scholarly journals Revisiting the Large-Conductance Calcium-Activated Potassium (BKCa) Channels in the Pulmonary Circulation

Biomolecules ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1629
Author(s):  
Divya Guntur ◽  
Horst Olschewski ◽  
Péter Enyedi ◽  
Réka Csáki ◽  
Andrea Olschewski ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Potassium Channels ◽  
Pulmonary Circulation ◽  
Hypoxic Pulmonary Vasoconstriction ◽  
Free Calcium ◽  
Bkca Channel ◽  
Lung Pathology ◽  
Open Probability ◽  
Bkca Channels ◽  
Genes Encoding

Potassium ion concentrations, controlled by ion pumps and potassium channels, predominantly govern a cell′s membrane potential and the tone in the vessels. Calcium-activated potassium channels respond to two different stimuli-changes in voltage and/or changes in intracellular free calcium. Large conductance calcium-activated potassium (BKCa) channels assemble from pore forming and various modulatory and auxiliary subunits. They are of vital significance due to their very high unitary conductance and hence their ability to rapidly cause extreme changes in the membrane potential. The pathophysiology of lung diseases in general and pulmonary hypertension, in particular, show the implication of either decreased expression and partial inactivation of BKCa channel and its subunits or mutations in the genes encoding different subunits of the channel. Signaling molecules, circulating humoral molecules, vasorelaxant agents, etc., have an influence on the open probability of the channel in pulmonary arterial vascular cells. BKCa channel is a possible therapeutic target, aimed to cause vasodilation in constricted or chronically stiffened vessels, as shown in various animal models. This review is a comprehensive collation of studies on BKCa channels in the pulmonary circulation under hypoxia (hypoxic pulmonary vasoconstriction; HPV), lung pathology, and fetal to neonatal transition, emphasising pharmacological interventions as viable therapeutic options.

scholarly journals The β1 Subunit Enhances Oxidative Regulation of Large-Conductance Calcium-activated K+ Channels

2004 ◽  
Vol 124 (4) ◽  
pp. 357-370 ◽  
Author(s):  
Lindsey Ciali Santarelli ◽  
Jianguo Chen ◽  
Stefan H. Heinemann ◽  
Toshinori Hoshi
Keyword(s):  
Bkca Channel ◽  
Open Probability ◽  
Bkca Channels ◽  
Additional Increase ◽  
Channel Activation ◽  
Α Subunit ◽  
Voltage Range ◽  
Virtual Absence ◽  
Methionine Residues ◽  
Oxidative Regulation

Oxidative stress may alter the functions of many proteins including the Slo1 large conductance calcium-activated potassium channel (BKCa). Previous results demonstrated that in the virtual absence of Ca2+, the oxidant chloramine-T (Ch-T), without the involvement of cysteine oxidation, increases the open probability and slows the deactivation of BKCa channels formed by human Slo1 (hSlo1) α subunits alone. Because native BKCa channel complexes may include the auxiliary subunit β1, we investigated whether β1 influences the oxidative regulation of hSlo1. Oxidation by Ch-T with β1 present shifted the half-activation voltage much further in the hyperpolarizing direction (−75 mV) as compared with that with α alone (−30 mV). This shift was eliminated in the presence of high [Ca2+]i, but the increase in open probability in the virtual absence of Ca2+ remained significant at physiologically relevant voltages. Furthermore, the slowing of channel deactivation after oxidation was even more dramatic in the presence of β1. Oxidation of cysteine and methionine residues within β1 was not involved in these potentiated effects because expression of mutant β1 subunits lacking cysteine or methionine residues produced results similar to those with wild-type β1. Unlike the results with α alone, oxidation by Ch-T caused a significant acceleration of channel activation only when β1 was present. The β1 M177 mutation disrupted normal channel activation and prevented the Ch-T–induced acceleration of activation. Overall, the functional effects of oxidation of the hSlo1 pore-forming α subunit are greatly amplified by the presence of β1, which leads to the additional increase in channel open probability and the slowing of deactivation. Furthermore, M177 within β1 is a critical structural determinant of channel activation and oxidative sensitivity. Together, the oxidized BKCa channel complex with β1 has a considerable chance of being open within the physiological voltage range even at low [Ca2+]i.

scholarly journals BKCa channel activation increases cardiac contractile recovery following hypothermic ischemia/reperfusion

2015 ◽  
Vol 309 (4) ◽  
pp. H625-H633 ◽  
Author(s):  
Brenda Cordeiro ◽  
Dmitry Terentyev ◽  
Richard T. Clements
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Mitochondrial Membrane ◽  
Left Ventricular ◽  
Bkca Channel ◽  
Ros Generation ◽  
H9c2 Cells ◽  
Bkca Channels ◽  
Channel Activation

Mitochondrial Ca2+-activated large-conductance K+ (BKCa) channels are thought to provide protection during ischemic insults in the heart. Rottlerin (mallotoxin) has been implicated as a potent BKCa activator. The purpose of this study was twofold: 1) to investigate the efficacy of BKCa channel activation as a cardioprotective strategy during ischemic cardioplegic arrest and reperfusion (CP/R) and 2) to assess the specificity of rottlerin for BKCa channels. Wild-type (WT) and BKCa knockout (KO) mice were subjected to an isolated heart model of ischemic CP/R. A mechanism of rottlerin-induced cardioprotection was also investigated using H9c2 cells subjected to in vitro CP/reoxygenation and assessed for mitochondrial membrane potential and reactive oxygen species (ROS) production. CP/R decreased left ventricular developed pressure, positive and negative first derivatives of left ventricular pressure, and coronary flow (CF) in WT mice. Rottlerin dose dependently increased the recovery of left ventricular function and CF to near baseline levels. BKCa KO hearts treated with or without 500 nM rottlerin were similar to WT CP hearts. H9c2 cells subjected to in vitro CP/R displayed reduced mitochondrial membrane potential and increased ROS generation, both of which were significantly normalized by rottlerin. We conclude that activation of BKCa channels rescues ischemic damage associated with CP/R, likely via effects on improved mitochondrial membrane potential and reduced ROS generation.

scholarly journals Effects of Bepridil on Stretch-Activated BKca Channels and Stretch-Induced Extrasystoles in Isolated Chick Hearts

2017 ◽  
pp. 459-465 ◽  
Author(s):  
H. JIN ◽  
G. IRIBE ◽  
K. NARUSE
Keyword(s):  
Membrane Potential ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Heart Rhythm ◽  
Channel Activity ◽  
Open Probability ◽  
Bkca Channels ◽  
Chick Heart ◽  
Lv Volume ◽  
Stretch Activated Channels

Various types of mechanosensitive ion channels, including cationic stretch-activated channels (SACNS) and stretch-activated BKca (SAKca) channels, modulate heart rhythm. Bepridil has been used as an antiarrhythmic drug with multiple pharmacological effects; however, whether it is effective for mechanically induced arrhythmia has not been well investigated. To test the effects of Bepridil on SAKca channels activity, cultured chick embryonic ventricular myocytes were used for single-channel recordings. Bepridil significantly reduced the open probability of the SAKca channel (PO). Next, to test the effects of bepridil on stretch-induced extrasystoles (SIE), we used an isolated 2-week-old Langendorff-perfused chick heart. The left ventricle (LV) volume was rapidly changed, and the probability of SIE was calculated in the presence and absence of bepridil, and the effect of the drug was compared with that of Gadolinium (Gd3+). Bepridil decreased the probability of SIE despite its suppressive effects on SAKca channel activity. The effects of Gd3+, which blocks both SAKca and SACNS, on the probability of SIE were the same as those of bepridil. Our results suggest that bepridil blocks not only SAKca channels but possibly also blocks SACNS, and thus decreases the stretch-induced cation influx (stabilizing membrane potential) to compensate and override the effects of the decrease in outward SAKca current (destabilizing membrane potential).

scholarly journals Mitochondrial potassium channels: A novel calcitriol target

2022 ◽  
Vol 27 (1) ◽  
Author(s):  
Anna M. Olszewska ◽  
Adam K. Sieradzan ◽  
Piotr Bednarczyk ◽  
Adam Szewczyk ◽  
Michał A. Żmijewski
Keyword(s):  
Vitamin D ◽  
Potassium Channels ◽  
Potassium Channel ◽  
Mitochondrial Membrane ◽  
Human Keratinocytes ◽  
Inner Mitochondrial Membrane ◽  
Open Probability ◽  
Expression Of Genes ◽  
High Calcium ◽  
Genes Encoding

Abstract Background Calcitriol (an active metabolite of vitamin D) modulates the expression of hundreds of human genes by activation of the vitamin D nuclear receptor (VDR). However, VDR-mediated transcriptional modulation does not fully explain various phenotypic effects of calcitriol. Recently a fast non-genomic response to vitamin D has been described, and it seems that mitochondria are one of the targets of calcitriol. These non-classical calcitriol targets open up a new area of research with potential clinical applications. The goal of our study was to ascertain whether calcitriol can modulate mitochondrial function through regulation of the potassium channels present in the inner mitochondrial membrane. Methods The effects of calcitriol on the potassium ion current were measured using the patch-clamp method modified for the inner mitochondrial membrane. Molecular docking experiments were conducted in the Autodock4 program. Additionally, changes in gene expression were investigated by qPCR, and transcription factor binding sites were analyzed in the CiiiDER program. Results For the first time, our results indicate that calcitriol directly affects the activity of the mitochondrial large-conductance Ca2+-regulated potassium channel (mitoBKCa) from the human astrocytoma (U-87 MG) cell line but not the mitochondrial calcium-independent two-pore domain potassium channel (mitoTASK-3) from human keratinocytes (HaCaT). The open probability of the mitoBKCa channel in high calcium conditions decreased after calcitriol treatment and the opposite effect was observed in low calcium conditions. Moreover, using the AutoDock4 program we predicted the binding poses of calcitriol to the calcium-bound BKCa channel and identified amino acids interacting with the calcitriol molecule. Additionally, we found that calcitriol influences the expression of genes encoding potassium channels. Such a dual, genomic and non-genomic action explains the pleiotropic activity of calcitriol. Conclusions Calcitriol can regulate the mitochondrial large-conductance calcium-regulated potassium channel. Our data open a new chapter in the study of non-genomic responses to vitamin D with potential implications for mitochondrial bioenergetics and cytoprotective mechanisms.

The Mechanism(s) of Hypoxic Pulmonary Vasoconstriction: Potassium Channels, Redox O2 Sensors, and Controversies

Physiology ◽  
2002 ◽  
Vol 17 (4) ◽  
pp. 131-137 ◽  
Author(s):  
Stephen Archer ◽  
Evangelos Michelakis
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Potassium Channels ◽  
Pulmonary Artery ◽  
Smooth Muscle Cell ◽  
Muscle Cell ◽  
Hypoxic Pulmonary Vasoconstriction ◽  
Pulmonary Vasoconstriction ◽  
Pulmonary Artery Smooth Muscle

Hypoxic pulmonary vasoconstriction matches perfusion to ventilation and optimizes systemic oxygenation. Alterations in Po2 are sensed by a vascular redox O2 sensor in the pulmonary artery smooth muscle cell, probably within the mitochondria. This creates a signal that modulates redox-sensitive K+ channels, thereby controlling membrane potential, Ca2+ entry, and tone.

scholarly journals The RCK1 domain of the human BKCa channel transduces Ca2+ binding into structural rearrangements

2010 ◽  
Vol 136 (2) ◽  
pp. 189-202 ◽  
Author(s):  
Taleh Yusifov ◽  
Anoosh D. Javaherian ◽  
Antonios Pantazis ◽  
Chris S. Gandhi ◽  
Riccardo Olcese
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Molecular Mechanism ◽  
Conformational Changes ◽  
Bkca Channel ◽  
Structural Rearrangements ◽  
Bkca Channels ◽  
Time Resolved ◽  
High Affinity ◽  
Cytosolic Domains

Large-conductance voltage- and Ca2+-activated K+ (BKCa) channels play a fundamental role in cellular function by integrating information from their voltage and Ca2+ sensors to control membrane potential and Ca2+ homeostasis. The molecular mechanism of Ca2+-dependent regulation of BKCa channels is unknown, but likely relies on the operation of two cytosolic domains, regulator of K+ conductance (RCK)1 and RCK2. Using solution-based investigations, we demonstrate that the purified BKCa RCK1 domain adopts an α/β fold, binds Ca2+, and assembles into an octameric superstructure similar to prokaryotic RCK domains. Results from steady-state and time-resolved spectroscopy reveal Ca2+-induced conformational changes in physiologically relevant [Ca2+]. The neutralization of residues known to be involved in high-affinity Ca2+ sensing (D362 and D367) prevented Ca2+-induced structural transitions in RCK1 but did not abolish Ca2+ binding. We provide evidence that the RCK1 domain is a high-affinity Ca2+ sensor that transduces Ca2+ binding into structural rearrangements, likely representing elementary steps in the Ca2+-dependent activation of human BKCa channels.

scholarly journals Similar Enhancement of BKCa Channel Function Despite Different Aerobic Exercise Frequency in Aging Cerebrovascular Myocytes

2016 ◽  
pp. 447-459 ◽  
Author(s):  
N. LI ◽  
B. LIU ◽  
S. XIANG ◽  
L. SHI
Keyword(s):  
Aerobic Exercise ◽  
Aerobic Exercise Training ◽  
Bkca Channel ◽  
Voltage Sensitivity ◽  
Open Probability ◽  
Exercise Frequency ◽  
Bkca Channels ◽  
Functional Changes ◽  
Young Rats ◽  
Training Frequency

Aerobic exercise showed beneficial influence on cardiovascular systems in aging, and mechanisms underlying vascular adaption remain unclear. Large-conductance Ca2+-activated K+ (BKCa) channels play critical roles in regulating cellular excitability and vascular tone. This study determined the effects of aerobic exercise on aging-associated functional changes in BKCa channels in cerebrovascular myocytes, Male Wistar rats aged 20-22 months were randomly assigned to sedentary (O-SED), low training frequency (O-EXL), and high training frequency group (O-EXH). Young rats were used as control. Compared to young rats, whole-cell BKCa current was decreased, and amplitude of spontaneous transient outward currents were reduced. The open probability and Ca2+/voltage sensitivity of single BKCa channel were declined in O-SED, accompanied with a reduction of tamoxifen-induced BKCa activation; the mean open time of BKCa channels was shortened whereas close time was prolonged. Aerobic exercise training markedly alleviated the aging-associated decline independent of training frequency. Exercise three times rather than five times weekly may be a time and cost-saving training volume required to offer beneficial effects to offset the functional declines of BKCa during aging.

scholarly journals Identification of the Large-Conductance Ca2+-Regulated Potassium Channel in Mitochondria of Human Bronchial Epithelial Cells

Molecules ◽  
2021 ◽  
Vol 26 (11) ◽  
pp. 3233
Author(s):  
Aleksandra Sek ◽  
Rafal P. Kampa ◽  
Bogusz Kulawiak ◽  
Adam Szewczyk ◽  
Piotr Bednarczyk
Keyword(s):  
Potassium Channels ◽  
Potassium Channel ◽  
Epithelial Cell Line ◽  
Bkca Channel ◽  
Channel Activity ◽  
Potassium Channel Opener ◽  
Patch Clamp Technique ◽  
Bkca Channels ◽  
Bronchial Epithelial ◽  
Channel Opener

Mitochondria play a key role in energy metabolism within the cell. Potassium channels such as ATP-sensitive, voltage-gated or large-conductance Ca2+-regulated channels have been described in the inner mitochondrial membrane. Several hypotheses have been proposed to describe the important roles of mitochondrial potassium channels in cell survival and death pathways. In the current study, we identified two populations of mitochondrial large-conductance Ca2+-regulated potassium (mitoBKCa) channels in human bronchial epithelial (HBE) cells. The biophysical properties of the channels were characterized using the patch-clamp technique. We observed the activity of the channel with a mean conductance close to 285 pS in symmetric 150/150 mM KCl solution. Channel activity was increased upon application of the potassium channel opener NS11021 in the micromolar concentration range. The channel activity was completely inhibited by 1 µM paxilline and 300 nM iberiotoxin, selective inhibitors of the BKCa channels. Based on calcium and iberiotoxin modulation, we suggest that the C-terminus of the protein is localized to the mitochondrial matrix. Additionally, using RT-PCR, we confirmed the presence of α pore-forming (Slo1) and auxiliary β3-β4 subunits of BKCa channel in HBE cells. Western blot analysis of cellular fractions confirmed the mitochondrial localization of α pore-forming and predominately β3 subunits. Additionally, the regulation of oxygen consumption and membrane potential of human bronchial epithelial mitochondria in the presence of the potassium channel opener NS11021 and inhibitor paxilline were also studied. In summary, for the first time, the electrophysiological and functional properties of the mitoBKCa channel in a bronchial epithelial cell line were described.

scholarly journals Effective Activation of BKCa Channels by QO-40 (5-(Chloromethyl)-3-(Naphthalen-1-yl)-2-(Trifluoromethyl)Pyrazolo [1,5-a]pyrimidin-7(4H)-one), Known to Be an Opener of KCNQ2/Q3 Channels

2021 ◽  
Vol 14 (5) ◽  
pp. 388
Author(s):  
Wei-Ting Chang ◽  
Sheng-Nan Wu
Keyword(s):  
Single Channel ◽  
Slow Component ◽  
Ionic Channel ◽  
Gh3 Cells ◽  
Bkca Channel ◽  
Bkca Channels ◽  
Gating Charge ◽  
Ramp Voltage ◽  
K Current ◽  
The Mean

QO-40 (5-(chloromethyl)-3-(naphthalene-1-yl)-2-(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-7(4H)-one) is a novel and selective activator of KCNQ2/KCNQ3 K+ channels. However, it remains largely unknown whether this compound can modify any other type of plasmalemmal ionic channel. The effects of QO-40 on ion channels in pituitary GH3 lactotrophs were investigated in this study. QO-40 stimulated Ca2+-activated K+ current (IK(Ca)) with an EC50 value of 2.3 μM in these cells. QO-40-stimulated IK(Ca) was attenuated by the further addition of GAL-021 or paxilline but not by linopirdine or TRAM-34. In inside-out mode, this compound added to the intracellular leaflet of the detached patches stimulated large-conductance Ca2+-activated K+ (BKCa) channels with no change in single-channel conductance; however, there was a decrease in the slow component of the mean closed time of BKCa channels. The KD value required for the QO-40-mediated decrease in the slow component at the mean closure time was 1.96 μM. This compound shifted the steady-state activation curve of BKCa channels to a less positive voltage and decreased the gating charge of the channel. The application of QO-40 also increased the hysteretic strength of BKCa channels elicited by a long-lasting isosceles-triangular ramp voltage. In HEK293T cells expressing α-hSlo, QO-40 stimulated BKCa channel activity. Overall, these findings demonstrate that QO-40 can interact directly with the BKCa channel to increase the amplitude of IK(Ca) in GH3 cells.

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