Electrophysiological profile after inward rectifier K channel blockade by barium in isolated rabbit hearts. Altered repolarization and unmasked decremental conduction property

We studied block of the internal pore of the ROMK1 inward-rectifier K+ channel by Mg2+ and five quaternary ammoniums (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, and tetrapentylammonium). The apparent affinity of these blockers varied as a function of membrane voltage. As a consequence, the channel conducted K+ current more efficiently in the inward than the outward direction; i.e., inward rectification. Although the size of some monovalent quaternary ammoniums is rather large, the zδ values (which measure voltage dependence of their binding to the pore) were near unity in symmetric 100 mM K+. Furthermore, we observed that not only the apparent affinities of the blockers themselves, but also their dependence on membrane voltage (or zδ), varied as a function of the concentration of extracellular K+. These results suggest that there is energetic coupling between the binding of blocking and permeating (K+) ions, and that the voltage dependence of channel blockade results, at least in part, from the movement of K+ ions in the electrical field. A further quantitative analysis of the results explains why the complex phenomenon of inward rectification depends on both membrane voltage and the equilibrium potential for K+.

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Characterisation of recombinant HERG K+ channel blockade by the Class Ia antiarrhythmic drug procainamide

Biochemical and Biophysical Research Communications ◽

10.1016/s0006-291x(03)00980-x ◽

2003 ◽

Vol 306 (2) ◽

pp. 388-393 ◽

Cited By ~ 22

Author(s):

John M Ridley ◽

James T Milnes ◽

Andrew V Benest ◽

Joe D Masters ◽

Harry J Witchel ◽

...

Keyword(s):

Antiarrhythmic Drug ◽

K Channel ◽

Channel Blockade

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Nucleotide inhibition of the pancreatic ATP-sensitive K+ channel explored with patch-clamp fluorometry

eLife ◽

10.7554/elife.52775 ◽

2020 ◽

Vol 9 ◽

Author(s):

Samuel G Usher ◽

Frances M Ashcroft ◽

Michael C Puljung

Keyword(s):

Nucleotide Binding ◽

Inward Rectifier ◽

K Channel ◽

Data Sets ◽

Channel Activity ◽

Unknown Mechanism ◽

Apparent Affinity ◽

Nucleotide Inhibition ◽

Channel Currents ◽

Combined Data

Pancreatic ATP-sensitive K+ channels (KATP) comprise four inward rectifier subunits (Kir6.2), each associated with a sulphonylurea receptor (SUR1). ATP/ADP binding to Kir6.2 shuts KATP. Mg-nucleotide binding to SUR1 stimulates KATP. In the absence of Mg2+, SUR1 increases the apparent affinity for nucleotide inhibition at Kir6.2 by an unknown mechanism. We simultaneously measured channel currents and nucleotide binding to Kir6.2. Fits to combined data sets suggest that KATP closes with only one nucleotide molecule bound. A Kir6.2 mutation (C166S) that increases channel activity did not affect nucleotide binding, but greatly perturbed the ability of bound nucleotide to inhibit KATP. Mutations at position K205 in SUR1 affected both nucleotide affinity and the ability of bound nucleotide to inhibit KATP. This suggests a dual role for SUR1 in KATP inhibition, both in directly contributing to nucleotide binding and in stabilising the nucleotide-bound closed state.

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The prolonged pulmonary vascular (PV) muscle relaxation time of the newborn(NB) is correctable by K+ channel blockade. ♦ 1465

Pediatric Research ◽

10.1203/00006450-199704001-01484 ◽

1997 ◽

Vol 41 ◽

pp. 247-247

Author(s):

Jaques Belik

Keyword(s):

Relaxation Time ◽

Muscle Relaxation ◽

K Channel ◽

Channel Blockade

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Primary structure and functional expression of a mouse inward rectifier K+ channel and a rat G-protein-coupled muscarinic K+ channel.

Seibutsu Butsuri ◽

10.2142/biophys.36.270 ◽

1996 ◽

Vol 36 (6) ◽

pp. 270-274

Author(s):

Yoshihiro KUBO

Keyword(s):

G Protein ◽

Primary Structure ◽

Functional Expression ◽

Inward Rectifier ◽

K Channel ◽

G Protein Coupled

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Functional expression of a vertebrate inwardly rectifying K+ channel in yeast.

Molecular Biology of the Cell ◽

10.1091/mbc.6.9.1231 ◽

1995 ◽

Vol 6 (9) ◽

pp. 1231-1240 ◽

Cited By ~ 51

Author(s):

W Tang ◽

A Ruknudin ◽

W P Yang ◽

S Y Shaw ◽

A Knickerbocker ◽

...

Keyword(s):

Transcriptional Control ◽

Xenopus Oocytes ◽

Genetic System ◽

Functional Expression ◽

Inward Rectifier ◽

K Channel ◽

Coding Region ◽

Low Potassium ◽

K Current ◽

Inwardly Rectifying

We describe the expression of gpIRK1, an inwardly rectifying K+ channel obtained from guinea pig cardiac cDNA. gpIRK1 is a homologue of the mouse IRK1 channel identified in macrophage cells. Expression of gpIRK1 in Xenopus oocytes produces inwardly rectifying K+ current, similar to the cardiac inward rectifier current IK1. This current is blocked by external Ba2+ and Cs+. Plasmids containing the gpIRK1 coding region under the transcriptional control of constitutive (PGK) or inducible (GAL) promoters were constructed for expression in Saccharomyces cerevisiae. Several observations suggest that gpIRK1 forms functional ion channels when expressed in yeast. gpIRK1 complements a trk1 delta trk2 delta strain, which is defective in potassium uptake. Expression of gpIRK1 in this mutant restores growth on low potassium media. Growth dependent on gpIRK1 is inhibited by external Cs+. The strain expressing gpIRK1 provides a versatile genetic system for studying the assembly and composition of inwardly rectifying K+ channels.

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Effects of Na+ and K+ channel blockade on vulnerability to and termination of fibrillation in simulated normal cardiac tissue

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00241.2005 ◽

2005 ◽

Vol 289 (4) ◽

pp. H1692-H1701 ◽

Cited By ~ 29

Author(s):

Zhilin Qu ◽

James N. Weiss

Keyword(s):

Action Potential ◽

Cardiac Tissue ◽

Theoretical Perspective ◽

Conduction Block ◽

Dynamical Instability ◽

K Channel ◽

Channel Blockade ◽

Wave Instability ◽

Transient Time ◽

Underlying Mechanisms

Na+ and K+ channel-blocking drugs have anti- and proarrhythmic effects. Their effects during fibrillation, however, remain poorly understood. We used computer simulation of a two-dimensional (2-D) structurally normal tissue model with phase I of the Luo-Rudy action potential model to study the effects of Na+ and K+ channel blockade on vulnerability to and termination of reentry in simulated multiple-wavelet and mother rotor fibrillation. Our main findings are as follows: 1) Na+ channel blockade decreased, whereas K+ channel blockade increased, the vulnerable window of reentry in heterogeneous 2-D tissue because of opposing effects on dynamical wave instability. 2) Na+ channel blockade increased the cycle length of reentry more than it increased refractoriness. In multiple-wavelet fibrillation, Na+ channel blockade first increased and then decreased the average duration or transient time (<Ts>) of fibrillation. In mother rotor fibrillation, Na+ channel blockade caused peripheral fibrillatory conduction block to resolve and the mother rotor to drift, leading to self-termination or sustained tachycardia. 3) K+ channel blockade increased dynamical instability by steepening action potential duration restitution. In multiple-wavelet fibrillation, this effect shortened <Ts> because of enhanced wave instability. In mother rotor fibrillation, this effect converted mother rotor fibrillation to multiple-wavelet fibrillation, which then could self-terminate. Our findings help illuminate, from a theoretical perspective, the possible underlying mechanisms of termination of different types of fibrillation by antiarrhythmic drugs.

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