effect on the membrane K+ transport activity.

Synthetic K+-binding macrocycles have potential as therapeutic agents for diseases associated with KcsA K+ channel dysfunction. We recently discovered that artificial self-assembled n-alkyl-benzoureido-15-crown-5-ether form selective ion-channels for K+ cations, which are highly preferred to Na+ cations. Here, we describe an impressive selective activation of the K+ transport via electrogenic macrocycles, stimulated by the addition of the carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP) proton carrier. The transport performances show that both the position of branching or the size of appended alkyl arms favor high transport activity and selectivity SK+/Na+ up to 48.8, one of the best values reported up to now. Our study demonstrates that high K+/Na+ selectivity obtained with natural KcsA K+ channels is achievable using simpler artificial macrocycles displaying constitutional functions.

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Cell volume and metabolic dependence of NEM-activated K+-Cl- flux in human red blood cells

AJP Cell Physiology ◽

10.1152/ajpcell.1985.249.1.c124 ◽

1985 ◽

Vol 249 (1) ◽

pp. C124-C128 ◽

Cited By ~ 45

Author(s):

P. K. Lauf ◽

C. M. Perkins ◽

N. C. Adragna

Keyword(s):

Red Blood Cells ◽

Cell Volume ◽

Blood Cells ◽

Time Course ◽

Transport Activity ◽

Human Red Blood Cells ◽

Atp Breakdown ◽

The Difference ◽

Metabolic Dependence ◽

K Transport

The effects of incubation in anisosmotic media and of metabolic depletion on ouabain-resistant (OR) Cl--dependent K+ influxes stimulated by N-ethylmaleimide (NEM) were studied in human red blood cells using Rb+ as K+ analogue. The NEM-stimulated but not the basal Rb+-Cl- influx measured in phosphate-buffered anisosmotic media was found to be cell volume dependent. When cellular ATP, [ATP]c, was lowered to less than 0.10 of its initial level by exposure to nonmetabolizable 2-deoxy-D-glucose, the NEM-stimulated but not the basal Cl--dependent Rb+ influxes were abolished. Metabolically depleted red blood cells subsequently repleted by incubation in glucose plus inosine regained the NEM-inducible Rb+ (K+) transport activity. The difference in the time course of ATP breakdown and Rb+ influx inhibition suggests that energization of the NEM-stimulated Rb+ flux by metabolism may involve factors additional to ATP.

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Electrophysiology of K+ transport by midgut epithelium of lepidopteran insect larvae. IV. A multicompartment model accounts for tetramethylammonium entry into goblet cavities

Journal of Experimental Biology ◽

10.1242/jeb.198.10.2115 ◽

1995 ◽

Vol 198 (10) ◽

pp. 2115-2125

Author(s):

A Koch ◽

D Moffett

Keyword(s):

Goblet Cell ◽

Driving Forces ◽

Short Circuit ◽

Basal Membrane ◽

Open Circuit ◽

Columnar Cell ◽

Transport Activity ◽

Cell Cytoplasm ◽

Experimental Conditions ◽

K Transport

A quantitative model was developed to explain the kinetics of tetramethylammonium (TMA+) movement into and out of the goblet cavities of posterior midgut cells of Manduca sexta based on the data of the accompanying paper, which indicated that TMA+ does not enter the goblet cavity directly from the lumen. The model has two cellular compartments between the lumen and goblet cavity; these have been tentatively identified as the columnar cell and goblet cell cytoplasm. Five transmembrane pathways are included: from lumen to columnar cell, from columnar cell to goblet cell, from goblet cell cytoplasm to goblet cell cavity, and across the basal membrane of each cell type. These pathways need not be channels; they could use endocytotic or exocytotic mechanisms or, in the case of the cell-to-cell passage, septate junctions. However, in all cases, transfer is proportional to the electrochemical gradient. The model was tested against the results obtained after exposure to TMA+ in short-circuited and open-circuited tissues as well as results from an open-circuited tissue that did not develop a large transepithelial potential. Although driving forces for TMA+ across the membrane barriers were quite different in the different experimental conditions, the transfer coefficients from lumen to columnar cell, from columnar to goblet cell and from both cells across the basal membrane were the same. The only transfer coefficient that changed between short-circuit and open-circuit conditions was that from goblet cell cytoplasm to goblet cavity. This value was high under short-circuit conditions (when K+ transport activity is high), but low under open-circuit conditions (when K+ transport activity is low). The model suggests a hypothesis in which TMA+ enters the goblet cavity by an indirect route across the cell membrane of columnar cells, and thence passes to the goblet cell cytoplasm through intercellular junctions. Results from experiments with cytochalasin E suggest that the actin-based cytoskeleton is involved in limiting cellcell coupling. In this model, TMA+ passes from the goblet cell cytoplasm to the goblet cavity via the K+/nH+ antiport believed to mediate active transepithelial K+ transport. However, although actively transported K+ is believed to pass from goblet cavity to lumen, TMA+ cannot.

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Insights into the Mechanisms of Transport and Regulation of the Arabidopsis High-affinity K+ Transporter HAK5

Plant Physiology ◽

10.1093/plphys/kiab028 ◽

2021 ◽

Author(s):

Reyes Ródenas ◽

Paula Ragel ◽

Manuel Nieves-Cordones ◽

Almudena Martínez-Martínez ◽

Jesús Amo ◽

...

Keyword(s):

Structural Model ◽

Molecular Model ◽

3D Structure ◽

Nutrition Information ◽

Transport Activity ◽

Selective Filter ◽

High Affinity ◽

C Terminus ◽

Functional Relevance ◽

K Transport

Abstract The high-affinity K+ transporter HAK5 from Arabidopsis is essential for K+ acquisition and plant growth at low micromolar K+ concentrations. Despite its functional relevance in plant nutrition, information about functional domains of HAK5 is scarce. Its activity is enhanced by phosphorylation via the AtCIPK23/AtCBL1-9 complex. Based on the recently published 3D-structure of the bacterial ortholog KimA from Bacillus subtilis, we have modeled AtHAK5 and, by a mutational approach, identified residues G67, Y70, G71, D72, D201, and E312 as essential for transporter function. According to the structural model, residues D72, D201, and E312 may bind K+, whereas residues G67, Y70, and G71 may shape the selective filter for K+, which resembles that of K+shaker-like channels. In addition, we show that phosphorylation of residue S35 by AtCIPK23 is required for reaching maximal transport activity. Serial deletions of the AtHAK5 C-terminus disclosed the presence of an autoinhibitory domain located between residues 571 and 633 together with an AtCIPK23-dependent activation domain downstream of position 633. Presumably, autoinhibition of AtHAK5 is counteracted by phosphorylation of S35 by AtCIPK23. Our results provide a molecular model for K+ transport and describe CIPK-CBL-mediated regulation of plant HAK transporters.

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Enhancing K+ transport activity and selectivity of synthetic K+ channels via electron-donating effects

Chemical Communications ◽

10.1039/c9cc08396k ◽

2020 ◽

Vol 56 (8) ◽

pp. 1211-1214 ◽

Cited By ~ 1

Author(s):

Landley Ziluo Zeng ◽

Hao Zhang ◽

Tianxiang Wang ◽

Tianhu Li

Keyword(s):

Ion Transport ◽

Transport Activity ◽

K Channels ◽

High K ◽

K Transport

Electron-withdrawing groups enhance ion transport activity by 160% and selectivity by >50%, leading to high K+/Na+ selectivity of 14.0.

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Novel bumetanide-sensitive K+ transport in preimplantation mouse conceptuses

AJP Cell Physiology ◽

10.1152/ajpcell.1992.263.4.c773 ◽

1992 ◽

Vol 263 (4) ◽

pp. C773-C779 ◽

Cited By ~ 3

Author(s):

L. J. Van Winkle ◽

A. L. Campione

Keyword(s):

Basal Membrane ◽

Hill Coefficient ◽

K Channel ◽

Channel Blockers ◽

The Novel ◽

Transport Activity ◽

Michaelis Constant ◽

Preimplantation Mouse ◽

22Na Uptake ◽

K Transport

Ouabain-resistant K+ transport activity was characterized primarily by measuring Rb+ uptake because 86Rb+ has a more convenient half-life than 42K+. Ouabain-resistant 86Rb+ uptake by mouse two-cell conceptuses and blastocysts was slowed by the K(+)-Na(+)-2Cl- cotransporter inhibitors bumetanide [inhibitory constant (Ki) = 400 nM] and furosemide (Ki approximately 10 microM), but it was insensitive to a variety of K+ channel blockers. This component of 86Rb+ transport was also inhibited by K+ and nonradioactive Rb+ and it was stimulated by Cl-. Nevertheless, neither 36Cl- nor 22Na+ uptake was inhibited by bumetanide, whereas 42K+ uptake was inhibited by both bumetanide and furosemide. Bumetanide-sensitive Rb+ transport in blastocysts had a Hill coefficient of 1.0 and a Michaelis constant value of 3.0 mM. By these criteria, preimplantation conceptuses contain a novel, bumetanide-sensitive K+ transport system that does not cotransport Cl- or Na+. Moreover, bumetanide-sensitive Rb+ uptake was 10 times faster in blastocysts when they were collapsed to expose the basal membrane of the trophectoderm to 86Rb+ in the medium. Therefore, the novel system may be located predominantly in the basal rather than in the apical membrane of the trophectoderm.

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