scholarly journals Tethered peptide neurotoxins display two blocking mechanisms in the K+ channel pore as do their untethered analogs

2020 ◽  
Vol 6 (10) ◽  
pp. eaaz3439
Author(s):  
Ruiming Zhao ◽  
Hui Dai ◽  
Netanel Mendelman ◽  
Jordan H. Chill ◽  
Steve A. N. Goldstein
Keyword(s):  
Point Mutation ◽  
Voltage Dependence ◽  
Sea Anemone ◽  
K Channel ◽  
Type I ◽  
Channel Blockade ◽  
Channel Pore ◽  
Biophysical Study ◽  
Blocking Mechanisms ◽  
Kv1.3 Channels

We show here that membrane-tethered toxins facilitate the biophysical study of the roles of toxin residues in K+ channel blockade to reveal two blocking mechanisms in the K+ channel pore. The structure of the sea anemone type I (SAK1) toxin HmK is determined by NMR. T-HmK residues are scanned by point mutation to map the toxin surface, and seven residues are identified to be critical to occlusion of the KcsA channel pore. T-HmK–Lys22 is shown to interact with K+ ions traversing the KcsA pore from the cytoplasm conferring voltage dependence on the toxin off rate, a classic mechanism that we observe as well with HmK in solution and for Kv1.3 channels. In contrast, two related SAK1 toxins, Hui1 and ShK, block KcsA and Kv1.3, respectively, via an arginine rather than the canonical lysine, when tethered and as free peptides.

scholarly journals Tethered Peptide Neurotoxins Facilitate Biophysical Study and Reveal Two Voltage-dependent Blocking Mechanisms for SAK1 Toxins in the K+ Channel Pore

2020 ◽  
Vol 118 (3) ◽  
pp. 110a-111a
Author(s):  
Ruiming Zhao ◽  
Hui Dai ◽  
Netanel Mendelman ◽  
Jordan H. Chill ◽  
Steve A. Goldstein
Keyword(s):  
K Channel ◽  
Channel Pore ◽  
Voltage Dependent ◽  
Biophysical Study ◽  
Blocking Mechanisms

scholarly journals Coupled Ion Movement Underlies Rectification in an Inward-Rectifier K+ Channel

1998 ◽  
Vol 112 (2) ◽  
pp. 211-221 ◽  
Author(s):  
Maria Spassova ◽  
Zhe Lu
Keyword(s):  
Voltage Dependence ◽  
Inward Rectifier ◽  
Membrane Voltage ◽  
Equilibrium Potential ◽  
Inward Rectification ◽  
K Channel ◽  
Channel Blockade ◽  
Electrical Field ◽  
K Current ◽  
Internal Pore

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+.

scholarly journals Correlation between Charge Movement and Ionic Current during Slow Inactivation in Shaker K+ Channels

1997 ◽  
Vol 110 (5) ◽  
pp. 579-589 ◽  
Author(s):  
Riccardo Olcese ◽  
Ramón Latorre ◽  
Ligia Toro ◽  
Francisco Bezanilla ◽  
Enrico Stefani
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Ionic Current ◽  
K Channel ◽  
Charge Movement ◽  
Slow Inactivation ◽  
Gating Currents ◽  
Similar Time ◽  
K Channels ◽  
Recovery From Inactivation

Prolonged depolarization induces a slow inactivation process in some K+ channels. We have studied ionic and gating currents during long depolarizations in the mutant Shaker H4-Δ(6–46) K+ channel and in the nonconducting mutant (Shaker H4-Δ(6–46)-W434F). These channels lack the amino terminus that confers the fast (N-type) inactivation (Hoshi, T., W.N. Zagotta, and R.W. Aldrich. 1991. Neuron. 7:547–556). Channels were expressed in oocytes and currents were measured with the cut-open-oocyte and patch-clamp techniques. In both clones, the curves describing the voltage dependence of the charge movement were shifted toward more negative potentials when the holding potential was maintained at depolarized potentials. The evidences that this new voltage dependence of the charge movement in the depolarized condition is associated with the process of slow inactivation are the following: (a) the installation of both the slow inactivation of the ionic current and the inactivation of the charge in response to a sustained 1-min depolarization to 0 mV followed the same time course; and (b) the recovery from inactivation of both ionic and gating currents (induced by repolarizations to −90 mV after a 1-min inactivating pulse at 0 mV) also followed a similar time course. Although prolonged depolarizations induce inactivation of the majority of the channels, a small fraction remains non–slow inactivated. The voltage dependence of this fraction of channels remained unaltered, suggesting that their activation pathway was unmodified by prolonged depolarization. The data could be fitted to a sequential model for Shaker K+ channels (Bezanilla, F., E. Perozo, and E. Stefani. 1994. Biophys. J. 66:1011–1021), with the addition of a series of parallel nonconducting (inactivated) states that become populated during prolonged depolarization. The data suggest that prolonged depolarization modifies the conformation of the voltage sensor and that this change can be associated with the process of slow inactivation.

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

2003 ◽  
Vol 306 (2) ◽  
pp. 388-393 ◽  
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

scholarly journals Effect of ATP-sensitive K+ channel regulators on cystic fibrosis transmembrane conductance regulator chloride currents.

1992 ◽  
Vol 100 (4) ◽  
pp. 573-591 ◽  
Author(s):  
D N Sheppard ◽  
M J Welsh
Keyword(s):  
Cystic Fibrosis ◽  
Voltage Dependence ◽  
K Channel ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
K Channels ◽  
Intracellular Atp ◽  
Cl Channel ◽  
Cl Channels ◽  
Cystic Fibrosis Transmembrane

The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl- channel that is regulated by cAMP-dependent phosphorylation and by intracellular ATP. Intracellular ATP also regulates a class of K+ channels that have a distinct pharmacology: they are inhibited by sulfonylureas and activated by a novel class of drugs called K+ channel openers. In search of modulators of CFTR Cl- channels, we examined the effect of sulfonylureas and K+ channel openers on CFTR Cl- currents in cells expressing recombinant CFTR. The sulfonylureas, tolbutamide and glibenclamide, inhibited whole-cell CFTR Cl- currents at half-maximal concentrations of approximately 150 and 20 microM, respectively. Inhibition by both agents showed little voltage dependence and developed slowly; > 90% inhibition occurred 3 min after adding 1 mM tolbutamide or 100 microM glibenclamide. The effect of tolbutamide was reversible, while that of glibenclamide was not. In contrast to their activating effect on K+ channels, the K+ channel openers, diazoxide, BRL 38227, and minoxidil sulfate inhibited CFTR Cl- currents. Half-maximal inhibition was observed at approximately 250 microM diazoxide, 50 microM BRL 38227, and 40 microM minoxidil sulfate. The rank order of potency for inhibition of CFTR Cl- currents was: glibenclamide < BRL 38227 approximately equal to minoxidil sulfate > tolbutamide > diazoxide. Site-directed mutations of CFTR in the first membrane-spanning domain and second nucleotide-binding domain did not affect glibenclamide inhibition of CFTR Cl- currents. However, when part of the R domain was deleted, glibenclamide inhibition showed significant voltage dependence. These agents, especially glibenclamide, which was the most potent, may be of value in identifying CFTR Cl- channels. They or related analogues might also prove to be of value in treating diseases such as diarrhea, which may involve increased activity of the CFTR Cl- channel.

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

2005 ◽  
Vol 289 (4) ◽  
pp. H1692-H1701 ◽  
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.

Action potential generation in the small intestine of W mutant mice that lack interstitial cells of Cajal

1996 ◽  
Vol 271 (3) ◽  
pp. G387-G399 ◽  
Author(s):  
J. Malysz ◽  
L. Thuneberg ◽  
H. B. Mikkelsen ◽  
J. D. Huizinga
Keyword(s):  
Small Intestine ◽  
Action Potentials ◽  
Interstitial Cells Of Cajal ◽  
Interstitial Cells ◽  
K Channel ◽  
Pacemaker Activity ◽  
Channel Blockade ◽  
Auerbach’S Plexus ◽  
Cells Of Cajal ◽  
Auerbach's Plexus

The small intestine of W/Wv mice lacks both the network of interstitial cells of Cajal (ICC), associated with Auerbach's plexus, and pacemaker activity, i.e., it does not generate slow-wave-type action potentials. The W/Wv muscle preparations showed a wide variety of electrical activities, ranging from total quiescence to generation of action potentials at regular or irregular frequency with or without periods of quiescence. The action potentials consisted of a slow component with superimposed spikes, preceded by a slowly developing depolarization and followed by a transient hyperpolarization. The action potentials were completely abolished by L-type Ca2+ channel blockers. W/Wv mice responded to K+ channel blockade (0.5 mM Ba2+ or 10 mM tetraethylammonium chloride) with effects on amplitude, frequency, rate of rise, and duration of the action potentials. In quiescent tissues from W/Wv mice, K+ channel blockade evoked the typical spikelike action potentials. Electron microscopy identified few methylene blue-positive cells in the W/Wv small intestine associated with Auerbach's plexus as individual ICC. Numbers of resident macrophage-like cells (MLC) and fibroblast-like cells (FLC) were significantly changed. Neither FLC nor MLC were part of a network nor did they form specialized junctions with neighboring cells as ICC do. Hence no cell type had replaced ICC at their normal morphological position associated with Auerbach's plexus. ICC were present in W/Wv mice at the deep muscular plexus in normal organization and numbers, indicating that they are not dependent on the Kit protein and do not take part in generation of pacemaker activity.

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