scholarly journals Computational Insights Into Voltage Dependence of Polyamine Block in a Strong Inwardly Rectifying K+ Channel

2020 ◽  
Vol 11 ◽  
Author(s):  
Xingyu Chen ◽  
Michael Bründl ◽  
Theres Friesacher ◽  
Anna Stary-Weinzinger
Keyword(s):  
Voltage Dependence ◽  
K Channel ◽  
Inwardly Rectifying

scholarly journals Permeation and Gating of an Inwardly Rectifying Potassium Channel

1998 ◽  
Vol 112 (4) ◽  
pp. 433-446 ◽  
Author(s):  
Han Choe ◽  
Henry Sackin ◽  
Lawrence G. Palmer
Keyword(s):  
Voltage Dependence ◽  
Divalent Cations ◽  
K Channel ◽  
Single Channels ◽  
Closed State ◽  
Inwardly Rectifying Potassium Channel ◽  
Well Model ◽  
K Concentration ◽  
Inwardly Rectifying ◽  
Kinetics Of

Permeation, gating, and their interrelationship in an inwardly rectifying potassium (K+) channel, ROMK2, were studied using heterologous expression in Xenopus oocytes. Patch-clamp recordings of single channels were obtained in the cell-attached mode. The gating kinetics of ROMK2 were well described by a model having one open and two closed states. One closed state was short lived (∼1 ms) and the other was longer lived (∼40 ms) and less frequent (∼1%). The long closed state was abolished by EDTA, suggesting that it was due to block by divalent cations. These closures exhibit a biphasic voltage dependence, implying that the divalent blockers can permeate the channel. The short closures had a similar biphasic voltage dependence, suggesting that they could be due to block by monovalent, permeating cations. The rate of entering the short closed state varied with the K+ concentration and was proportional to current amplitude, suggesting that permeating K+ ions may be related to the short closures. To explain the results, we propose a variable intrapore energy well model in which a shallow well may change into a deep one, resulting in a normally permeant K+ ion becoming a blocker of its own channel.

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.

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.

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

1995 ◽  
Vol 6 (9) ◽  
pp. 1231-1240 ◽  
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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