scholarly journals Dihydropyridine Action on Voltage-dependent Potassium Channels Expressed in Xenopus Oocytes

1997 ◽  
Vol 109 (2) ◽  
pp. 169-180 ◽  
Author(s):  
Vladimir Avdonin ◽  
Erwin F. Shibata ◽  
Toshinori Hoshi
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Xenopus Oocytes ◽  
K Channels ◽  
Open Time ◽  
Voltage Dependent ◽  
Ca2 Channels

Dihydropyridines (DHPs) are well known for their effects on L-type voltage-dependent Ca2+ channels. However, these drugs also affect other voltage-dependent ion channels, including Shaker K+ channels. We examined the effects of DHPs on the Shaker K+ channels expressed in Xenopus oocytes. Intracellular applications of DHPs quickly and reversibly induced apparent inactivation in the Shaker K+ mutant channels with disrupted N- and C-type inactivation. We found that DHPs interact with the open state of the channel as evidenced by the decreased mean open time. The DHPs effects are voltage-dependent, becoming more effective with hyperpolarization. A model which involves binding of two DHP molecules to the channel is consistent with the results obtained in our experiments.

Uterine Excitability and Ion Channels and Their Changes with Gestation and Hormonal Environment

2020 ◽  
Vol 83 (1) ◽  
Author(s):  
Susan Wray ◽  
Sarah Arrowsmith
Keyword(s):  
Ion Channels ◽  
Inward Rectifier ◽  
Cation Channels ◽  
Annual Review ◽  
Publication Date ◽  
K Channels ◽  
Voltage Gated ◽  
New Findings ◽  
Voltage Dependent ◽  
Pore Domain

We address advances in the understanding of myometrial physiology, focusing on excitation and the effects of gestation on ion channels and their relevance to labor. This review moves through pioneering studies to exciting new findings. We begin with the myometrium and its myocytes and describe how excitation might initiate and spread in this myogenic smooth muscle. We then review each of the ion channels in the myometrium: L- and T-type Ca2+ channels, KATP (Kir6) channels, voltage-dependent K channels (Kv4, Kv7, and Kv11), twin-pore domain K channels (TASK, TREK), inward rectifier Kir7.1, Ca2+-activated K+ channels with large (KCNMA1, Slo1), small (KCNN1–3), and intermediate (KCNN4) conductance, Na-activated K channels (Slo2), voltage-gated (SCN) Na+ and Na+ leak channels, nonselective (NALCN) channels, the Na K-ATPase, and hyperpolarization-activated cation channels. We finish by assessing how three key hormones— oxytocin, estrogen, and progesterone—modulate and integrate excitability throughout gestation. Expected final online publication date for the Annual Review of Physiology, Volume 83 is February 10, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Potassium channels activated by GABAB agonists and serotonin in cultured hippocampal neurons

1994 ◽  
Vol 71 (6) ◽  
pp. 2570-2575 ◽  
Author(s):  
L. S. Premkumar ◽  
P. W. Gage
Keyword(s):  
Potassium Channels ◽  
Hippocampal Neurons ◽  
Single Channel ◽  
Gamma Aminobutyric Acid ◽  
Kinetic Behavior ◽  
Open Time ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
Channel Currents ◽  
Cultured Hippocampal Neurons

1. Single-channel currents were recorded in cell-attached patches on cultured hippocampal neurons in response to gamma-aminobutyric acid-B (GABAB) agonists or serotonin applied to the cell surface outside the patch area. 2. The channels activated by GABAB agonists and serotonin were potassium selective but had a different conductance and kinetic behavior. Channels activated by GABAB agonists had a higher conductance, longer open-time, and longer burst-length than channels activated by serotonin. 3. The kinetic behavior of channels activated by GABAB agonists varied with potential whereas channels activated by serotonin did not show voltage-dependent changes in kinetics. 4. In a few cell-attached patches, both types of channel were activated when the cell was exposed to GABA together with serotonin. 5. It was concluded that GABAB agonists and serotonin activate different potassium channels in the soma of cultured hippocampal neurons.

Internal and external TEA block in single cloned K+ channels

1991 ◽  
Vol 261 (4) ◽  
pp. C583-C590 ◽  
Author(s):  
G. E. Kirsch ◽  
M. Taglialatela ◽  
A. M. Brown
Keyword(s):  
Single Channel ◽  
Channel Structure ◽  
K Channel ◽  
Cdna Clones ◽  
K Channels ◽  
Open Time ◽  
Voltage Dependent ◽  
Internal Site ◽  
Channel Open Time ◽  
Single Channel Currents

Tetraethylammonium (TEA) has been used recently to probe natural and mutational variants of voltage-dependent K+ channels encoded by cDNA clones. Its usefulness as a probe of channel structure prompted us to examine the molecular mechanism by which TEA blocks single-channel currents in Xenopus oocytes expressing the rat brain K+ channel, RCK2. TEA at the intracellular surface of membrane patches decreased channel open time and increased the duration of closed intervals. Tetrapentylammonium had similar but more potent effects. Extracellular application of TEA caused an apparent reduction of single-channel amplitude. Block was slower at the high-affinity internal site than at the low-affinity external site. Internal TEA selectively blocks open K+ channels, and the voltage dependence of the block indicates that the binding site lies within the membrane electric field at a point 25% of the distance from the cytoplasmic margin. External TEA also interacts with the open channel but is less sensitive to membrane potential. The results indicate that the internal and external TEA binding sites define the inner and outer margins of the aqueous pore.

scholarly journals Effective gating charges per channel in voltage-dependent K+ and Ca2+ channels.

1996 ◽  
Vol 108 (3) ◽  
pp. 143-155 ◽  
Author(s):  
F Noceti ◽  
P Baldelli ◽  
X Wei ◽  
N Qin ◽  
L Toro ◽  
...  
Keyword(s):  
Ionic Current ◽  
Variance Analysis ◽  
Beta Subunit ◽  
Charge Movement ◽  
Gating Currents ◽  
Open Probability ◽  
K Channels ◽  
Voltage Dependent ◽  
Pore Opening ◽  
Ca2 Channels

In voltage-dependent ion channels, the gating of the channels is determined by the movement of the voltage sensor. This movement reflects the rearrangement of the protein in response to a voltage stimulus, and it can be thought of as a net displacement of elementary charges (e0) through the membrane (z: effective number of elementary charges). In this paper, we measured z in Shaker IR (inactivation removed) K+ channels, neuronal alpha 1E and alpha 1A, and cardiac alpha 1C Ca2+ channels using two methods: (a) limiting slope analysis of the conductance-voltage relationship and (b) variance analysis, to evaluate the number of active channels in a patch, combined with the measurement of charge movement in the same patch. We found that in Shaker IR K+ channels the two methods agreed with a z congruent to 13. This suggests that all the channels that gate can open and that all the measured charge is coupled to pore opening in a strictly sequential kinetic model. For all Ca2+ channels the limiting slope method gave consistent results regardless of the presence or type of beta subunit tested (z = 8.6). However, as seen with alpha 1E, the variance analysis gave different results depending on the beta subunit used. alpha 1E and alpha 1E beta 1a gave higher z values (z = 14.77 and z = 15.13 respectively) than alpha 1E beta 2a (z = 9.50, which is similar to the limiting slope results). Both the beta 1a and beta 2a subunits, coexpressed with alpha 1E Ca2+ channels facilitated channel opening by shifting the activation curve to more negative potentials, but only the beta 2a subunit increased the maximum open probability. The higher z using variance analysis in alpha 1E and alpha 1E beta 1a can be explained by a set of charges not coupled to pore opening. This set of charges moves in transitions leading to nulls thus not contributing to the ionic current fluctuations but eliciting gating currents. Coexpression of the beta 2a subunit would minimize the fraction of nulls leading to the correct estimation of the number of channels and z.

Modulation of maxi-K+ channels by voltage-dependent Ca2+ channels and methacholine in single airway myocytes

1997 ◽  
Vol 272 (4) ◽  
pp. C1151-C1159 ◽  
Author(s):  
Y. X. Wang ◽  
B. K. Fleischmann ◽  
M. I. Kotlikoff
Keyword(s):  
Outward Current ◽  
Cyclopiazonic Acid ◽  
Airway Smooth Muscle Cells ◽  
Strongly Coupled ◽  
K Channels ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Cell Current ◽  
The Mean ◽  
Ca2 Channels

The role of Ca2+ influx through voltage-dependent Ca2+ channels and the inhibitory effects of methacholine on large-conductance Ca2+-activated K+ (K(Ca)) channels (maxi-K+ channels) were studied in voltage-clamped (nystatin), fura 2-loaded airway smooth muscle cells. Spontaneous transient outward currents (STOCs) were strongly coupled to voltage-dependent Ca2+ channel activity; activity was suppressed by nisoldipine and Cd2+ and increased by BAY K 8644 within seconds. Moreover, release of intracellular Ca2+ by caffeine or cyclopiazonic acid only partially suppressed STOCs, and the remainder were almost completely blocked by nisoldipine. Methacholine suppressed STOCs but also significantly decreased the mean outward current. Whole cell current inhibition was observed in the presence of 4-aminopyridine but not in the presence of charybdotoxin. Caffeine inhibited STOCs but macroscopic outward currents were not altered. In the continued presence of caffeine, methacholine abolished the remaining STOCs and decreased the mean K+ current. We conclude that STOCs are activated by influx of Ca2+ through plasmalemmal voltage-dependent Ca2+ channels, as well as by release of Ca2+ from intracellular stores, and muscarinic stimulation depresses the mean K(Ca) current via a pathway independent of the depletion of intracellular Ca2+ stores.

scholarly journals Mg2+ Modulates Voltage-Dependent Activation in Ether-à-Go-Go Potassium Channels by Binding between Transmembrane Segments S2 and S3

2000 ◽  
Vol 116 (5) ◽  
pp. 663-678 ◽  
Author(s):  
William R. Silverman ◽  
Chih-Yung Tang ◽  
Allan F. Mock ◽  
Kyung-Bong Huh ◽  
Diane M. Papazian
Keyword(s):  
Potassium Channels ◽  
Binding Site ◽  
Voltage Sensor ◽  
Wild Type ◽  
Activation Kinetics ◽  
Fast Kinetics ◽  
K Channels ◽  
Transmembrane Segments ◽  
Acidic Residues ◽  
Voltage Dependent

Extracellular Mg2+ directly modulates voltage-dependent activation in ether-à-go-go (eag) potassium channels, slowing the kinetics of ionic and gating currents (Tang, C.-Y., F. Bezanilla, and D.M. Papazian. 2000. J. Gen. Physiol. 115:319-337). To exert its effect, Mg2+ presumably binds to a site in or near the eag voltage sensor. We have tested the hypothesis that acidic residues unique to eag family members, located in transmembrane segments S2 and S3, contribute to the Mg2+-binding site. Two eag-specific acidic residues and three acidic residues found in the S2 and S3 segments of all voltage-dependent K+ channels were individually mutated in Drosophila eag, mutant channels were expressed in Xenopus oocytes, and the effect of Mg2+ on ionic current kinetics was measured using a two electrode voltage clamp. Neutralization of eag-specific residues D278 in S2 and D327 in S3 eliminated Mg2+-sensitivity and mimicked the slowing of activation kinetics caused by Mg2+ binding to the wild-type channel. These results suggest that Mg2+ modulates activation kinetics in wild-type eag by screening the negatively charged side chains of D278 and D327. Therefore, these residues are likely to coordinate the bound ion. In contrast, neutralization of the widely conserved residues D284 in S2 and D319 in S3 preserved the fast kinetics seen in wild-type eag in the absence of Mg2+, indicating that D284 and D319 do not mediate the slowing of activation caused by Mg2+ binding. Mutations at D284 affected the eag gating pathway, shifting the voltage dependence of Mg2+-sensitive, rate limiting transitions in the hyperpolarized direction. Another widely conserved residue, D274 in S2, is not required for Mg2+ sensitivity but is in the vicinity of the binding site. We conclude that Mg2+ binds in a water-filled pocket between S2 and S3 and thereby modulates voltage-dependent gating. The identification of this site constrains the packing of transmembrane segments in the voltage sensor of K+ channels, and suggests a molecular mechanism by which extracellular cations modulate eag activation kinetics.

scholarly journals α-Latrotoxin Induces Exocytosis by Inhibition of Voltage-dependent K+Channels and by Stimulation of L-type Ca2+Channels via Latrophilin in β-Cells

2005 ◽  
Vol 281 (9) ◽  
pp. 5522-5531 ◽  
Author(s):  
Sophie Lajus ◽  
Pierre Vacher ◽  
Denise Huber ◽  
Mathilde Dubois ◽  
Marie-Noëlle Benassy ◽  
...  
Keyword(s):  
Β Cells ◽  
K Channels ◽  
Voltage Dependent ◽  
Ca2 Channels ◽  
Stimulation Of

An active membrane model of the cerebellar Purkinje cell. I. Simulation of current clamps in slice

1994 ◽  
Vol 71 (1) ◽  
pp. 375-400 ◽  
Author(s):  
E. De Schutter ◽  
J. M. Bower
Keyword(s):  
Purkinje Cell ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channels ◽  
Plateau Potentials ◽  
Spike Generation ◽  
K Channels ◽  
Voltage Dependent ◽  
P Type ◽  
Ca2 Channels

1. A detailed compartmental model of a cerebellar Purkinje cell with active dendritic membrane was constructed. The model was based on anatomic reconstructions of single Purkinje cells and included 10 different types of voltage-dependent channels described by Hodgkin-Huxley equations, derived from Purkinje cell-specific voltage-clamp data where available. These channels included a fast and persistent Na+ channel, three voltage-dependent K+ channels, T-type and P-type Ca2+ channels, and two types of Ca(2+)-activated K+ channels. 2. The ionic channels were distributed differentially over three zones of the model, with Na+ channels in the soma, fast K+ channels in the soma and main dendrite, and Ca2+ channels and Ca(2+)-activated K+ channels in the entire dendrite. Channel densities in the model were varied until it could reproduce Purkinje cell responses to current injections in the soma or dendrite, as observed in slice recordings. 3. As in real Purkinje cells, the model generated two types of spiking behavior. In response to small current injections the model fired exclusively fast somatic spikes. These somatic spikes were caused by Na+ channels and repolarized by the delayed rectifier. When higher-amplitude current injections were given, sodium spiking increased in frequency until the model generated large dendritic Ca2+ spikes. Analysis of membrane currents underlying this behavior showed that these Ca2+ spikes were caused by the P-type Ca2+ channel and repolarized by the BK-type Ca(2+)-activated K+ channel. As in pharmacological blocking experiments, removal of Na+ channels abolished the fast spikes and removal of Ca2+ channels removed Ca2+ spiking. 4. In addition to spiking behavior, the model also produced slow plateau potentials in both the dendrite and soma. These longer-duration potentials occurred in response to both short and prolonged current steps. Analysis of the model demonstrated that the plateau potentials in the soma were caused by the window current component of the fast Na+ current, which was much larger than the current through the persistent Na+ channels. Plateau potentials in the dendrite were carried by the same P-type Ca2+ channel that was also responsible for Ca2+ spike generation. The P channel could participate in both model functions because of the low-threshold K2-type Ca(2+)-activated K+ channel, which dynamically changed the threshold for dendritic spike generation through a negative feedback loop with the activation kinetics of the P-type Ca2+ channel. 5. These model responses were robust to changes in the densities of all of the ionic channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Local Anesthetics Modulate Neuronal Calcium Signaling through Multiple Sites of Action

2003 ◽  
Vol 98 (5) ◽  
pp. 1139-1146 ◽  
Author(s):  
Fang Xu ◽  
Zayra Garavito-Aguilar ◽  
Esperanza Recio-Pinto ◽  
Jin Zhang ◽  
Thomas J. J. Blanck
Keyword(s):  
Local Anesthetics ◽  
K Channel ◽  
Na Channels ◽  
Channel Blockade ◽  
K Channels ◽  
Voltage Dependent ◽  
Sites Of Action ◽  
A Site ◽  
Ca2 Channels

Background Local anesthetics (LAs) are known to inhibit voltage-dependent Na+ channels, as well as K+ and Ca2+ channels, but with lower potency. Since cellular excitability and responsiveness are largely determined by intracellular Ca2+ availability, sites along the Ca2+ signaling pathways may be targets of LAs. This study was aimed to investigate the LA effects on depolarization and receptor-mediated intracellular Ca2+ changes and to examine the role of Na+ and K+ channels in such functional responses. Methods Effects of bupivacaine, ropivacaine, mepivacaine, and lidocaine (0.1-2.3 mm) on evoked [Ca2+](i) transients were investigated in neuronal SH-SY5Y cell suspensions using Fura-2 as the intracellular Ca2+ indicator. Potassium chloride (KCl, 100 mm) and carbachol (1 mm) were individually or sequentially applied to evoke increases in intracellular Ca2+. Coapplication of LA and Na+/K+ channel blockers was used to evaluate the role of Na+ and K+ channels in the LA effect on the evoked [Ca2+](i) transients. Results All four LAs concentration-dependently inhibited both KCl- and carbachol-evoked [Ca2+](i) transients with the potency order bupivacaine > ropivacaine > lidocaine >/= mepivacaine. The carbachol-evoked [Ca2+](i) transients were more sensitive to LAs without than with a KCl prestimulation, whereas the LA-effect on the KCl-evoked [Ca2+](i) transients was not uniformly affected by a carbachol prestimulation. Na+ channel blockade did not alter the evoked [Ca2+](i) transients with or without a LA. In the absence of LA, K+ channel blockade increased the KCl-, but decreased the carbachol-evoked [Ca2+](i) transients. A coapplication of LA and K+ channel blocker resulted in larger inhibition of both KCl- and carbachol-evoked [Ca2+](i) transients than by LA alone. Conclusions Different and overlapping sites of action of LAs are involved in inhibiting the KCl- and carbachol-evoked [Ca2+](i) transients, including voltage-dependent Ca2+ channels, a site associated with the caffeine-sensitive Ca2+ store and a possible site associated with the IP(3)-sensitive Ca2+ store, and a site in the muscarinic pathway. K+ channels, but not Na+ channels, seem to modulate the evoked [Ca2+](i) transients, as well as the LA-effects on such responses.

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