K+ channels in adrenal zona glomerulosa cells. I. Characterization of distinct channel types

1992 ◽  
Vol 263 (4) ◽  
pp. E752-E759 ◽  
Author(s):  
P. M. Vassilev ◽  
M. V. Kanazirska ◽  
S. J. Quinn ◽  
D. L. Tillotson ◽  
G. H. Williams
Keyword(s):  
Single Channel ◽  
Zona Glomerulosa ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Delayed Rectifier ◽  
K Channels ◽  
Outward Currents ◽  
Positive Voltage ◽  
K Concentration ◽  
Inward Rectifier Channels

Four distinct types of K+ channels were identified in rat and bovine adrenal zona glomerulosa (ZG) cells and characterized using single-channel recording techniques. Inward rectifier channels were the most frequently observed K+ channel types in the membrane patches of both rat and bovine ZG cells. The slope conductance of the inward current was 42 pS with an extracellular K+ concentration of 150 mM. The probability of the open state of these channels increased with depolarization. With the use of inside-out membrane patches with symmetric 150 mM K+ solutions, the rectifying behavior was found to require Mg2+ on the intracellular side of the membrane. Delayed rectifier K+ channels with conductances of 27 and 48 pS were found with rat ZG cells. These channels persisted with prolonged positive voltage steps and showed long mean open times with increasing depolarization. Transient outward currents with a conductance of 28 pS were observed only in bovine ZG cells. These channels showed substantial inactivation during positive voltage steps of 250 ms duration. Ca(2+)-activated K+ channels with a large conductance (228 pS) were identified in rat and bovine ZG cells. These different classes of K+ channels may be important for the control of resting membrane potential and the generation of action potentials, thus participating in the regulation of Ca2+ influx and aldosterone secretion in ZG cells.

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.

Molecular physiology of cardiac potassium channels

1996 ◽  
Vol 76 (1) ◽  
pp. 49-67 ◽  
Author(s):  
K. K. Deal ◽  
S. K. England ◽  
M. M. Tamkun
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Single Channel ◽  
Resting Membrane Potential ◽  
Molecular Physiology ◽  
K Channels ◽  
Relative Contribution ◽  
Outward Currents ◽  
Important Challenge ◽  
Heterologous Expression Systems

The cardiac action potential results from the complex, but precisely regulated, movement of ions across the sarcolemmal membrane. Potassium channels represent the most diverse class of ion channels in heart and are the targets of several antiarrhythmic drugs. Potassium currents in the myocardium can be classified into one of two general categories: 1) inward rectifying currents such as IK1, IKACh, and IKATP; and 2) primarily voltage-gated currents such as IKs, IKr, IKp, IKur, and Ito. The inward rectifier currents regulate the resting membrane potential, whereas the voltage-activated currents control action potential duration. The presence of these multiple, often overlapping, outward currents in native cardiac myocytes has complicated the study of individual K+ channels; however, the application of molecular cloning technology to these cardiovascular K+ channels has identified the primary structure of these proteins, and heterologous expression systems have allowed a detailed analysis of the function and pharmacology of a single channel type. This review addresses the progress made toward understanding the complex molecular physiology of K+ channels in mammalian myocardium. An important challenge for the future is to determine the relative contribution of each of these cloned channels to cardiac function.

ANG II blocks potassium currents in zona glomerulosa cells from rat, bovine, and human adrenals

1991 ◽  
Vol 260 (5) ◽  
pp. E772-E779 ◽  
Author(s):  
U. Brauneis ◽  
P. M. Vassilev ◽  
S. J. Quinn ◽  
G. H. Williams ◽  
D. L. Tillotson
Keyword(s):  
Single Channel ◽  
Calcium Influx ◽  
Membrane Resistance ◽  
Zona Glomerulosa ◽  
Ang Ii ◽  
K Channels ◽  
Channel Interaction ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
K Currents

Angiotensin II (ANG II) is a principal secretagogue of adrenal zona glomerulosa (ZG) cells. The transduction process includes a depolarization of the plasma membrane and the activation of calcium influx. The ANG II-induced depolarization is associated with an increase in total membrane resistance. To directly address the mechanism underlying these observations, we examined the effect of ANG II on K+ currents of rat, bovine, and human ZG cells, using whole cell patch clamp. Although some differences were seen in the characteristics of K+ currents between species, ANG II consistently blocked outward currents in ZG cells [rat: 47.1 +/- 4.5% (SE), n = 17; bovine: 38.6 +/- 3.3%, n = 21; and human: 13-63%, n = 3]. With the use of the cell-attached mode, single-channel recordings in bovine ZG cells demonstrated K+ channels that were reversibly blocked when ANG II was added to the bath solution. This indicates that the block of K+ channels by ANG II involves a diffusible intracellular messenger rather than a direct receptor-channel interaction. The decreased conductance of K+ can account for the ANG II-induced membrane depolarization.

Single HERG delayed rectifier K+ channels expressed in Xenopus oocytes

1997 ◽  
Vol 272 (3) ◽  
pp. H1309-H1314 ◽  
Author(s):  
A. Zou ◽  
M. E. Curran ◽  
M. T. Keating ◽  
M. C. Sanguinetti
Keyword(s):  
Cardiac Myocytes ◽  
Xenopus Oocytes ◽  
Single Channel ◽  
K Channel ◽  
Delayed Rectifier ◽  
Class Iii ◽  
Channel Opening ◽  
The Mean ◽  
K Concentration ◽  
Channel Properties

HERG is a K+ channel with properties similar to the rapidly activating component (I(Kr)) of delayed rectifier K+ current, which is important for repolarization of human cardiac myocytes. In this study, we have characterized the single-channel properties of HERG expressed in Xenopus oocytes. Currents were measured in cell-attached patches with an extracellular K concentration of 120 mM. The single HERG channel conductance, determined at test potentials between -50 and -110 mV, was 12.1 +/- 0.6 pS. At positive test potentials (+40 to +80 mV), the probability of channel opening was low and slope conductance was 5.1 +/- 0.6 pS. The mean channel open times at -90 mV were 2.9 +/- 0.5 and 11.8 +/- 1.0 ms, and the mean channel closed times were 0.54 +/- 0.02 and 14.5 +/- 5.3 ms. Single HERG channels were blocked by MK-499, a class III antiarrhythmic agent that blocks I(Kr) in cardiac myocytes. The development of block was more rapid in inside-out patches than in cell-attached patches or in whole cell recordings, indicating that block occurs from the cytoplasmic side of the membrane. The single-channel properties of HERG are similar to I(Kr) channels of isolated cardiac myocytes, which provides further evidence that HERG proteins coassemble to form I(Kr) channels.

scholarly journals Nonindependent K+ Movement through the Pore in IRK1 Potassium Channels

1998 ◽  
Vol 112 (4) ◽  
pp. 475-484 ◽  
Author(s):  
Per Stampe ◽  
Jorge Arreola ◽  
Patricia Pérez-Cornejo ◽  
Ted Begenisich
Keyword(s):  
Single Channel ◽  
Flux Ratio ◽  
K Channel ◽  
Rate Theory ◽  
Voltage Range ◽  
K Channels ◽  
Shaker Channels ◽  
Absolute Reaction Rate ◽  
K Concentration ◽  
Permeation Models

We measured unidirectional K+ in- and efflux through an inward rectifier K channel (IRK1) expressed in Xenopus oocytes. The ratio of these unidirectional fluxes differed significantly from expectations based on independent ion movement. In an extracellular solution with a K+ concentration of 25 mM, the data were described by a Ussing flux-ratio exponent, n′, of ∼2.2 and was constant over a voltage range from −50 to −25 mV. This result indicates that the pore of IRK1 channels may be simultaneously occupied by at least three ions. The IRK1 n′ value of 2.2 is significantly smaller than the value of 3.5 obtained for Shaker K channels under identical conditions. To determine if other permeation properties that reflect multi-ion behavior differed between these two channel types, we measured the conductance (at 0 mV) of single IRK1 channels as a function of symmetrical K+ concentration. The conductance could be fit by a saturating hyperbola with a half-saturation K+ activity of 40 mM, substantially less than the reported value of 300 mM for Shaker K channels. We investigated the ability of simple permeation models based on absolute reaction rate theory to simulate IRK1 current–voltage, conductance, and flux-ratio data. Certain classes of four-barrier, three-site permeation models are inconsistent with the data, but models with high lateral barriers and a deep central well were able to account for the flux-ratio and single channel data. We conclude that while the pore in IRK1 and Shaker channels share important similarities, including K+ selectivity and multi-ion occupancy, they differ in other properties, including the sensitivity of pore conductance to K+ concentration, and may differ in the number of K+ ions that can simultaneously occupy the pore: IRK1 channels may contain three ions, but the pore in Shaker channels can accommodate four or more ions.

scholarly journals Membrane-delimited Inhibition of Maxi-K Channel Activity by the Intermediate Conductance Ca2+-activated K Channel

2006 ◽  
Vol 127 (2) ◽  
pp. 159-169 ◽  
Author(s):  
Jill Thompson ◽  
Ted Begenisich
Keyword(s):  
Single Channel ◽  
Expression System ◽  
Chemical Activation ◽  
K Channel ◽  
Channel Activity ◽  
Single Family ◽  
Open Probability ◽  
K Channels ◽  
Channel Proteins ◽  
K Activity

The complexity of mammalian physiology requires a diverse array of ion channel proteins. This diversity extends even to a single family of channels. For example, the family of Ca2+-activated K channels contains three structural subfamilies characterized by small, intermediate, and large single channel conductances. Many cells and tissues, including neurons, vascular smooth muscle, endothelial cells, macrophages, and salivary glands express more than a single class of these channels, raising questions about their specific physiological roles. We demonstrate here a novel interaction between two types of Ca2+-activated K channels: maxi-K channels, encoded by the KCa1.1 gene, and IK1 channels (KCa3.1). In both native parotid acinar cells and in a heterologous expression system, activation of IK1 channels inhibits maxi-K activity. This interaction was independent of the mode of activation of the IK1 channels: direct application of Ca2+, muscarinic receptor stimulation, or by direct chemical activation of the IK1 channels. The IK1-induced inhibition of maxi-K activity occurred in small, cell-free membrane patches and was due to a reduction in the maxi-K channel open probability and not to a change in the single channel current level. These data suggest that IK1 channels inhibit maxi-K channel activity via a direct, membrane-delimited interaction between the channel proteins. A quantitative analysis indicates that each maxi-K channel may be surrounded by four IK1 channels and will be inhibited if any one of these IK1 channels opens. This novel, regulated inhibition of maxi-K channels by activation of IK1 adds to the complexity of the properties of these Ca2+-activated K channels and likely contributes to the diversity of their functional roles.

ATP-sensitive K(+)-selective channels of inner medullary collecting duct cells

1994 ◽  
Vol 267 (3) ◽  
pp. F489-F496 ◽  
Author(s):  
S. C. Sansom ◽  
T. Mougouris ◽  
S. Ono ◽  
T. D. DuBose
Keyword(s):  
Single Channel ◽  
Collecting Duct ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Inner Medullary Collecting Duct ◽  
Outward Currents ◽  
Inward Currents ◽  
Excised Patches ◽  
Medullary Collecting Duct

The inner medullary collecting duct (IMCD) in vivo has the capacity to either secrete or reabsorb K+. However, a selective K+ conductance has not been described previously in the IMCD. In the present study, the patch-clamp method was used to determine the presence and properties of K(+)-selective channels in the apical membrane of the inner medullary collecting duct cell line, mIMCD-3. Two types of K(+)-selective channels were observed in both cell-attached and excised patches. The most predominant K+ channel, a smaller conductance K+ channel (SK), was present in cell-attached patches with 140 mM KCl (high bath K+) but not with 135 mM NaCl plus 5 mM KCl (low bath K+) in the bathing solution. The single-channel conductance of SK was 36 pS with inward currents and 29 pS with outward currents in symmetrical 140 mM KCl. SK was insensitive to both voltage and Ca2+. However, SK was inhibited significantly by millimolar concentrations of ATP in excised patches. A second K(+)-selective channel [a larger K+ channel (BK)] displayed a single-channel conductance equal to 132 pS with inward currents and 90 pS with outward currents in symmetrical 140 mM KCl solutions. BK was intermittently activated in excised inside-out patches by Mg(2+)-ATP in concentrations from 1 to 5 mM. With complete removal of Mg2+, BK was insensitive to ATP. BK was also insensitive to potential and Ca2+ and was observed in cell-attached patches with 140 mM KCl in the bath solution. Both channels were blocked reversibly by 1 mM Ba2+ from the intracellular surface but not by external Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Blocking Mechanisms of Ketamine and Its Enantiomers in Enzymatically Demyelinated Peripheral Nerve as Revealed by Single-channel Experiments

1997 ◽  
Vol 86 (2) ◽  
pp. 394-404 ◽  
Author(s):  
Michael E. Brau ◽  
Frank Sander ◽  
Werner Vogel ◽  
Gunter Hempelmann
Keyword(s):  
Potassium Channels ◽  
Peripheral Nerve ◽  
Ion Channel ◽  
Single Channel ◽  
Resting Potential ◽  
K Channel ◽  
Resting Membrane Potential ◽  
Na Channel ◽  
Ic50 Values ◽  
Sodium And Potassium

Background Ketamine shows, besides its general anesthetic effect, a local anesthetic-like action that is due to blocking of peripheral nerve sodium currents. In this study, the stereoselectivity of the blocking effects of the ketamine enantiomers S(+) and R(-) was investigated in sodium and potassium channels in peripheral nerve membranes. Methods Ion channel blockade of ketamine was investigated in enzymatically dissociated Xenopus sciatic nerves in multiple-channel and in single-channel outside-out patches. Results Concentration-effect curves for the Na+ peak current revealed half-maximal inhibiting concentrations (IC50) of 347 microM and 291 microM for S(+) and R(-) ketamine, respectively. The potential-dependent K+ current was less sensitive than the Na+ current with IC50 values of 982 microM and 942 microM. The most sensitive ion channel was the flickering background K+ channel, with IC50 values of 168 microM and 146 microM for S(+) and R(-) ketamine. Competition experiments suggest one binding site at the flicker K+ channel, with specific binding affinities for each of the enantiomers. For the Na+ channel, the block was weaker in acidic (pH = 6.6) than in neutral (pH = 7.4) and basic (pH = 8.2) solutions; for the flicker K+ channel, the block was weaker in acidic and stronger in basic solutions. Conclusions Ketamine blockade of sodium and potassium channels in peripheral nerve membranes shows no stereoselectivity except for the flicker K+ channel, which showed a very weak stereoselectivity in favor of the R(-) form. This potential-insensitive flicker K+ channel may contribute to the resting potential. Block of this channel and subsequent depolarization of the resting membrane potential leads, besides to direct Na+ channel block, to inexcitability via Na+ channel inactivation.

Basolateral potassium channels in renal proximal tubule

1987 ◽  
Vol 253 (3) ◽  
pp. F476-F487 ◽  
Author(s):  
H. Sackin ◽  
L. G. Palmer
Keyword(s):  
Single Channel ◽  
Basolateral Membrane ◽  
K Channel ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
K Channels ◽  
Open Time ◽  
Excised Patches ◽  
The Mean ◽  
Inside Out

Potassium (K+) channels in the basolateral membrane of unperfused Necturus proximal tubules were studied in both cell-attached and excised patches, after removal of the tubule basement membrane by manual dissection without collagenase. Two different K+ channels were identified on the basis of their kinetics: a short open-time K+ channel, with a mean open time less than 1 ms, and a long open-time K+ channel with a mean open time greater than 20 ms. The short open-time channel occurred more frequently than the longer channel, especially in excised patches. For inside-out excised patches with Cl- replaced by gluconate, the current-voltage relation of the short open-time K+ channel was linear over +/- 60 mV, with a K+-Na+ selectivity of 12 +/- 2 (n = 12), as calculated from the reversal potential with oppositely directed Na+ and K+ gradients. With K-Ringer in the patch pipette and Na-Ringer in the bath, the conductance of the short open-time channel was 47 +/- 2 pS (n = 15) for cell-attached patches, 26 +/- 2 pS (n = 15) for patches excised (inside out) into Na-Ringer, and 36 +/- 6 pS (n = 3) for excised patches with K-Ringer on both sides. These different conductances can be partially explained by a dependence of single-channel conductance on the K+ concentration on the interior side of the membrane. In experiments with a constant K+ gradient across excised patches, large changes in Na+ at the interior side of the membrane produced no change in single-channel conductance, arguing against a direct block of the K+ channel by Na+. Finally, the activity of the short open-time channel was voltage gated, where the mean number of open channels decreased as a linear function of basolateral membrane depolarization for potentials between -60 and 0 mV. Depolarization from -60 to -40 mV decreased the mean number of open K+ channels by 28 +/- 8% (n = 6).

scholarly journals Effect of Auxin (IAA) on the Fast Vacuolar (FV) Channels in Red Beet (Beta vulgaris L.) Taproot Vacuoles

2020 ◽  
Vol 21 (14) ◽  
pp. 4876
Author(s):  
Zbigniew Burdach ◽  
Agnieszka Siemieniuk ◽  
Waldemar Karcz
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
K Channel ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Inward Current ◽  
Bath Solution ◽  
Outward Currents ◽  
Inward Currents

In contrast to the well-studied effect of auxin on the plasma membrane K+ channel activity, little is known about the role of this hormone in regulating the vacuolar K+ channels. Here, the patch-clamp technique was used to investigate the effect of auxin (IAA) on the fast-activating vacuolar (FV) channels. It was found that the macroscopic currents displayed instantaneous currents, which at the positive potentials were about three-fold greater compared to the one at the negative potentials. When auxin was added to the bath solution at a final concentration of 1 µM, it increased the outward currents by about 60%, but did not change the inward currents. The imposition of a ten-fold vacuole-to-cytosol KCl gradient stimulated the efflux of K+ from the vacuole into the cytosol and reduced the K+ current in the opposite direction. The addition of IAA to the bath solution with the 10/100 KCl gradient decreased the outward current and increased the inward current. Luminal auxin reduced both the outward and inward current by approximately 25% compared to the control. The single channel recordings demonstrated that cytosolic auxin changed the open probability of the FV channels at the positive voltages to a moderate extent, while it significantly increased the amplitudes of the single channel outward currents and the number of open channels. At the positive voltages, auxin did not change the unitary conductance of the single channels. We suggest that auxin regulates the activity of the fast-activating vacuolar (FV) channels, thereby causing changes of the K+ fluxes across the vacuolar membrane. This mechanism might serve to tightly adjust the volume of the vacuole during plant cell expansion.

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