scholarly journals External monovalent cations that impede the closing of K channels.

1986 ◽  
Vol 87 (5) ◽  
pp. 795-816 ◽  
Author(s):  
D R Matteson ◽  
R P Swenson
Keyword(s):  
Channel Gating ◽  
Reversal Potential ◽  
Monovalent Cation ◽  
K Channel ◽  
Monovalent Cations ◽  
Large Shift ◽  
K Channels ◽  
Voltage Curve ◽  
Voltage Relationship ◽  
Closing Rate

We have examined the effects of a variety of monovalent cations on K channel gating in squid giant axons. The addition of the permeant cations K, Rb, or Cs to the external medium decreases the channel closing rate and causes a negative shift of the conductance-voltage relationship. Both of these effects are larger in Rb than in K. The opening kinetics of the K channel are, on the other hand, unaffected by these monovalent cations. Other permeant species, like NH4 and Tl, slightly increase the closing rate, whereas the relatively impermeant cations Na, Li, and Tris have little or no effect on K channel gating. The permeant cations have different effects on the reversal potential and the shape of the instantaneous current-voltage relationship. These effects give information about entry and binding of the cations in K channels. Rb, for example, enters the pore readily (large shift of the reversal potential), but binds tightly to the channel interior, inhibiting current flow. We find a correlation between the occupancy of the channel by a monovalent cation and the closing rate, and conclude that the presence of a monovalent cation in the pore inhibits channel closing, and thereby causes a leftward shift in the activation-voltage curve. In causing these effects, the cations appear to bind near the inner surface of the membrane.

scholarly journals The role of calcium ions in the closing of K channels.

1986 ◽  
Vol 87 (5) ◽  
pp. 817-832 ◽  
Author(s):  
C M Armstrong ◽  
D R Matteson
Keyword(s):  
Time Course ◽  
External Surface ◽  
Monovalent Cation ◽  
K Channel ◽  
Monovalent Cations ◽  
K Channels ◽  
Channel Opening ◽  
Voltage Curve ◽  
Channel Properties

The effects of external Ca ion on K channel properties were studied in squid giant axons. Increasing the Ca concentration from 20 to 100 mM slowed K channel opening, and was kinetically equivalent to decreasing the depolarizing step by approximately 25 mV. The same Ca increase had a much smaller effect on closing kinetics, equivalent to making the membrane potential more negative by approximately mV. With regard to the conductance-voltage curve, this Ca increase was about equivalent to decreasing the depolarizing step by approximately 10 mV. The presence of K or Rb in the bath slowed closing kinetics and made the time course more complex: there were pronounced slow components in Rb and, to a lesser extent, in K. Increasing the Ca concentration strongly antagonized the slowing caused by Rb or K. Thus, Ca has a strong effect on closing kinetics only in the presence of these monovalent cations. Rb and K do not significantly alter opening kinetics, nor do they alter Ca's ability to slow opening kinetics. High Ca slightly affects the instantaneous I-V curve by selectively depressing inward current at negative voltages. The results imply that Ca has two actions on K channels, and in only one, the action on closing, does it compete with monovalent cations. We propose (a) that opening kinetics are slowed by binding of Ca to negatively charged parts of the gating apparatus that are at the external surface of the channel protein when the channel is closed; monovalent cations do not compete effectively in this action; (b) Ca (or possibly Mg) normally occupies closed channels and has a latching effect. External K or Rb competes with Ca for channel occupancy. Channels close sluggishly when occupied by a monovalent cation and tend to reopen. Thus, slow closing results from occupancy by K or Rb instead of Ca. The data are well fit by a model based on these ideas.

scholarly journals Interaction of internal anions with potassium channels of the squid giant axon.

1983 ◽  
Vol 82 (4) ◽  
pp. 429-448 ◽  
Author(s):  
D J Adams ◽  
G S Oxford
Keyword(s):  
Prolonged Exposure ◽  
Channel Gating ◽  
Reversal Potential ◽  
Inorganic Anions ◽  
K Channel ◽  
Delayed Rectifier ◽  
K Channels ◽  
Gating Mechanism ◽  
Inorganic Species ◽  
K Currents

The interaction of internal anions with the delayed rectifier potassium channel was studied in perfused squid axons. Changing the internal potassium salt from K+ glutamate- to KF produced a reversible decline of outward K currents and a marked slowing of the activation of K channels at all voltages. Fluoride ions exert a differential effect upon K channel gating kinetics whereby activation of IK during depolarizing steps is slowed dramatically, but the rate of closing after the step is not much altered. These effects develop with a slow time course (30-60 min) and are specific for K channels over Na channels. Both the amplitude and activation rate of IK were restored within seconds upon return to internal glutamate solutions. The fluoride effect is independent of the external K+ concentration and test membrane potential, and does not recover with repetitive application of depolarizing voltage steps. Of 11 different anions tested, all inorganic species induced similar decreases and slowing of IK, while K currents were maintained during extended perfusion with several organic anions. Anions do not alter the reversal potential or shape of the instantaneous current-voltage relation of open K channels. The effect of prolonged exposure to internal fluoride could be partially reversed by the addition of cationic K channel blocking agents such as TEA+, 4-AP+, and Cs+. The competitive antagonism between inorganic anions and internal cationic K channel blockers suggests that they may interact at a related site(s). These results indicate that inorganic anions modify part of the K channel gating mechanism (activation) at a locus near the inner channel surface.

scholarly journals Effector Contributions to Gβγ-mediated Signaling as Revealed by Muscarinic Potassium Channel Gating

1997 ◽  
Vol 109 (2) ◽  
pp. 245-253 ◽  
Author(s):  
Tatyana T. Ivanova-Nikolova ◽  
Gerda E. Breitwieser
Keyword(s):  
G Proteins ◽  
Channel Gating ◽  
K Channel ◽  
Heterotrimeric G Proteins ◽  
K Channels ◽  
Protein Activation ◽  
G Protein Activation ◽  
Extracellular Stimuli ◽  
Acetylcholine Concentration ◽  
Signaling Process

Receptor-mediated activation of heterotrimeric G proteins leading to dissociation of the Gα subunit from Gβγ is a highly conserved signaling strategy used by numerous extracellular stimuli. Although Gβγ subunits regulate a variety of effectors, including kinases, cyclases, phospholipases, and ion channels (Clapham, D.E., and E.J. Neer. 1993. Nature (Lond.). 365:403–406), few tools exist for probing instantaneous Gβγ-effector interactions, and little is known about the kinetic contributions of effectors to the signaling process. In this study, we used the atrial muscarinic K+ channel, which is activated by direct interactions with Gβγ subunits (Logothetis, D.E., Y. Kurachi, J. Galper, E.J. Neer, and D.E. Clap. 1987. Nature (Lond.). 325:321–326; Wickman, K., J.A. Iniguez-Liuhi, P.A. Davenport, R. Taussig, G.B. Krapivinsky, M.E. Linder, A.G. Gilman, and D.E. Clapham. 1994. Nature (Lond.). 366: 654–663; Huang, C.-L., P.A. Slesinger, P.J. Casey, Y.N. Jan, and L.Y. Jan. 1995. Neuron. 15:1133–1143), as a sensitive reporter of the dynamics of Gβγ-effector interactions. Muscarinic K+ channels exhibit bursting behavior upon G protein activation, shifting between three distinct functional modes, characterized by the frequency of channel openings during individual bursts. Acetylcholine concentration (and by inference, the concentration of activated Gβγ) controls the fraction of time spent in each mode without changing either the burst duration or channel gating within individual modes. The picture which emerges is of a Gβγ effector with allosteric regulation and an intrinsic “off” switch which serves to limit its own activation. These two features combine to establish exquisite channel sensitivity to changes in Gβγ concentration, and may be indicative of the factors regulating other Gβγ-modulated effectors.

Effect of H+ on ATP-regulated K+ channels in feline ventricular myocytes

1991 ◽  
Vol 261 (3) ◽  
pp. H755-H761 ◽  
Author(s):  
J. Cuevas ◽  
A. L. Bassett ◽  
J. S. Cameron ◽  
T. Furukawa ◽  
R. J. Myerburg ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Reversal Potential ◽  
State Probability ◽  
K Channel ◽  
K Channels ◽  
Open Time ◽  
Current Voltage ◽  
Effects Of Ph ◽  
The Mean ◽  
Current Voltage Relationship

Using patch-clamp techniques, we examined the effects of pH on properties of ATP-regulated K+ channels in single myocytes isolated from cat left ventricles. ATP-K+ channels of inside-out patches were bilaterally exposed to 140 mM K+ solutions (22 degrees C). In the absence of ATP and Mg2+, the channels had a linear current-voltage relationship during hyperpolarizing pulses (20-100 mV negative to the reversal potential) at both intracellular pH (pHi) 7.4 and 6.5, but the slope conductance was 66 +/- 2 pS at pHi 7.4 and 46 +/- 2 pS at pHi 6.5. Lowering pHi from 7.4 to 6.5 increased the mean open time (from 15.9 +/- 4.6 to 35.9 +/- 7.9 ms, P less than 0.01) but decreased the open-state probability measured at 50 mV positive to the reversal potential (from 0.35 +/- 0.04 to 0.16 +/- 0.04, P less than 0.01). However, in the presence of both 0.2 mM ATP and 1 mM MgCl2, lowering pHi from 7.4 to 6.5 increased the mean open time (from 5.0 +/- 2.6 to 17.9 +/- 5.9 ms, P less than 0.01) and the open-state probability (from 0.025 +/- 0.010 to 0.098 +/- 0.024, P less than 0.01). These data indicate that increases in intracellular H+ concentration modulate cardiac ATP-K+ channel properties. Ischemia-associated decreases in pHi may enhance the opening of cardiac ATP-regulated K+ channels and resultant action potential shortening.

Apical K+ conductance in maturing rabbit principal cell

1997 ◽  
Vol 272 (3) ◽  
pp. F397-F404 ◽  
Author(s):  
L. M. Satlin ◽  
L. G. Palmer
Keyword(s):  
Reversal Potential ◽  
Principal Cell ◽  
K Channel ◽  
Postnatal Life ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
K Channels ◽  
Inward Currents ◽  
K Secretion

Net K+ secretion is not detected in cortical collecting ducts (CCDs) isolated from newborn rabbits and perfused in vitro. To establish whether a low apical K+ permeability of the neonatal principal cell limits K+ secretion early in life, we used the patch-clamp technique in split-open CCDs isolated from maturing rabbits to study the properties and density of conducting K+ channels in principal cells. With KCl in the pipette and a NaCl solution warmed to 37 degrees C in the bath, inward currents with a conductance of approximately 42 pS were observed in 0% (0 out of 13 or 0/13), 10% (2/21), 18% (5/28), 29% (4/14), and 56% (10/18) of cell-attached patches obtained in 1-, 2-, 3-, 4-, and 5-wk-old animals, respectively. The conductance and reversal potential of this channel led us to suspect that it represented the low-conductance K+ channel previously described in the rat CCD by L. G. Palmer, L. Antonian, and G. Frindt (J. Gen. Physiol. 104: 693-710, 1994). The mean number of open channels per patch (NPo) increased progressively (P < 0.05) after birth, from 0 at 1 wk, to 0.06 +/- 0.04 at 2 wk, to 0.40 +/- 0.18 at 3 wk, to 0.74 +/- 0.41 at 4 wk, and to 1.06 +/- 0.28 at 5 wk. The increase in NPo appeared to be due primarily to a developmental increase in N, which is the number of channels; open probability, Po, remained constant at approximately 0.5 for all channels identified after the 2nd wk of life. The increase in number of conducting K+ channels during postnatal life is likely to contribute to the maturational increase in net K+ secretion in the CCDs.

Modulation of rabbit aortic Ca(2+)-activated K+ channels by pinacidil, cromakalim, and glibenclamide

1993 ◽  
Vol 264 (5) ◽  
pp. C1119-C1127 ◽  
Author(s):  
G. H. Gelband ◽  
J. R. McCullough
Keyword(s):  
Lipid Bilayers ◽  
Bk Channels ◽  
Voltage Sensitivity ◽  
Monovalent Cations ◽  
K Channels ◽  
Channel Modulation ◽  
Aortic Smooth Muscle ◽  
Maximum Value ◽  
Open Time ◽  
Voltage Relationship

Rabbit aortic smooth muscle microsomes were isolated and large-conductance Ca(2+)-activated K+ (BK) channels incorporated into planar lipid bilayers. The selectivity sequence and relative permeability ratios for monovalent cations was K+ (1.0) > Rb+ (0.68) > NH4+ (0.14) >> Na+, Cs+ (< 0.05). Application of pinacidil or cromakalim (0.05-10 microM) shifted the probability of opening (Po)-voltage relationship in the hyperpolarizing direction. The concentrations of pinacidil and cromakalim required to increase Po 50% of the maximum value at -40 mV were 0.96 +/- 0.04 and 0.52 +/- 0.03 microM, respectively. Neither pinacidil nor cromakalim altered the voltage sensitivity of the channel (11-13 mV/e-fold change in Po). Kinetic analysis of data at -40 mV demonstrated that pinacidil (1 microM) decreased the length of time the channel dwelled in its long-closed state by 50% from 173 +/- 50 to 86 +/- 19 ms. No significant change was observed for the open time constant (20 ms). Glibenclamide (10 microM) had no effect on Po of BK channels. However, glibenclamide reversed the pinacidil- or cromakalim-stimulated increase in Po of BK channels. These data suggest that both cromakalim and pinacidil increased the probability of opening of single rabbit aortic large-conductance Ca(2+)-activated K+ channels and that this channel modulation may contribute to the vasorelaxant properties of these drugs.

scholarly journals Redox Regulation of Large Conductance Ca2+-activated K+ Channels in Smooth Muscle Cells

1997 ◽  
Vol 110 (1) ◽  
pp. 35-44 ◽  
Author(s):  
Zhao-Wen Wang ◽  
Masayuki Nara ◽  
Yong-Xiao Wang ◽  
Michael I. Kotlikoff
Keyword(s):  
Redox Regulation ◽  
Channel Gating ◽  
K Channel ◽  
Dependent Manner ◽  
Channel Activity ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
Sulfhydryl Oxidation ◽  
Excised Patches ◽  
Redox Agents

The effects of sulfhydryl reduction/oxidation on the gating of large-conductance, Ca2+-activated K+ (maxi-K) channels were examined in excised patches from tracheal myocytes. Channel activity was modified by sulfhydryl redox agents applied to the cytosolic surface, but not the extracellular surface, of membrane patches. Sulfhydryl reducing agents dithiothreitol, β-mercaptoethanol, and GSH augmented, whereas sulfhydryl oxidizing agents diamide, thimerosal, and 2,2′-dithiodipyridine inhibited, channel activity in a concentration-dependent manner. Channel stimulation by reduction and inhibition by oxidation persisted following washout of the compounds, but the effects of reduction were reversed by subsequent oxidation, and vice versa. The thiol-specific reagents N-ethylmaleimide and (2-aminoethyl)methanethiosulfonate inhibited channel activity and prevented the effect of subsequent sulfhydryl oxidation. Measurements of macroscopic currents in inside-out patches indicate that reduction only shifted the voltage/nPo relationship without an effect on the maximum conductance of the patch, suggesting that the increase in nPo following reduction did not result from recruitment of more functional channels but rather from changes of channel gating. We conclude that redox modulation of cysteine thiol groups, which probably involves thiol/disulfide exchange, alters maxi-K channel gating, and that this modulation likely affects channel activity under physiological conditions.

scholarly journals Pharmacological and kinetic analysis of K channel gating currents.

1989 ◽  
Vol 93 (2) ◽  
pp. 263-283 ◽  
Author(s):  
S Spires ◽  
T Begenisich
Keyword(s):  
Channel Gating ◽  
K Channel ◽  
Na Channel ◽  
Gating Current ◽  
Channel Conductance ◽  
Gating Currents ◽  
Current Time ◽  
Time Constants ◽  
K Channels ◽  
Low Concentrations

We have measured gating currents from the squid giant axon using solutions that preserve functional K channels and with experimental conditions that minimize Na channel contributions to these currents. Two pharmacological agents were used to identify a component of gating current that is associated with K channels. Low concentrations of internal Zn2+ that considerably slow K channel ionic currents with no effect on Na channel currents altered the component of gating current associated with K channels. At low concentrations (10-50 microM) the small, organic, dipolar molecule phloretin has several reported specific effects on K channels: it reduces K channel conductance, shifts the relationship between channel conductance and membrane voltage (Vm) to more positive potentials, and reduces the voltage dependence of the conductance-Vm relation. The K channel gating charge movements were altered in an analogous manner by 10 microM phloretin. We also measured the dominant time constants of the K channel ionic and gating currents. These time constants were similar over part of the accessible voltage range, but at potentials between -40 and 0 mV the gating current time constants were two to three times faster than the corresponding ionic current values. These features of K channel function can be reproduced by a simple kinetic model in which the channel is considered to consist of two, two-state, nonidentical subunits.

Novel actions of ryanodine and analogues—Perturbers of potassium channels

1995 ◽  
Vol 15 (6) ◽  
pp. 515-530 ◽  
Author(s):  
H. Vais ◽  
P. N. R. Usherwood
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Bk Channel ◽  
Muscle Membrane ◽  
K Channel ◽  
Similar Data ◽  
Ionic Selectivity ◽  
K Channels ◽  
Quaternary Ammonium Ions ◽  
Ik Channel

The effects of ryanodine, 9,21-didehydroryanodine and 9,21-didehydroryanodol on two types of K+ channel (a maxi, Ca2+-activated, 170 pS channel (BK channel) and an inward rectifier, stretch-sensitive channel of 35 pS conductance (IK channel) found in the plasma membrane of locust skeletal muscle have been investigated. 10−9M-10−5M ryanodine irreversibly induced a dose-dependent reduction of the reversal potential (Vrev) of the currents of both channels, i.e. from ~60 mV in the absence of the alkaloid to ~15 mV for 10−5M ryanodine, measured under physiologically normal K+ and Na+ gradients. In both cases the change in the ionic selectivity was Ca2+-independent. 9,21-didehydroryanodine and 9,21-didehyroryanodol also reduced Vrev, but only to ~35 mV during application of 10−5M of these compounds. Additionally, 9,21-didehydroryanodine reversibly diminished the conductances of the two K+ channels. To test the hypothesis that ryanoids increase Na+ permeability by enlarging the K+ channels, the channels were probed with quaternary ammonium ions during ryanoid application. When applied to the cytoplasmic face of inside-out patches exised from locust muscle membrane, TEA blocked the K+ channels in a voltage-dependent fashion. The dissociation constant (Kd(0)) for TEA block of the IK channel was reduced from 44 mM to 1 mM by 10−7 M ryanodine, but the voltage-dependence of the block was unaffected. Qualitatively similar data were obtained for the BK channel. Ryanodine had no effect on the Kd for cytoplasmically-applied TMA. However, the voltage-dependence for TMA block was increased for both K+ channels, from 0.47 to ~0.8 with 10−6M ryanodine. The effects of ryanodine on TEA and TMA block support the hypothesis that ryanodine enlarges the K+ channels so as to facilitate permeation of partially hydrated Na+ ions.

scholarly journals Selectivity and gating of the type L potassium channel in mouse lymphocytes.

1991 ◽  
Vol 97 (6) ◽  
pp. 1227-1250 ◽  
Author(s):  
M S Shapiro ◽  
T E DeCoursey
Keyword(s):  
Relative Permeability ◽  
Single Channel ◽  
Reversal Potential ◽  
K Channel ◽  
Ionic Selectivity ◽  
Myelinated Nerve ◽  
Small Component ◽  
Whole Cell ◽  
K Channels ◽  
Single Channel Currents

Type l voltage-gated K+ channels in murine lymphocytes were studied under voltage clamp in cell-attached patches and in the whole-cell configuration. The kinetics of activation of whole-cell currents during depolarizing pulses could be fit by a single exponential after an initial delay. Deactivation upon repolarization of both macroscopic and microscopic currents was mono-exponential, except in Rb-Ringer or Cs-Ringer solution in which tail currents often displayed "hooks," wherein the current first increased or remained constant before decaying. In some cells type l currents were contaminated by a small component due to type n K+ channels, which deactivate approximately 10 times slower than type l channels. Both macroscopic and single channel currents could be dissected either kinetically or pharmacologically into these two K+ channel types. The ionic selectivity and conductance of type l channels were studied by varying the internal and external permeant ion. With 160 mM K+ in the cell, the relative permeability calculated from the reversal potential with the Goldman-Hodgkin-Katz equation was K+ (identical to 1.0) greater than Rb+ (0.76) greater than NH4+ = Cs+ (0.12) much greater than Na+ (less than 0.004). Measured 30 mV negative to the reversal potential, the relative conductance sequence was quite different: NH4+ (1.5) greater than K+ (identical to 1.0) greater than Rb+ (0.5) greater than Cs+ (0.06) much greater than Na+, Li+, TMA+ (unmeasurable). Single channel current rectification resembled that of the whole-cell instantaneous I-V relation. Anomalous mole-fraction dependence of the relative permeability PNH4/PK was observed in NH4(+)-K+ mixtures, indicating that the type l K+ channel is a multi-ion pore. Compared with other K+ channels, lymphocyte type l K+ channels are most similar to "g12" channels in myelinated nerve.

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