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 State-dependent Block of BK Channels by Synthesized Shaker Ball Peptides

2006 ◽  
Vol 128 (4) ◽  
pp. 423-441 ◽  
Author(s):  
Weiyan Li ◽  
Richard W. Aldrich
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Kinetic Measurements ◽  
K Channels ◽  
Functional Studies ◽  
State Dependent ◽  
Quaternary Ammonium Ions ◽  
Pore Lining ◽  
Cytoplasmic Side

Crystal structures of potassium channels have strongly corroborated an earlier hypothetical picture based on functional studies, in which the channel gate was located on the cytoplasmic side of the pore. However, accessibility studies on several types of ligand-sensitive K+ channels have suggested that their activation gates may be located near or within the selectivity filter instead. It remains to be determined to what extent the physical location of the gate is conserved across the large K+ channel family. Direct evidence about the location of the gate in large conductance calcium-activated K+ (BK) channels, which are gated by both voltage and ligand (calcium), has been scarce. Our earlier kinetic measurements of the block of BK channels by internal quaternary ammonium ions have raised the possibility that they may lack a cytoplasmic gate. We show in this study that a synthesized Shaker ball peptide (ShBP) homologue acts as a state-dependent blocker for BK channels when applied internally, suggesting a widening at the intracellular end of the channel pore upon gating. This is consistent with a gating-related conformational change at the cytoplasmic end of the pore-lining helices, as suggested by previous functional and structural studies on other K+ channels. Furthermore, our results from two BK channel mutations demonstrate that similar types of interactions between ball peptides and channels are shared by BK and other K+ channel types.

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.

Inhibition of slow-wave repolarization and Ca(2+)-activated K+ channels by quaternary ammonium ions

1993 ◽  
Vol 264 (3) ◽  
pp. C625-C631 ◽  
Author(s):  
A. Carl ◽  
B. W. Frey ◽  
S. M. Ward ◽  
K. M. Sanders ◽  
J. L. Kenyon
Keyword(s):  
Smooth Muscle ◽  
Binding Site ◽  
Slow Wave ◽  
Voltage Dependence ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Patch Clamp Technique ◽  
K Channels ◽  
Circular Smooth Muscle

We studied the effects of the K+ channel blocker tetrapentylammonium (TPeA) on the electrical activity of intact circular smooth muscle from canine colon. TPeA (10 and 20 microM) increased slow-wave duration and "locked" the membrane potential around -30 mV plateau potential after several minutes of application, suggesting that K+ channels are essential for termination of colonic slow waves. Repolarization and normal slow-wave activity resumed after 20-30 min of washout. The patch-clamp technique was used to study the block of large-conductance Ca(2+)-activated K+ channels (BK channels) by TPeA and tetraethylammonium (TEA) in excised and cell-attached patches from isolated colonic smooth muscle cells. Channel block was characterized by a voltage-dependent dissociation constant [Kd(V)] for the binding of TEA and TPeA to a blocking site located a fraction of the distance across the membrane field (delta). The extracellular TEA binding site had a Kd(0) of 0.33 mM and a delta of 0.23. The extracellular TPeA binding site had a Kd(0) of 2.2 mM but showed significantly less voltage dependence (delta = 0.02). The intracellular binding site for TEA was of low affinity [Kd(0) = 76 mM]. Intracellular TPeA was the most potent blocker of BK channel current [Kd(0) = 11.7 microM]. The voltage dependence of block by intracellular TPeA (delta = -0.21) was not significantly different from that of intracellular TEA (delta = -0.3). Internal TPeA (10 microM) also blocked a 70-pS K+ channel and a 23-pS K+ channel.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Evidence for KCNQ1 K+ channel expression in rat zymogen granule membranes and involvement in cholecystokinin-induced pancreatic acinar secretion

2008 ◽  
Vol 294 (4) ◽  
pp. C879-C892 ◽  
Author(s):  
Wing-Kee Lee ◽  
Blazej Torchalski ◽  
Eleni Roussa ◽  
Frank Thévenod
Keyword(s):  
Single Channel ◽  
Reversal Potential ◽  
Fluid Secretion ◽  
Pancreatic Tissue ◽  
Bk Channel ◽  
K Channel ◽  
Amylase Secretion ◽  
Zymogen Granule ◽  
Open Probability ◽  
Pancreatic Acini

Secretion of enzymes and fluid induced by Ca2+ in pancreatic acini is not completely understood and may involve activation of ion conductive pathways in zymogen granule (ZG) membranes. We hypothesized that a chromanol 293B-sensitive K+ conductance carried by a KCNQ1 protein is expressed in ZG membranes (ZGM). In suspensions of rat pancreatic ZG, ion flux was determined by ionophore-induced osmotic lysis of ZG suspended in isotonic salts. The KCNQ1 blocker 293B selectively blocked K+ permeability (IC50 of ∼10 μM). After incorporation of ZGM into planar bilayer membranes, cation channels were detected in 645/150 mM potassium gluconate cis/trans solutions. Channels had linear current-voltage relationships, a reversal potential ( Erev) of −20.9 ± 0.9 mV, and a single-channel K+ conductance ( gK) of 265.8 ± 44.0 pS ( n = 39). Replacement of cis 500 mM K+ by 500 mM Na+ shifted Erev to −2.4 ± 3.6 mV ( n = 3), indicating K+ selectivity. Single-channel analysis identified several K+ channel groups with distinct channel behaviors. K+ channels with a gK of 651.8 ± 88.0 pS, Erev of −22.9 ± 2.2 mV, and open probability ( Popen) of 0.43 ± 0.06 at 0 mV ( n = 6) and channels with a gK of 155.0 ± 11.4 pS, Erev of −18.3 ± 1.8 mV, and Popen of 0.80 ± 0.03 at 0 mV ( n = 3) were inhibited by 100 μM 293B or by the more selective inhibitor HMR-1556 but not by the maxi-Ca2+-activated K+ channel (BK channel) inhibitor charybdotoxin (5 nM). KCNQ1 protein was demonstrated by immunoperoxidase labeling of pancreatic tissue, immunogold labeling of ZG, and immunoblotting of ZGM. 293B also inhibited cholecystokinin-induced amylase secretion of permeabilized acini (IC50 of ∼10 μM). Thus KCNQ1 may account for ZG K+ conductance and contribute to pancreatic hormone-stimulated enzyme and fluid secretion.

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.

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)

scholarly journals Selectivity filter gating in large-conductance Ca2+-activated K+ channels

2012 ◽  
Vol 139 (3) ◽  
pp. 235-244 ◽  
Author(s):  
Jill Thompson ◽  
Ted Begenisich
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
Selectivity Filter ◽  
Channel Blockers ◽  
Intracellular Location ◽  
K Channels ◽  
Kv Channels ◽  
Quaternary Ammonium Ions ◽  
Tetrabutyl Ammonium ◽  
Opposite Behavior

Membrane voltage controls the passage of ions through voltage-gated K (Kv) channels, and many studies have demonstrated that this is accomplished by a physical gate located at the cytoplasmic end of the pore. Critical to this determination were the findings that quaternary ammonium ions and certain peptides have access to their internal pore-blocking sites only when the channel gates are open, and that large blocking ions interfere with channel closing. Although an intracellular location for the physical gate of Kv channels is well established, it is not clear if such a cytoplasmic gate exists in all K+ channels. Some studies on large-conductance, voltage- and Ca2+-activated K+ (BK) channels suggest a cytoplasmic location for the gate, but other findings question this conclusion and, instead, support the concept that BK channels are gated by the pore selectivity filter. If the BK channel is gated by the selectivity filter, the interactions between the blocking ions and channel gating should be influenced by the permeant ion. Thus, we tested tetrabutyl ammonium (TBA) and the Shaker “ball” peptide (BP) on BK channels with either K+ or Rb+ as the permeant ion. When tested in K+ solutions, both TBA and the BP acted as open-channel blockers of BK channels, and the BP interfered with channel closing. In contrast, when Rb+ replaced K+ as the permeant ion, TBA and the BP blocked both closed and open BK channels, and the BP no longer interfered with channel closing. We also tested the cytoplasmically gated Shaker K channels and found the opposite behavior: the interactions of TBA and the BP with these Kv channels were independent of the permeant ion. Our results add significantly to the evidence against a cytoplasmic gate in BK channels and represent a positive test for selectivity filter gating.

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