scholarly journals Cation permeation through the voltage-dependent potassium channel in the squid axon. Characteristics and mechanisms.

1987 ◽  
Vol 90 (2) ◽  
pp. 261-290 ◽  
Author(s):  
P K Wagoner ◽  
G S Oxford
Keyword(s):  
Binding Energies ◽  
Ion Concentration ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
K Channels ◽  
Energy Profiles ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Ion Binding Sites

Characteristics of cation permeation through voltage-dependent delayed rectifier K channels in squid giant axons were examined. Axial wire voltage-clamp measurements and internal perfusion were used to determine conductance and permeability properties. These K channels exhibit conductance saturation and decline with increases in symmetrical K+ concentrations to 3 M. They also produce ion- and concentration-dependent current-voltage shapes. K channel permeability ratios obtained with substitutions of internal Rb+ or NH+4 for K+ are higher than for external substitution of these ions. Furthermore, conductance and permeability ratios of NH+4 or Rb+ to K+ are functions of ion concentration. Conductance measurements also reveal the presence of an anomalous mole fraction effect for NH+4, Rb+, or Tl+ to K+. Finally, internal Cs+ blocks these K channels in a voltage-dependent manner, with relief of block by elevations in external K+ but not external NH+4 or Cs+. Energy profiles for K+, NH+4, Rb+, Tl+, and Cs+ incorporating three barriers and two ion-binding sites are fitted to the data. The profiles are asymmetric with respect to the center of the electric field, have different binding energies and electrical positions for each ion, and (for K+) exhibit concentration-dependent barrier positions.

Ba2+, TEA+, and quinine effects on apical membrane K+ conductance and maxi K+ channels in gallbladder epithelium

1990 ◽  
Vol 259 (1) ◽  
pp. C56-C68 ◽  
Author(s):  
Y. Segal ◽  
L. Reuss
Keyword(s):  
Apical Membrane ◽  
Membrane Conductance ◽  
Membrane Resistance ◽  
K Channel ◽  
Dependent Manner ◽  
Gallbladder Epithelium ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Voltage Dependent ◽  
Channel Currents

The apical membrane of Necturus gallbladder epithelium contains a voltage-activated K+ conductance [Ga(V)]. Large-conductance (maxi) K+ channels underlie Ga(V) and account for 17% of the membrane conductance (Ga) under control conditions. We examined the Ba2+, tetraethylammonium (TEA+), and quinine sensitivities of Ga and single maxi K+ channels. Mucosal Ba2+ addition decreased resting Ga in a concentration-dependent manner (65% block at 5 mM) and decreased Ga(V) in a concentration- and voltage-dependent manner. Mucosal TEA+ addition also decreased control Ga (60% reduction at 5 mM). TEA+ block of Ga(V) was more potent and less voltage dependent that Ba2+ block. Maxi K+ channels were blocked by external Ba2+ at millimolar levels and by external TEA+ at submillimolar levels. At 0.3 mM, quinine (mucosal addition) hyperpolarized the cell membranes by 6 mV and reduced the fractional apical membrane resistance by 50%, suggesting activation of an apical membrane K+ conductance. At 1 mM, quinine both activated and blocked K(+)-conductive pathways. Quinine blocked maxi K+ channel currents at submillimolar concentrations. We conclude that 1) Ba2+ and TEA+ block maxi K+ channels and other K+ channels underlying resting Ga; 2) parallels between the Ba2+ and TEA+ sensitivities of Ga(V) and maxi K+ channels support a role for these channels in Ga(V); and 3) quinine has multiple effects on K(+)-conductive pathways in gallbladder epithelium, which are only partially explained by block of apical membrane maxi K+ channels.

scholarly journals Charybdotoxin selectively blocks small Ca-activated K channels in Aplysia neurons.

1987 ◽  
Vol 90 (1) ◽  
pp. 27-47 ◽  
Author(s):  
A Hermann ◽  
C Erxleben
Keyword(s):  
Single Channel ◽  
Delayed Rectifier ◽  
Pacemaker Activity ◽  
Dependent Manner ◽  
Open Probability ◽  
Apparent Dissociation Constant ◽  
External Application ◽  
K Channels ◽  
Voltage Dependent ◽  
K Current

The action of charybdotoxin (ChTX), a peptide component isolated from the venom of the scorpion Leiurus quinquestriatus, was investigated on membrane currents of identified neurons from the marine mollusk, Aplysia californica. Macroscopic current recordings showed that the external application of ChTX blocks the Ca-activated K current in a dose- and voltage-dependent manner. The apparent dissociation constant is 30 nM at V = -30 mV and increases e-fold for a +50- to +70-mV change in membrane potential, which indicates that the toxin molecule is sensitive to approximately 35% of the transmembrane electric field. The toxin is bound to the receptor with a 1:1 stoichiometry and its effect is reversible after washout. The toxin also suppresses the membrane leakage conductance and a resting K conductance activated by internal Ca ions. The toxin has no significant effect on the inward Na or Ca currents, the transient K current, or the delayed rectifier K current. Records from Ca-activated K channels revealed a single channel conductance of 35 +/- 5 pS at V = 0 mV in asymmetrical K solution. The channel open probability increased with the internal Ca concentration and with membrane voltage. The K channels were blocked by submillimolar concentrations of tetraethylammonium ions and by nanomolar concentrations of ChTX, but were not blocked by 4-aminopyridine if applied externally on outside-out patches. From the effects of ChTX on K current and on bursting pacemaker activity, it is concluded that the termination of bursts is in part controlled by a Ca-activated K conductance.

scholarly journals Fast inactivation causes rectification of the IKr channel.

1996 ◽  
Vol 107 (5) ◽  
pp. 611-619 ◽  
Author(s):  
P S Spector ◽  
M E Curran ◽  
A Zou ◽  
M T Keating ◽  
M C Sanguinetti
Keyword(s):  
Outward Current ◽  
K Channel ◽  
Delayed Rectifier ◽  
Fast Inactivation ◽  
Time Constants ◽  
Recovery From Inactivation ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Cardiac Delayed Rectifier ◽  
Cytoplasmic Side

The mechanism of rectification of HERG, the human cardiac delayed rectifier K+ channel, was studied after heterologous expression in Xenopus oocytes. Currents were measured using two-microelectrode and macropatch voltage clamp techniques. The fully activated current-voltage (I-V) relationship for HERG inwardly rectified. Rectification was not altered by exposing the cytoplasmic side of a macropatch to a divalent-free solution, indicating this property was not caused by voltage-dependent block of outward current by Mg2+ or other soluble cytosolic molecules. The instantaneous I-V relationship for HERG was linear after removal of fast inactivation by a brief hyperpolarization. The time constants for the onset of and recovery from inactivation were a bell-shaped function of membrane potential. The time constants of inactivation varied from 1.8 ms at +50 mV to 16 ms at -20 mV; recovery from inactivation varied from 4.7 ms at -120 mV to 15 ms at -50 mV. Truncation of the NH2-terminal region of HERG shifted the voltage dependence of activation and inactivation by +20 to +30 mV. In addition, the rate of deactivation of the truncated channel was much faster than wild-type HERG. The mechanism of HERG rectification is voltage-gated fast inactivation. Inactivation of channels proceeds at a much faster rate than activation, such that no outward current is observed upon depolarization to very high membrane potentials. Fast inactivation of HERG and the resulting rectification are partly responsible for the prolonged plateau phase typical of ventricular action potentials.

scholarly journals Permeation, selectivity, and blockade of the Ca2+-activated potassium channel of the guinea pig taenia coli myocyte.

1989 ◽  
Vol 94 (5) ◽  
pp. 849-862 ◽  
Author(s):  
S L Hu ◽  
Y Yamamoto ◽  
C Y Kao
Keyword(s):  
Guinea Pig ◽  
Action Potential ◽  
Single Channel ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Taenia Coli ◽  
Excitable Membranes ◽  
Voltage Dependent ◽  
Permeation Properties

The permeation properties of the 147-pS Ca2+-activated K+ channel of the taenia coli myocytes are similar to those of the delayed rectifier channel in other excitable membranes. It has a selectivity sequence of K+ 1.0 greater than Rb+ 0.65 greater than NH4+ 0.50. Na+, Cs+, Li+, and TEA+ (tetraethylammonium) are impermeant. Internal Na+ blocks K+ channel in a strongly voltage-dependent manner with an equivalent valence (zd) of 1.20. Blockade by internal Cs+ and TEA+ is less voltage dependent, with d of 0.61 and 0.13, and half-blockage concentrations of 88 and 31 mM, respectively. External TEA+ is about 100 times more effective in blocking the K+ channel. All these findings suggest that the 147-pS Ca2+-activated K+ channel in the taenia myocytes, which functions physiologically like the delayed rectifier, is the single-channel basis of the repolarizing current in an action potential.

scholarly journals Dynamics of aminopyridine block of potassium channels in squid axon membrane.

1976 ◽  
Vol 68 (5) ◽  
pp. 519-535 ◽  
Author(s):  
J Z Yeh ◽  
G S Oxford ◽  
C H Wu ◽  
T Narahashi
Keyword(s):  
Time Course ◽  
Membrane Surface ◽  
K Channel ◽  
Dependent Manner ◽  
Squid Axon ◽  
Axon Membrane ◽  
K Channels ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Aminopyridines (2-AP, 3-AP, and 4-AP) selectively block K channels of squid axon membranes in a manner dependent upon the membrane potential and the duration and frequency of voltage clamp pulses. They are effective when applied to either the internal or the external membrane surface. The steady-state block of K channels by aminopyridines is more complete for low depolarizations, and is gradually relieved at higher depolarizations. The K current in the presence of aminopyridines rises more slowly than in control, the change being more conspicuous in 3-AP and 4-AP than in 2-AP. Repetitive pulsing relieves the block in a manner dependent upon the duration and interval of pulses. The recovery from block during a given test pulse is enhanced by increasing the duration of a conditioning depolarizing prepulse. The time constant for this recovery is in the range of 10-20 ms in 3-AP and 4-AP, and shorter in 2-AP. Twin pulse experiments with variable pulse intervals have revealed that the time course for re-establishment of block is much slower in 3-AP and 4-AP than in 2-AP. These results suggest that 2-AP interacts with the K channel more rapidly than 3-AP and 4-AP. The more rapid interaction of 2-AP with K channels is reflected in the kinetics of K current which is faster than that observed in 3-AP or 4-AP, and in the pattern of frequency-dependent block which is different from that in 3-AP or 4-AP. The experimental observations are not satisfactorily described by alterations of Hodgkin-Huxley n-type gating units. Rather, the data are consistent with a simple binding scheme incorporating no changes in gating kinetics which conceives of aminopyridine molecules binding to closed K channels and being released from open channels in a voltage-dependent manner.

scholarly journals AKT2/3 Subunits Render Guard Cell K+ Channels Ca2+ Sensitive

2005 ◽  
Vol 125 (5) ◽  
pp. 483-492 ◽  
Author(s):  
Natalya Ivashikina ◽  
Rosalia Deeken ◽  
Susanne Fischer ◽  
Peter Ache ◽  
Rainer Hedrich
Keyword(s):  
Guard Cell ◽  
Guard Cells ◽  
Inward Rectifier ◽  
Hek293 Cells ◽  
K Channel ◽  
Dependent Manner ◽  
Wild Type ◽  
K Channels ◽  
Isolation And Characterization ◽  
Voltage Dependent

Inward-rectifying K+ channels serve as a major pathway for Ca2+-sensitive K+ influx into guard cells. Arabidopsis thaliana guard cell inward-rectifying K+ channels are assembled from multiple K+ channel subunits. Following the recent isolation and characterization of an akt2/3-1 knockout mutant, we examined whether the AKT2/3 subunit carries the Ca2+ sensitivity of the guard cell inward rectifier. Quantification of RT-PCR products showed that despite the absence of AKT2 transcripts in guard cells of the knockout plant, expression levels of the other K+ channel subunits (KAT1, KAT2, AKT1, and AtKC1) remained largely unaffected. Patch-clamp experiments with guard cell protoplasts from wild type and akt2/3-1 mutant, however, revealed pronounced differences in Ca2+ sensitivity of the K+ inward rectifier. Wild-type channels were blocked by extracellular Ca2+ in a concentration- and voltage-dependent manner. Akt2/3-1 mutants lacked the voltage-dependent Ca2+ block, characteristic for the K+ inward rectifier. To confirm the akt2/3-1 phenotype, two independent knockout mutants, akt2-1 and akt2::En-1 were tested, demonstrating that the loss of AKT2/3 indeed affects the Ca2+ dependence of guard cell inward rectifier. In contrast to AKT2 knockout plants, AKT1, AtKC1, and KAT1 loss-of-function mutants retained Ca2+ block of the guard cell inward rectifier. When expressed in HEK293 cells, AKT2 channel displayed a pronounced susceptibility toward extracellular Ca2+, while the dominant guard cell K+ channel KAT2 was Ca2+ insensitive. Thus, we conclude that the AKT2/3 subunit constitutes the Ca2+ sensitivity of the guard cell K+ uptake channel.

A novel approach allows identification of K channels in the lateral membrane of rat CCD

1994 ◽  
Vol 266 (5) ◽  
pp. F813-F822 ◽  
Author(s):  
W. H. Wang ◽  
C. M. McNicholas ◽  
A. S. Segal ◽  
G. Giebisch
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Cell Membrane Potential ◽  
K Channel ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Lateral Membrane ◽  
Novel Approach ◽  
Voltage Dependent

We have developed a novel approach to study K channels in the lateral membrane of principal cells (PC) in rat cortical collecting ducts (CCD). The technique consists of 1) exposing the CCD apical membrane, 2) removing the intercalated cells adjoining a PC by gentle suction through a pipette, and 3) applying patch-clamp technique to the lateral membrane of PC. Functional viability of the PC was confirmed by three indexes: 1) maintenance of physiological cell membrane potentials (-85 +/- 3 mV); 2) depolarization of the cell membrane potential with 1 mM Ba2+; and 3) hyperpolarization of the cell potential with 0.1 mM amiloride. Two types of K channels were identified: a low-conductance K channel and an intermediate-conductance K channel. In cell-attached patches the slope conductance of the low-conductance K channel was 27 pS and that of the intermediate-conductance K channel was 45 pS. The open probability (Po) of the 27-pS K channel was 0.81 +/- 0.02 and was not voltage dependent. In contrast, the Po of the 45-pS K channel was 0.23 +/- 0.01 at the spontaneous cell membrane potential and was increased by hyperpolarization. In addition, decrease of the bath pH from 7.4 to 6.7 reduced the 27-pS K channel current amplitude in a voltage-dependent manner, but the Po was not affected. Finally, two time constants were required to fit open- and closed-time histograms of both populations of K channels. Application of 1 mM Ba2+ completely blocked these K channels. We conclude that two types of K channel are present in the basolateral membrane of PC.

Ca-activated K channels in apical membrane of mammalian CCT, and their role in K secretion

1987 ◽  
Vol 252 (3) ◽  
pp. F458-F467 ◽  
Author(s):  
G. Frindt ◽  
L. G. Palmer
Keyword(s):  
Apical Membrane ◽  
K Channel ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Voltage Dependent ◽  
K Secretion ◽  
Excised Patches ◽  
Cytoplasmic Side ◽  
High Conductance

High conductance, Ca-activated K channels were studied in the apical membrane of the rat cortical collecting tubule (CCT) using the patch-clamp technique. In cell-attached patches the channels were found mainly in the closed state at the spontaneous apical membrane potential. They spent progressively more time in the open state as the pipette potential was made negative relative to the bath. In excised patches these channels had a high selectivity for K over Na and were activated by micromolar concentrations of Ca2+ on the cytoplasmic side of the membrane in a voltage-dependent manner. They had a low conductance to Rb and were blocked by Ba (1-100 microM) from the cytoplasmic side and tetraethylammonium (TEA) (0.2-1 mM) from the luminal side. Block by external TEA and small conductance to Rb were used to investigate the role of these channels in K transport by the isolated perfused rabbit CCT. Ba (2.5 mM), a well-studied blocker of apical K conductance in this segment, hyperpolarized the transepithelial voltage (VT) by 3.7 +/- 0.9 mV when added to the luminal solution of the perfused tubule. Addition of TEA (5 mM) to the luminal solution has no effect on VT. When Na transport was abolished by luminal amiloride, perfusion with 30 mM K (replacing Na) resulted in a lumen-negative VT (18-34 mV). Under these conditions, VT was reduced by 6.0 +/- 1.5 mV by 2.5 mM Ba, whereas TEA had no effect. Perfusion with 30 mM Rb (replacing Na) also caused a lumen-negative VT that was approximately 50% of that observed with 30 mM K. The apical K conductance of the perfused CCT appears to be insensitive to luminal TEA and only modestly selective for K over Rb. This conductance, at least under the conditions of our studies, is probably not mediated by the high conductance Ca-activated K channel.

scholarly journals Actions of FTY720 (Fingolimod), a Sphingosine-1-Phosphate Receptor Modulator, on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-Lymphocytes

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4525
Author(s):  
Wei-Ting Chang ◽  
Ping-Yen Liu ◽  
Sheng-Nan Wu
Keyword(s):  
T Lymphocytes ◽  
Immune Cells ◽  
K Channel ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Dependent Manner ◽  
Inactivation Curve ◽  
K Channels ◽  
Sphingosine 1 Phosphate ◽  
K Current

FTY720 (fingolimod), a modulator of sphingosine-1-phosphate receptors, is known to produce the immunomodulatory actions and to be beneficial for treating the relapsing multiple sclerosis. However, whether it exerts any effects on membrane ion currents in immune cells remains largely unknown. Herein, the effects of FTY720 on ionic currents in Jurkat T-lymphocytes were investigated. Cell exposure to FTY720 suppressed the amplitude of delayed-rectifier K+ current (IK(DR)) in a time- and concentration-dependent manner with an IC50 value of 1.51 μM. Increasing the FTY720 concentration not only decreased the IK(DR) amplitude but also accelerated the inactivation time course of the current. By using the minimal reaction scheme, the effect of FTY720 on IK(DR) inactivation was estimated with a dissociation constant of 3.14 μM. FTY720 also shifted the inactivation curve of IK(DR) to a hyperpolarized potential with no change in the slope factor, and recovery from IK(DR) became slow during the exposure to this compound. Cumulative inactivation for IK(DR) in response to repetitive depolarizations was enhanced in the presence of FTY720. In SEW2871-treated cells, FTY720-induced inhibition of IK(DR) was attenuated. This compound also exerted a stimulatory action on the activity of intermediate-conductance Ca2+-activated K+ channels in Jurkat T-lymphocytes. However, in NSC-34 neuronal cells, FTY720 did not modify the inactivation kinetics of KV3.1-encoded IK(DR), although it suppressed IK(DR) amplitude in these cells. Collectively, the perturbations by FTY720 on different types of K+ channels may contribute to the functional activities of immune cells, if similar findings appear in vivo.

Single K+ channels in adrenal zona glomerulosa cells. II. Inhibition by angiotensin II

1992 ◽  
Vol 263 (4) ◽  
pp. E760-E765 ◽  
Author(s):  
M. V. Kanazirska ◽  
P. M. Vassilev ◽  
S. J. Quinn ◽  
D. L. Tillotson ◽  
G. H. Williams
Keyword(s):  
Angiotensin Ii ◽  
Single Channel ◽  
Zona Glomerulosa ◽  
K Channel ◽  
Delayed Rectifier ◽  
Ang Ii ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Sequence Of Events ◽  
Voltage Dependent

The effects of angiotensin II (ANG II) on single K+ channels were studied in rat and bovine adrenal zona glomerulosa (ZG) cells, using the patch-clamp technique. ANG II (0.1-10 nM) induced substantial inhibition of inward rectifier and delayed rectifier K+ channel activities in rat and bovine ZG cells. Analysis of single-channel activities showed that the ANG II-induced channel-blocking effect involved reductions in the probability of the open state (Po) and the mean open time. The changes in these channel parameters occurred at all test voltages, indicating that the effect of ANG II was voltage independent. ANG II could not interact directly with the extracellular sides of the membranes in these experiments using cell-attached patches. Therefore, the effect of ANG II on K+ channels must occur through an indirect cytosolic transduction pathway. The ANG II-induced block of K+ channels will result in membrane depolarization, which may activate voltage-dependent Ca2+ channels, thereby increasing cytosolic free Ca2+ and stimulating aldosterone secretion. These channel-modulating actions of ANG II may be an important step in the initial sequence of events underlying its transduction mechanism.

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