scholarly journals Selective Proton-Mediated Transport by Electrogenic K+-Binding Macrocycles

Chemistry ◽  
2020 ◽  
Vol 2 (1) ◽  
pp. 11-21
Author(s):  
Yu-Hao Li ◽  
Shao-Ping Zheng ◽  
Dawei Wang ◽  
Mihail Barboiu
Keyword(s):  
Ion Channels ◽  
Therapeutic Agents ◽  
K Channel ◽  
Transport Activity ◽  
Selective Activation ◽  
K Channels ◽  
High K ◽  
Carbonyl Cyanide ◽  
Self Assembled ◽  
K Transport

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.

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

2020 ◽  
Vol 56 (8) ◽  
pp. 1211-1214 ◽  
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.

Potassium secretion and the regulation of distal nephron K channels

1999 ◽  
Vol 277 (6) ◽  
pp. F821-F825 ◽  
Author(s):  
Lawrence G. Palmer
Keyword(s):  
Regulatory Process ◽  
Distal Nephron ◽  
K Channels ◽  
Nephron Segments ◽  
High K ◽  
Potassium Secretion ◽  
K Transport

K-selective channels in the luminal membranes of distal nephron segments form a key pathway for the secretion of K ions into the urine. This process is important to the control of K balance, particularly under conditions of normal or high K intake. This brief review will cover three issues: 1) the identification of apical K channels, 2) the role of these channels in the maintenance of K homeostasis, and 3) the role of aldosterone in this regulatory process. The large amount of literature on renal K transport has been elegantly summarized in a recent review in this journal [G. Giebisch. Am. J. Physiol.274 ( Renal Physiol. 43): F817–F833, 1998]. Here I will focus on a few prominent unsolved problems.

Docosahexaenoic Acid-Induced Vasorelaxation in Hypertensive Rats: Mechanisms of Action

2000 ◽  
Vol 2 (2) ◽  
pp. 85-95 ◽  
Author(s):  
Mary B. Engler ◽  
Marguerite M. Engler
Keyword(s):  
Nitric Oxide ◽  
Inhibitory Effect ◽  
Significant Inhibition ◽  
Isometric Tension ◽  
K Channel ◽  
Omega 3 ◽  
Hypertensive Rats ◽  
Blood Pressure Lowering Effect ◽  
K Channels ◽  
High K

The authors investigated the vasorelaxant properties of the omega-3 fatty acid, docosahexaenoic (DHA, 22:6n-3), and the possible involvement of endothelium-derived nitric oxide, prostanoids, opening of K+ channels, and/or modulation of calcium-mediated events. Isolated aorta from male spontaneously hypertensive rats (SHR) (age 16-17 weeks) were used to measure isometric tension. DHA-induced (1-100 mol/l) relaxation was examined following contraction to norepinephrine (NE) (10– 6 mol/l) or high-K+ (80 mmol/l) solution in the presence and absence of various inhibitors and calcium-containing solution. DHA acid induced a significant vasorelaxant effect in both NE and high-K+-induced contracted SHR aortic rings, although DHA relaxations were greater in high-K+-induced contracted rings. In the absence of extracellular calcium, DHA (5-30 mol/l) inhibited the initial phasic and sustained components of NE-induced contraction under different conditions. Inhibition of nitric oxide synthesis by N•-nitro-L-arginine methyl ester hydrochloride (100 mol/l) had no effect on DHA relaxations; however, indomethacin or nifedipine caused significant inhibition at• 30 mol/l DHA. The K+ channel blocker, glibenclamide, but not tetraethyl-ammonium, also had an inhibitory effect on DHA-induced relaxation. These results indicate that DHA’s vasorelaxant actions in SHR aorta are independent of endothelium-derived nitric oxide; however, at DHA concentrations• 30 mol/l, vasodilatory prostanoids that activate AT Psensitive K+ channels (KATP) may be involved. At lower concentrations, DHA-induced relaxation appears to be attributed to modulation of intracellular Ca2+release and L-type Ca2+channels in vascular smooth muscle cells. The vasorelaxant properties of DHA may contribute, in part, to the blood pressure–lowering effect of dietary fish oil in this hypertensive model.

Stereoselectivity of Bupivacaine in Local Anesthetic–sensitive Ion Channels of Peripheral Nerve 

1999 ◽  
Vol 91 (3) ◽  
pp. 786-786 ◽  
Author(s):  
Carla Nau ◽  
Werner Vogel ◽  
Gunter Hempelmann ◽  
Michael E. Bräu
Keyword(s):  
Ion Channels ◽  
Peripheral Nerve ◽  
Binding Site ◽  
Local Anesthetic ◽  
Rate Constants ◽  
Nerve Fibers ◽  
K Channel ◽  
Channel Block ◽  
K Channels ◽  
Ic50 Values

Background The local anesthetic bupivacaine exists in two stereoisomeric forms, R(+)- and S(-)-bupivacaine. Because of its lower cardiac and central nervous system toxicity, attempts were made recently to introduce S(-)-bupivacaine into clinical anesthesia. We investigated stereoselective actions of R(+)-and S(-)-bupivacaine toward two local anesthetic-sensitive ion channels in peripheral nerve, the Na+ and the flicker K+ channel. Methods In patch-clamp experiments on enzymatically demyelinated peripheral amphibian nerve fibers, Na+ and flicker K+ channels were investigated in outside-out patches. Half-maximum inhibiting concentrations (IC50) were determined. For the flicker K+ channel, simultaneous block by R(+)-bupivacaine and S(-)-bupivacaine was analyzed for competition and association (k1) and dissociation rate constants (k(-1)) were determined. Results Both channels were reversibly blocked by R(+)- and S(-)-bupivacaine. The IC50 values (+/- SEM) for tonic Na+ channel block were 29+/-3 microM and 44+/-3 microM, respectively. IC50 values for flicker K+ channel block were 0.15+/-0.02 microM and 11+/-1 microM, respectively, resulting in a high stereopotency ratio (+/-) of 73. Simultaneously applied enantiomers competed for a single binding site. Rate constants k1 and k(-1) were 0.83+/-0.13x10(6) M(-1) x S(-1) and 0.13+/-0.03 s(-1), respectively, for R(+)-bupivacaine and 1.90+/-0.20x10(6) M(-1) x s(-1) and 8.3+/-1.0 s(-1), respectively, for S(-)-bupivacaine. Conclusions Bupivacaine block of Na+ channels shows no salient stereoselectivity. Block of flicker K+ channels has the highest stereoselectivity ratio of bupivacaine action known so far. This stereoselectivity derives predominantly from a difference in k(-1), suggesting a tight fit between R(+)-bupivacaine and the binding site. The flicker K+ channel may play an important role in yet unknown toxic mechanisms of R(+)-bupivacaine.

scholarly journals Halothane Inhibits an Intermediate Conductance Ca2+-activated K+Channel by Acting at the Extracellular Side of the Ionic Pore

2003 ◽  
Vol 99 (6) ◽  
pp. 1340-1345 ◽  
Author(s):  
Mitsuko Hashiguchi-Ikeda ◽  
Tsunehisa Namba ◽  
Takahiro M. Ishii ◽  
Taizo Hisano ◽  
Kazuhiko Fukuda
Keyword(s):  
Ion Channels ◽  
K Channel ◽  
Xenopus Laevis Oocytes ◽  
Gamma Aminobutyric Acid ◽  
Time Constants ◽  
K Channels ◽  
Pore Domain ◽  
Inside Out ◽  
Gated Ion Channels ◽  
Ligand Gated Ion Channels

Background Actions of volatile anesthetics on ligand-gated ion channels, such as gamma-aminobutyric acid type A receptors, have been studied extensively. However, actions on other types of channels, such as K+ channels, are poorly understood. The authors previously showed that a Ca2+-activated K+ channel, IK, is sensitive to halothane, whereas SK1, another Ca2+-activated K+ channel, is insensitive. To explore how halothane acts on Ca2+-activated K+ channels, chimeras between IK and SK1 were constructed, and halothane sensitivity was analyzed. Methods IK, SK1, and chimera channels were expressed in Xenopus laevis oocytes. Currents of expressed channels were measured in the presence of 10 microm Ca2+ by excised patch clamp analysis. Time constants of inhibition by halothane were compared between inside-out and outside-out patch configurations. Results Currents from chimera channels possessing the pore domain derived from IK were inhibited by halothane, whereas those possessing the SK1 pore domain were insensitive. Time constants of inhibition by halothane were significantly smaller in the outside-out patches than in the inside-out patches of both wild-type IK and a chimera with pore domain of IK. Conclusions It is suggested that halothane interacts with the extracellular part of the ionic pore of IK. Whether this type of interaction is involved in the mechanism of anesthetic actions on ligand-gated ion channels warrants further investigation.

scholarly journals Role of 20-HETE in mediating the effect of dietary K intake on the apical K channels in the mTAL

2001 ◽  
Vol 280 (2) ◽  
pp. F223-F230 ◽  
Author(s):  
Ruimin Gu ◽  
Yuan Wei ◽  
Houli Jiang ◽  
Michael Balazy ◽  
Wenhui Wang
Keyword(s):  
Gas Chromatography Mass Spectrometry ◽  
K Channel ◽  
Thick Ascending Limb ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Deficient Diet ◽  
K Channels ◽  
Medullary Thick Ascending Limb ◽  
High K

We have used the patch-clamp technique to study the effect of dietary K intake on the apical K channels in the medullary thick ascending limb (mTAL) of rat kidneys. The channel activity, defined by the number of channels in a patch and the open probability ( NP o), of the 30- and 70-pS K channels, was 0.18 and 0.11, respectively, in the mTAL from rats on a K-deficient diet. In contrast, NP o of the 30- and 70-pS K channels increased to 0.60 and 0.80, respectively, in the tubules from animals on a high-K diet. The concentration of 20-hydroxyeicosatetraenoic acid (20-HETE) measured with gas chromatography-mass spectrometry was 0.8 pg/μg protein in the mTAL from rats on a high-K diet and increased significantly to 4.6 pg/μg protein in the tubules from rats on a K-deficient diet. Addition of N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS) or 17-octadecynoic acid (17-ODYA), agents that inhibit the formation of 20-HETE, had no significant effect on the activity of the 30-pS K channels. However, DDMS/17-ODYA significantly increased the activity of the apical 70-pS K channel from 0.11 to 0.91 in the mTAL from rats on a K-deficient diet. In contrast, inhibition of the cytochrome P-450 metabolism of arachidonic acid increased NP o from 0.64 to 0.81 in the tubules from animals on a high-K diet. Furthermore, the sensitivity of the 70-pS K channel to 20-HETE was the same between rats on a high-K diet and on a K-deficient diet. Finally, the pretreatment of the tubules with DDMS increased NP o of the 70-pS K channels in the mTAL from rats on a K-deficient diet to 0.76. We conclude that an increase in 20-HETE production is involved in reducing the activity of the apical 70-pS K channels in the mTAL from rats on a K-deficient diet.

scholarly journals Endothelium-dependent responses in human isolated thyroid arteries from donors

2004 ◽  
Vol 181 (3) ◽  
pp. 379-384 ◽  
Author(s):  
B Torondel ◽  
JM Vila ◽  
G Segarra ◽  
P Lluch ◽  
P Medina ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Dominant Role ◽  
Human Thyroid ◽  
K Channel ◽  
Organ Donors ◽  
Inhibitory Effects ◽  
K Channels ◽  
High K ◽  
Inwardly Rectifying ◽  
Endothelium Dependent Relaxation

The functional properties of the endothelium of human thyroid arteries remain unexplored. We investigated the intervention of nitric oxide (NO), prostacyclin (PGI(2)) and endothelium-derived hyperpolarizing factor (EDHF) in the responses to acetylcholine and noradrenaline in isolated thyroid arteries obtained from multi-organ donors. Artery rings were suspended in organ baths for isometric recording of tension. The contribution of NO, PGI(2) and EDHF to endothelium-dependent relaxation was determined by the inhibitory effects of N(G)-monomethyl-L-arginine (L-NMMA), indomethacin, and K(+) channel inhibitors respectively. Acetylcholine induced concentration-dependent relaxation; this effect was not modified by indomethacin and was only partly reduced by L-NMMA, but was abolished in endothelium-denuded rings. The relaxation resistant to indomethacin and L-NMMA was abolished by using either apamin combined with charybdotoxin, ouabain plus barium, or a high-K(+) solution. Noradrenaline induced concentration-dependent contractions which were of greater magnitude in arteries denuded of endothelium or in the presence of L-NMMA.In conclusion, the results indicate that in human thyroid arteries the endothelium significantly modulates responses to acetylcholine and noradrenaline through the release of NO and EDHF. EDHF plays a dominant role in acetylcholine-induced relaxation through activation of Ca(2+)-activated K(+) channels, inwardly rectifying K(+) channels and Na(+)-K(+)-ATPase.

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

2015 ◽  
Vol 146 (2) ◽  
pp. 133-146 ◽  
Author(s):  
Ignacio Díaz-Franulic ◽  
Romina V. Sepúlveda ◽  
Nieves Navarro-Quezada ◽  
Fernando González-Nilo ◽  
David Naranjo
Keyword(s):  
Energy Gap ◽  
Bk Channel ◽  
Selectivity Filter ◽  
K Channel ◽  
Detectable Effect ◽  
Structural Determinants ◽  
K Channels ◽  
Ion Translocation ◽  
Unitary Conductance ◽  
K Transport

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 Å for all 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 Å. 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 ∼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 ∼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 ∼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.

scholarly journals Binding of κ-Conotoxin PVIIA to Shaker K+ Channels Reveals Different K+ and Rb+ Occupancies within the Ion Channel Pore

2004 ◽  
Vol 124 (1) ◽  
pp. 71-81 ◽  
Author(s):  
Anna Boccaccio ◽  
Franco Conti ◽  
Baldomero M. Olivera ◽  
Heinrich Terlau
Keyword(s):  
Ion Channel ◽  
Open Channel ◽  
K Channel ◽  
Closed Channel ◽  
Channel Pore ◽  
K Channels ◽  
Ion Channel Pore ◽  
Structural Work ◽  
High K ◽  
Insight Into

The x-ray structure of the KcsA channel at different [K+] and [Rb+] provided insight into how K+ channels might achieve high selectivity and high K+ transit rates and showed marked differences between the occupancies of the two ions within the ion channel pore. In this study, the binding of κ-conotoxin PVIIA (κ-PVIIA) to Shaker K+ channel in the presence of K+ and Rb+ was investigated. It is demonstrated that the complex results obtained were largely rationalized by differences in selectivity filter occupancy of this 6TM channels as predicted from the structural work on KcsA. κ-PVIIA inhibition of the Shaker K+ channel differs in the closed and open state. When K+ is the only permeant ion, increasing extracellular [K+] decreases κ-PVIIA affinity for closed channels by decreasing the “on” binding rate, but has no effect on the block of open channels, which is influenced only by the intracellular [K+]. In contrast, extracellular [Rb+] affects both closed- and open-channel binding. As extracellular [Rb+] increases, (a) binding to the closed channel is slightly destabilized and acquires faster kinetics, and (b) open channel block is also destabilized and the lowest block seems to occur when the pore is likely filled only by Rb+. These results suggest that the nature of the permeant ions determines both the occupancy and the location of the pore site from which they interact with κ-PVIIA binding. Thus, our results suggest that the permeant ion(s) within a channel pore can determine its functional and pharmacological properties.

Vasopressin increases density of apical low-conductance K+ channels in rat CCD

1993 ◽  
Vol 264 (3) ◽  
pp. F502-F509 ◽  
Author(s):  
A. C. Cassola ◽  
G. Giebisch ◽  
W. Wang
Keyword(s):  
Collecting Duct ◽  
Phosphodiesterase Inhibitor ◽  
K Channel ◽  
Channel Activity ◽  
Dibutyryl Camp ◽  
Open Probability ◽  
Simultaneous Application ◽  
K Channels ◽  
Principal Cells ◽  
High K

The effect of arginine vasopressin (AVP) on the low-conductance K+ channel in the apical membrane of rat cortical collecting duct (CCD) principal cells from animals on a control and high-K+ diet was studied using patch-clamp techniques. AVP stimulated apical low-conductance K+ channel activity in both control and high-K+ animals: application of 110-220 pM AVP induced a significant increase in the density of low-conductance K+ channels. In the presence of phosphodiesterase inhibitor (3-isobutyl-1-methylxanthine), administration of 22 pM AVP also increased channel activity. The action of AVP on low-conductance K+ channel activity was mimicked by simultaneous application of forskolin and 3-isobutyl-1-methylxanthine. Exogenously applied N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (dibutyryl-cAMP, 0.4-0.8 mM) also increased apical low-conductance K+ channel activity. Since channel open probability (Po) was almost saturated in the absence of AVP, the increase of channel activity induced by AVP, forskolin, and dibutyryl-cAMP resulted predominantly from stimulating previously silent K+ channels. We conclude that AVP induces an increase of low-conductance K+ channel activity of principal cells in rat CCD by the stimulation of cAMP-dependent protein kinase. The AVP-induced increase of low-conductance K+ channel activity can thus significantly contribute to the hormone-induced K+ secretion in the rat CCD.

Sign in / Sign up

Export Citation Format

Share Document