scholarly journals Na+ Block and Permeation in a K+ Channel of Known Structure

2002 ◽  
Vol 120 (3) ◽  
pp. 323-335 ◽  
Author(s):  
Crina M. Nimigean ◽  
Christopher Miller
Keyword(s):  
High Voltage ◽  
Voltage Dependence ◽  
Low Voltage ◽  
Selectivity Filter ◽  
K Channel ◽  
Voltage Dependent

The effects of intracellular Na+ were studied on K+ and Rb+ currents through single KcsA channels. At low voltage, Na+ produces voltage-dependent block, which becomes relieved at high voltage by a “punchthrough” mechanism representing Na+ escaping from its blocking site through the selectivity filter. The Na+ blocking site is located in the wide, hydrated vestibule, and it displays unexpected selectivity for K+ and Rb+ against Na+. The voltage dependence of Na+ block reflects coordinated movements of the blocker with permeant ions in the selectivity filter.

scholarly journals Mechanism of the Voltage Sensitivity of IRK1 Inward-rectifier K+ Channel Block by the Polyamine Spermine

2005 ◽  
Vol 125 (4) ◽  
pp. 413-426 ◽  
Author(s):  
Hyeon-Gyu Shin ◽  
Zhe Lu
Keyword(s):  
Steady State ◽  
Voltage Dependence ◽  
Ion Selectivity ◽  
Inward Rectifier ◽  
Selectivity Filter ◽  
K Channel ◽  
Voltage Sensitivity ◽  
Channel Block ◽  
Head Groups ◽  
Voltage Dependent

IRK1 (Kir2.1) inward-rectifier K+ channels exhibit exceedingly steep rectification, which reflects strong voltage dependence of channel block by intracellular cations such as the polyamine spermine. On the basis of studies of IRK1 block by various amine blockers, it was proposed that the observed voltage dependence (valence ∼5) of IRK1 block by spermine results primarily from K+ ions, not spermine itself, traversing the transmembrane electrical field that drops mostly across the narrow ion selectivity filter, as spermine and K+ ions displace one another during channel block and unblock. If indeed spermine itself only rarely penetrates deep into the ion selectivity filter, then a long blocker with head groups much wider than the selectivity filter should exhibit comparably strong voltage dependence. We confirm here that channel block by two molecules of comparable length, decane-bis-trimethylammonium (bis-QAC10) and spermine, exhibit practically identical overall voltage dependence even though the head groups of the former are much wider (∼6 Å) than the ion selectivity filter (∼3 Å). For both blockers, the overall equilibrium dissociation constant differs from the ratio of apparent rate constants of channel unblock and block. Also, although steady-state IRK1 block by both cations is strongly voltage dependent, their apparent channel-blocking rate constant exhibits minimal voltage dependence, which suggests that the pore becomes blocked as soon as the blocker encounters the innermost K+ ion. These findings strongly suggest the existence of at least two (potentially identifiable) sequentially related blocked states with increasing numbers of K+ ions displaced. Consequently, the steady-state voltage dependence of IRK1 block by spermine or bis-QAC10 should increase with membrane depolarization, a prediction indeed observed. Further kinetic analysis identifies two blocked states, and shows that most of the observed steady-state voltage dependence is associated with the transition between blocked states, consistent with the view that the mutual displacement of blocker and K+ ions must occur mainly as the blocker travels along the long inner pore.

Characterization of voltage-dependent calcium currents in mouse motoneurons

1992 ◽  
Vol 68 (1) ◽  
pp. 85-92 ◽  
Author(s):  
M. Mynlieff ◽  
K. G. Beam
Keyword(s):  
Voltage Dependence ◽  
Low Voltage ◽  
Calcium Currents ◽  
Patch Clamp Technique ◽  
Maximal Amplitude ◽  
Time To Peak ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Channel Currents

1. Calcium channel currents were measured with the whole-cell patch clamp technique in cultured, identified mouse motoneurons. Three components of current were operationally defined on the basis of voltage dependence, kinetics, and pharmacology. 2. Test potentials to -50 mV or greater (10 mM external Ca2+) elicited a low-voltage activated T-type current that was transient (decaying to baseline in less than 200 ms) and had a relatively slow time to peak (20-50 ms). A 1-s prepulse to -45 mV produced approximately half-maximal inactivation of this T current. 3. Two high-voltage activated (HVA) components of current (1 transient and 1 sustained) were activated by test potentials to -20 mV or greater (10 mM external Ca2+). A 1-s prepulse to -35 mV produced approximately half-maximal inactivation of the transient component without affecting the sustained component. 4. When Ba2+ was substituted for Ca2+ as the charge carrier, activation of the HVA components was shifted in the hyperpolarizing direction, and the relative amplitude of the transient HVA component was reduced. 5. Amiloride (1-2 mM) caused a reversible, partial block of the T current without affecting the HVA components. 6. The dihydropyridine agonist isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridine-carboxylate [(+)-SDZ 202-791, 100 nM-1 microM)] shifted the activation of the sustained component of HVA current to more negative potentials and increased its maximal amplitude. Additionally, (+)-SDZ 202-791 caused the appearance of a slowed component of tail current.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Voltage-gated calcium channels in GtoPdb v.2021.2

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
William A. Catterall ◽  
Edward Perez-Reyes ◽  
Terrance P. Snutch ◽  
Jörg Striessnig
Keyword(s):  
High Voltage ◽  
Low Voltage ◽  
Transmembrane Domains ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Alternatively Spliced ◽  
Membrane Spanning ◽  
Voltage Gated Ion Channels ◽  
Ca2 Channels ◽  
Α1 Subunit

Calcium (Ca2+) channels are voltage-gated ion channels present in the membrane of most excitable cells. The nomenclature for Ca2+channels was proposed by [127] and approved by the NC-IUPHAR Subcommittee on Ca2+ channels [70]. Most Ca2+ channels form hetero-oligomeric complexes. The α1 subunit is pore-forming and provides the binding site(s) for practically all agonists and antagonists. The 10 cloned α1-subunits can be grouped into three families: (1) the high-voltage activated dihydropyridine-sensitive (L-type, CaV1.x) channels; (2) the high- to moderate-voltage activated dihydropyridine-insensitive (CaV2.x) channels and (3) the low-voltage-activated (T-type, CaV3.x) channels. Each α1 subunit has four homologous repeats (I-IV), each repeat having six transmembrane domains and a pore-forming region between transmembrane domains S5 and S6. Voltage-dependent gating is driven by the membrane spanning S4 segment, which contains highly conserved positive charges that respond to changes in membrane potential. All of the α1-subunit genes give rise to alternatively spliced products. At least for high-voltage activated channels, it is likely that native channels comprise co-assemblies of α1, β and α2-δ subunits. The γ subunits have not been proven to associate with channels other than the α1s skeletal muscle Cav1.1 channel. The α2-δ1 and α2-δ2 subunits bind gabapentin and pregabalin.

scholarly journals Structure of a pore-blocking toxin in complex with a eukaryotic voltage-dependent K+ channel

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Anirban Banerjee ◽  
Alice Lee ◽  
Ernest Campbell ◽  
Roderick MacKinnon
Keyword(s):  
Electron Density ◽  
Selectivity Filter ◽  
K Channel ◽  
Wild Type ◽  
Kv Channel ◽  
Pore Blocking ◽  
Kv Channels ◽  
Filter Structure ◽  
Conduction Pathway ◽  
Voltage Dependent

Pore-blocking toxins inhibit voltage-dependent K+ channels (Kv channels) by plugging the ion-conduction pathway. We have solved the crystal structure of paddle chimera, a Kv channel in complex with charybdotoxin (CTX), a pore-blocking toxin. The toxin binds to the extracellular pore entryway without producing discernable alteration of the selectivity filter structure and is oriented to project its Lys27 into the pore. The most extracellular K+ binding site (S1) is devoid of K+ electron-density when wild-type CTX is bound, but K+ density is present to some extent in a Lys27Met mutant. In crystals with Cs+ replacing K+, S1 electron-density is present even in the presence of Lys27, a finding compatible with the differential effects of Cs+ vs K+ on CTX affinity for the channel. Together, these results show that CTX binds to a K+ channel in a lock and key manner and interacts directly with conducting ions inside the selectivity filter.

scholarly journals Selectivity filter instability dominates the low intrinsic activity of the TWIK-1 K2P K+ channel

2019 ◽  
Vol 295 (2) ◽  
pp. 610-618
Author(s):  
Ehsan Nematian-Ardestani ◽  
Firdaus Abd-Wahab ◽  
Franck C. Chatelain ◽  
Han Sun ◽  
Marcus Schewe ◽  
...  
Keyword(s):  
Functional Activity ◽  
Selectivity Filter ◽  
Intrinsic Activity ◽  
K Channel ◽  
Open Probability ◽  
Gating Mechanism ◽  
Hydrophobic Barrier ◽  
K2p Channels ◽  
Voltage Dependent ◽  
Low Levels

Two-pore domain K+ (K2P) channels have many important physiological functions. However, the functional properties of the TWIK-1 (K2P1.1/KCNK1) K2P channel remain poorly characterized because heterologous expression of this ion channel yields only very low levels of functional activity. Several underlying reasons have been proposed, including TWIK-1 retention in intracellular organelles, inhibition by posttranslational sumoylation, a hydrophobic barrier within the pore, and a low open probability of the selectivity filter (SF) gate. By evaluating these potential mechanisms, we found that the latter dominates the low intrinsic functional activity of TWIK-1. Investigating this further, we observed that the low activity of the SF gate appears to arise from the inefficiency of K+ in stabilizing an active (i.e. conductive) SF conformation. In contrast, other permeant ion species, such as Rb+, NH4+, and Cs+, strongly promoted a pH-dependent activated conformation. Furthermore, many K2P channels are activated by membrane depolarization via an SF-mediated gating mechanism, but we found here that only very strong nonphysiological depolarization produces voltage-dependent activation of heterologously expressed TWIK-1. Remarkably, we also observed that TWIK-1 Rb+ currents are potently inhibited by intracellular K+ (IC50 = 2.8 mm). We conclude that TWIK-1 displays unique SF gating properties among the family of K2P channels. In particular, the apparent instability of the conductive conformation of the TWIK-1 SF in the presence of K+ appears to dominate the low levels of intrinsic functional activity observed when the channel is expressed at the cell surface.

scholarly journals A scheme to account for the effects of Rb+ and K+ on inward rectifier K channels of bovine artery endothelial cells.

1994 ◽  
Vol 103 (4) ◽  
pp. 549-581 ◽  
Author(s):  
P S Pennefather ◽  
T E DeCoursey
Keyword(s):  
Binding Sites ◽  
Voltage Dependence ◽  
Reversal Potential ◽  
Companion Paper ◽  
K Channel ◽  
Gating Model ◽  
Allosteric Sites ◽  
Voltage Dependent ◽  
Cooperative Process ◽  
Activator Ions

An electrochemical gating model is presented to account for the effects described in the companion paper by M. R. Silver, M. S. Shapiro, and T. E. DeCoursey (1994. Journal of General Physiology, 103:519-548) of Rb+ and Rb+/K+ mixtures on the kinetics and voltage dependence of an inwardly rectifying (IR) K+ channel. The model proposes that both Rb+ and K+ act as allosteric modulators of an intrinsically voltage dependent isomerization between open and closed states. Occupancy of binding sites on the outside of the channel promotes channel opening and stabilizes the open state. Rb+ binds to separate sites within the pore and plugs IR channels. Occupancy of the pore by Rb+ can modify the rates of isomerization and the affinity of the allosteric sites for activator ions. The model also incorporates the proposed triple-barreled nature of the IR channel (Matsuda, H., 1988. Journal of Physiology. 397:237-258.) by proposing that plugging of the channel is a cooperative process involving a single site in each of the three bores, 80% of the way through the membrane field. Interaction between bores during plugging and permeation is consistent with correlated flux models of the properties of the IR channel. Parallel bores multiply the number allosteric sites associated with the macromolecular channel and allow for steep voltage dependence without compromising the parallel shift of the half-activation potential with reversal potential. Our model proposes at least six and possibly 12 such allosteric binding sites for activator ions. We derive algebraic relations that permit derivation of parameters that define simple versions of our model from the data of Silver et al. (1994). Numerical simulations based on those parameters closely reproduce that data. The model reproduces the RS+ induced slowing of IR kinetics and the negative shift of the relation between the half-activation voltage (V1/2) and reversal potential when channel plugging is associated with (a) a slowing of the isomerization rates; (b) an increase in the affinity of allosteric sites on closed channels that promote opening; and (c) a decrease in the affinity of sites on open channels that slow closing. Rb+ also slows closing at positive potentials where open channel blockade is unlikely. Allowing Rb+ to be 1.5 times more potent than K+ as an activator in the model can account for this effect and improves the match between the predicted and observed relation between the Rb+ to K+ mole fraction and the opening rate at V1/2.(ABSTRACT TRUNCATED AT 400 WORDS)

The Research of Capacitive Load Influence on Inductive Voltage Divider

2013 ◽  
Vol 718-720 ◽  
pp. 1537-1541
Author(s):  
Yan Qiang Li ◽  
Wen Feng Li ◽  
Hai Ming Shao ◽  
Fei Peng Lin ◽  
Bo Liang ◽  
...  
Keyword(s):  
High Voltage ◽  
Voltage Dependence ◽  
Low Voltage ◽  
Analytical Formula ◽  
Voltage Divider ◽  
Model Analysis ◽  
Circuit Model ◽  
Capacitive Load ◽  
In Series ◽  
Inductive Voltage Divider

The inductive voltage divider is usually used and calibrated at no-load situation, but it also used at taking load situation. For example in the situation of measuring voltage dependence of low voltage capacitors and detecting high voltage bridge, the inductive voltage divider need to take two specific capacitors. This paper have researched the influence of specific capacitive load on its ratio and deduced the analytical formula through related experiments and circuit model analysis when it takes capacitor. And use the method of connecting resistor in series to compensate its ratio accuracy to 1×10-6 degree.

scholarly journals Evidence for Sequential Ion-binding Loci along the Inner Pore of the IRK1 Inward-rectifier K+ Channel

2005 ◽  
Vol 126 (2) ◽  
pp. 123-135 ◽  
Author(s):  
Hyeon-Gyu Shin ◽  
Yanping Xu ◽  
Zhe Lu
Keyword(s):  
Voltage Dependence ◽  
Inward Rectifier ◽  
Selectivity Filter ◽  
K Channel ◽  
Ion Binding ◽  
Side Chains ◽  
Aromatic Side Chain ◽  
Voltage Drops ◽  
Inner Pore ◽  
Aromatic Side Chains

Steep rectification in IRK1 (Kir2.1) inward-rectifier K+ channels reflects strong voltage dependence (valence of ∼5) of channel block by intracellular cationic blockers such as the polyamine spermine. The observed voltage dependence primarily results from displacement, by spermine, of up to five K+ ions across the narrow K+ selectivity filter, along which the transmembrane voltage drops steeply. Spermine first binds, with modest voltage dependence, at a shallow site where it encounters the innermost K+ ion and impedes conduction. From there, spermine can proceed to a deeper site, displacing several more K+ ions and thereby producing most of the observed voltage dependence. Since in the deeper blocked state the leading amine group of spermine reaches into the cavity region (internal to the selectivity filter) and interacts with residue D172, its trailing end is expected to be near M183. Here, we found that mutation M183A indeed affected the deeper blocked state, which supports the idea that spermine is located in the region lined by the M2 and not deep in the narrow K+ selectivity filter. As to the shallower site whose location has been unknown, we note that in the crystal structure of homologous GIRK1 (Kir3.1), four aromatic side chains of F255, one from each of the four subunits, constrict the intracellular end of the pore to ∼10 Å. For technical simplicity, we used tetraethylammonium (TEA) as an initial probe to test whether the corresponding residue in IRK1, F254, forms the shallower site. We found that replacing the aromatic side chain with an aliphatic one not only lowered TEA affinity of the shallower site ∼100-fold but also eliminated the associated voltage dependence and, furthermore, confirmed that similar effects occurred also for spermine. These results establish the evidence for physically separate, sequential ion-binding loci along the long inner pore of IRK1, and strongly suggest that the aromatic side chains of F254 underlie the likely innermost binding locus for both blocker and K+ ions in the cytoplasmic pore.

scholarly journals Intrinsic versus extrinsic voltage sensitivity of blocker interaction with an ion channel pore

2010 ◽  
Vol 135 (2) ◽  
pp. 149-167 ◽  
Author(s):  
Juan Ramón Martínez-François ◽  
Zhe Lu
Keyword(s):  
Electric Field ◽  
Voltage Dependence ◽  
Ion Selectivity ◽  
Systematic Investigation ◽  
Selectivity Filter ◽  
Voltage Sensitivity ◽  
Channel Block ◽  
Boltzmann Function ◽  
Voltage Dependent ◽  
Gated Channel

Many physiological and synthetic agents act by occluding the ion conduction pore of ion channels. A hallmark of charged blockers is that their apparent affinity for the pore usually varies with membrane voltage. Two models have been proposed to explain this voltage sensitivity. One model assumes that the charged blocker itself directly senses the transmembrane electric field, i.e., that blocker binding is intrinsically voltage dependent. In the alternative model, the blocker does not directly interact with the electric field; instead, blocker binding acquires voltage dependence solely through the concurrent movement of permeant ions across the field. This latter model may better explain voltage dependence of channel block by large organic compounds that are too bulky to fit into the narrow (usually ion-selective) part of the pore where the electric field is steep. To date, no systematic investigation has been performed to distinguish between these voltage-dependent mechanisms of channel block. The most fundamental characteristic of the extrinsic mechanism, i.e., that block can be rendered voltage independent, remains to be established and formally analyzed for the case of organic blockers. Here, we observe that the voltage dependence of block of a cyclic nucleotide–gated channel by a series of intracellular quaternary ammonium blockers, which are too bulky to traverse the narrow ion selectivity filter, gradually vanishes with extreme depolarization, a predicted feature of the extrinsic voltage dependence model. In contrast, the voltage dependence of block by an amine blocker, which has a smaller “diameter” and can therefore penetrate into the selectivity filter, follows a Boltzmann function, a predicted feature of the intrinsic voltage dependence model. Additionally, a blocker generates (at least) two blocked states, which, if related serially, may preclude meaningful application of a commonly used approach for investigating channel gating, namely, inferring the properties of the activation gate from the kinetics of channel block.

scholarly journals Two Stable, Conducting Conformations of the Selectivity Filter in Shaker K+ Channels

2005 ◽  
Vol 125 (6) ◽  
pp. 619-629 ◽  
Author(s):  
Jill Thompson ◽  
Ted Begenisich
Keyword(s):  
Voltage Dependence ◽  
Relative Proportion ◽  
Selectivity Filter ◽  
K Channel ◽  
K Channels ◽  
High Affinity ◽  
K Concentration ◽  
The One ◽  
Low K ◽  
Two Populations

We have examined the voltage dependence of external TEA block of Shaker K+ channels over a range of internal K+ concentrations from 2 to 135 mM. We found that the concentration dependence of external TEA block in low internal K+ solutions could not be described by a single TEA binding affinity. The deviation from a single TEA binding isotherm was increased at more depolarized membrane voltages. The data were well described by a two-component binding scheme representing two, relatively stable populations of conducting channels that differ in their affinity for external TEA. The relative proportion of these two populations was not much affected by membrane voltage but did depend on the internal K+ concentration. Low internal K+ promoted an increase in the fraction of channels with a low TEA affinity. The voltage dependence of the apparent high-affinity TEA binding constant depended on the internal K+ concentration, becoming almost voltage independent in 5 mM. The K+ sensitivity of these low- and high-affinity TEA states suggests that they may represent one- and two-ion occupancy states of the selectivity filter, consistent with recent crystallographic results from the bacterial KcsA K+ channel. We therefore analyzed these data in terms of such a model and found a large (almost 14-fold) difference between the intrinsic TEA affinity of the one-ion and two-ion modes. According to this analysis, the single ion in the one-ion mode (at 0 mV) prefers the inner end of the selectivity filter twofold more than the outer end. This distribution does not change with internal K+. The two ions in the two-ion mode prefer to occupy the inner end of the selectivity filter at low K+, but high internal K+ promotes increased occupancy of the outer sites. Our analysis further suggests that the four K+ sites in the selectivity filter are spaced between 20 and 25% of the membrane electric field.

Sign in / Sign up

Export Citation Format

Share Document