scholarly journals Coronary Large Conductance Ca2+-Activated K+ Channel Dysfunction in Diabetes Mellitus

2021 ◽  
Vol 12 ◽  
Author(s):  
Tong Lu ◽  
Hon-Chi Lee
Keyword(s):  
Diabetes Mellitus ◽  
Vascular Tone ◽  
Microvascular Complications ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Organ Perfusion ◽  
Biophysical Properties ◽  
Diabetic Vasculopathy ◽  
Channel Expression

Diabetes mellitus (DM) is an independent risk of macrovascular and microvascular complications, while cardiovascular diseases remain a leading cause of death in both men and women with diabetes. Large conductance Ca2+-activated K+ (BK) channels are abundantly expressed in arteries and are the key ionic determinant of vascular tone and organ perfusion. It is well established that the downregulation of vascular BK channel function with reduced BK channel protein expression and altered intrinsic BK channel biophysical properties is associated with diabetic vasculopathy. Recent efforts also showed that diabetes-associated changes in signaling pathways and transcriptional factors contribute to the downregulation of BK channel expression. This manuscript will review our current understandings on the molecular, physiological, and biophysical mechanisms that underlie coronary BK channelopathy in diabetes mellitus.

scholarly journals Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

2014 ◽  
Vol 306 (5) ◽  
pp. C460-C470 ◽  
Author(s):  
Kiril L. Hristov ◽  
Amy C. Smith ◽  
Shankar P. Parajuli ◽  
John Malysz ◽  
Georgi V. Petkov
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Guinea Pig ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Channel Regulation ◽  
Pkc Activation

Large-conductance voltage- and Ca2+-activated K+ (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca2+ imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca2+ sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca2+ levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca2+-dependent mechanism, thus increasing DSM contractility.

scholarly journals Effect of aldosterone on BK channel expression in mammalian cortical collecting duct

2008 ◽  
Vol 295 (3) ◽  
pp. F780-F788 ◽  
Author(s):  
Genevieve Estilo ◽  
Wen Liu ◽  
Nuria Pastor-Soler ◽  
Phillip Mitchell ◽  
Marcelo D. Carattino ◽  
...  
Keyword(s):  
Splice Variants ◽  
Collecting Duct ◽  
Bk Channels ◽  
Bk Channel ◽  
Mrna Abundance ◽  
Cortical Collecting Duct ◽  
Α Subunit ◽  
Channel Expression ◽  
Tubular Flow ◽  
Circulating Levels

Apical large-conductance Ca2+-activated K+ (BK) channels in the cortical collecting duct (CCD) mediate flow-stimulated K+ secretion. Dietary K+ loading for 10–14 days leads to an increase in BK channel mRNA abundance, enhanced flow-stimulated K+ secretion in microperfused CCDs, and a redistribution of immunodetectable channels from an intracellular pool to the apical membrane (Najjar F, Zhou H, Morimoto T, Bruns JB, Li HS, Liu W, Kleyman TR, Satlin LM. Am J Physiol Renal Physiol 289: F922–F932, 2005). To test whether this adaptation was mediated by a K+-induced increase in aldosterone, New Zealand White rabbits were fed a low-Na+ (LS) or high-Na+ (HS) diet for 7–10 days to alter circulating levels of aldosterone but not serum K+ concentration. Single CCDs were isolated for quantitation of BK channel subunit (total, α-splice variants, β-isoforms) mRNA abundance by real-time PCR and measurement of net transepithelial Na+ (JNa) and K+ (JK) transport by microperfusion; kidneys were processed for immunolocalization of BK α-subunit by immunofluorescence microscopy. At the time of death, LS rabbits excreted no urinary Na+ and had higher circulating levels of aldosterone than HS animals. The relative abundance of BK α-, β2-, and β4-subunit mRNA and localization of immunodetectable α-subunit were similar in CCDs from LS and HS animals. In response to an increase in tubular flow rate from ∼1 to 5 nl·min−1·mm−1, the increase in JNa was greater in LS vs. HS rabbits, yet the flow-stimulated increase in JK was similar in both groups. These data suggest that aldosterone does not contribute to the regulation of BK channel expression/activity in response to dietary K+ loading.

scholarly journals Detrusor overactivity is associated with downregulation of large-conductance calcium- and voltage-activated potassium channel protein

2010 ◽  
Vol 298 (6) ◽  
pp. F1416-F1423 ◽  
Author(s):  
Shaohua Chang ◽  
Cristiano Mendes Gomes ◽  
Joseph A. Hypolite ◽  
James Marx ◽  
Jaber Alanzi ◽  
...  
Keyword(s):  
Detrusor Overactivity ◽  
Bladder Outlet Obstruction ◽  
Rabbit Model ◽  
Outlet Obstruction ◽  
Bk Channels ◽  
Bk Channel ◽  
Β Subunit ◽  
Α Subunit ◽  
Translational Study ◽  
Channel Expression

Large-conductance voltage- and calcium-activated potassium (BK) channels have been shown to play a role in detrusor overactivity (DO). The goal of this study was to determine whether bladder outlet obstruction-induced DO is associated with downregulation of BK channels and whether BK channels affect myosin light chain 20 (MLC20) phosphorylation in detrusor smooth muscle (DSM). Partial bladder outlet obstruction (PBOO) was surgically induced in male New Zealand White rabbits. The rabbit PBOO model shows decreased voided volumes and increased voiding frequency. DSM from PBOO rabbits also show enhanced spontaneous contractions compared with control. Both BK channel α- and β-subunits were significantly decreased in DSM from PBOO rabbits. Immunostaining shows BKβ mainly expressed in DSM, and its expression is much less in PBOO DSM compared with control DSM. Furthermore, a translational study was performed to see whether the finding discovered in the animal model can be translated to human patients. The urodynamic study demonstrates several overactive DSM contractions during the urine-filling stage in benign prostatic hyperplasia (BPH) patients with DO, while DSM is very quiet in BPH patients without DO. DSM biopsies revealed significantly less BK channel expression at both mRNA and protein levels. The degree of downregulation of the BK β-subunit was greater than that of the BK α-subunit, and the downregulation of BK was only associated with DO, not BPH. Finally, the small interference (si) RNA-mediated downregulation of the BK β-subunit was employed to study the effect of BK depletion on MLC20 phosphorylation. siRNA-mediated BK channel reduction was associated with an increased MLC20 phosphorylation level in cultured DSM cells. In summary, PBOO-induced DO is associated with downregulation of BK channel expression in the rabbit model, and this finding can be translated to human BPH patients with DO. Furthermore, downregulation of the BK channel may contribute to DO by increasing the basal level of MLC20 phosphorylation.

scholarly journals OSR1 and SPAK Sensitivity of Large-Conductance Ca2+ Activated K+ Channel

2016 ◽  
Vol 38 (4) ◽  
pp. 1652-1662 ◽  
Author(s):  
Bernat Elvira ◽  
Yogesh Singh ◽  
Jamshed Warsi ◽  
Carlos Munoz ◽  
Florian Lang
Keyword(s):  
Cell Volume ◽  
Volume Regulation ◽  
Cell Volume Regulation ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Xenopus Laevis Oocytes ◽  
Channel Activity ◽  
Wild Type ◽  
Constitutively Active

Background/Aims: The oxidative stress-responsive kinase 1 (OSR1) and the serine/threonine kinases SPAK (SPS1-related proline/alanine-rich kinase) are under the control of WNK (with-no-K [Lys]) kinases. OSR1 and SPAK participate in diverse functions including cell volume regulation and neuronal excitability. Cell volume and neuronal excitation are further modified by the large conductance Ca2+-activated K+ channels (maxi K+ channel or BK channels). An influence of OSR1 and/or SPAK on BK channel activity has, however, never been shown. The present study thus explored whether OSR1 and/or SPAK modify the activity of BK channels. Methods: cRNA encoding the Ca2+ insensitive BK channel mutant BKM513I+Δ899-903 was injected into Xenopus laevis oocytes without or with additional injection of cRNA encoding wild-type OSR1 or wild-type SPAK, constitutively active T185EOSR1, catalytically inactive D164AOSR1, constitutively active T233ESPAK or catalytically inactive D212ASPAK. K+ channel activity was measured utilizing dual electrode voltage clamp. Results: BK channel activity in BKM513I+Δ899-903 expressing oocytes was significantly decreased by co-expression of OSR1 or SPAK. The effect of wild-type OSR1/SPAK was mimicked by T185EOSR1 and T233ESPAK, but not by D164AOSR1 or D212ASPAK. Conclusions: OSR1 and SPAK suppress BK channels, an effect possibly contributing to cell volume regulation and neuroexcitability.

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 BK current contributions to action potentials across the first postnatal week reflect age dependent changes in BK current kinetics in rat hippocampal neurons

2019 ◽  
Author(s):  
Michael Hunsberger ◽  
Michelle Mynlieff
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Hippocampal Neurons ◽  
Expression Patterns ◽  
Bk Channels ◽  
Bk Channel ◽  
Action Potential Firing ◽  
Developmental Trends ◽  
Channel Expression ◽  
Old Rats

AbstractThe large conductance calcium-activated potassium (BK) channel is a critical regulator of neuronal action potential firing and follows two distinct trends in early postnatal development: an increase in total expression and a shift from the faster activating STREX isoform to the slower ZERO isoform. We analyzed the functional consequences of developmental trends in BK channel expression in hippocampal neurons isolated from neonatal rats aged one to seven days. Following overnight cultures, action potentials were recorded using whole-cell patch clamp electrophysiology. This population of neurons undergoes a steady increase in excitability during this time and the effect of blockade of BK channel activity with 100 nM iberiotoxin, changes as the neurons mature. BK currents contribute significantly more to single action potentials in neurons of one-day old rats (with BK blockade extending action potential duration by 0.46±0.12 ms) than in those of seven-day old rats (with BK blockade extending action potential duration by 0.17±0.05 ms). BK currents also contribute consistently to maintain firing rates in neurons of one-day old rats throughout extended action potential firing; BK blockade evenly depresses action potentials frequency across action potential trains. In neurons from seven-day old rats, BK blockade initially increases firing frequency and then progressively decreases frequency as firing continues, ultimately depressing neuronal firing rates to a greater extent than in the neurons from one day old animals. These results are consistent with a transition from low expression of a fast activating BK isoform (STREX) to high expression of a slower activating isoform (ZERO).New and NoteworthyThis work describes the early developmental trends of BK channel activity. Early developmental trends in expression of BK channels, both total expression and relative isoform expression, have been previously reported, but little work describes the effect of these changes in expression patterns on excitability. Here, we show that early changes in BK channel expression patterns lead to changes in the role of BK channels in determining the action potential waveform and neuronal excitability.

scholarly journals 14-3-3γ, a novel regulator of the large-conductance Ca2+-activated K+ channel

2020 ◽  
Vol 319 (1) ◽  
pp. F52-F62
Author(s):  
Shan Chen ◽  
Xiuyan Feng ◽  
Xinxin Chen ◽  
Zhizhi Zhuang ◽  
Jia Xiao ◽  
...  
Keyword(s):  
Protein Expression ◽  
Specific Inhibitor ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Channel Activity ◽  
Open Probability ◽  
Protein Ubiquitination ◽  
293 Cells

14-3-3γ is a small protein regulating its target proteins through binding to phosphorylated serine/threonine residues. Sequence analysis of large-conductance Ca2+-activated K+ (BK) channels revealed a putative 14-3-3 binding site in the COOH-terminal region. Our previous data showed that 14-3-3γ is widely expressed in the mouse kidney. Therefore, we hypothesized that 14-3-3γ has a novel role in the regulation of BK channel activity and protein expression. We used electrophysiology, Western blot analysis, and coimmunoprecipitation to examine the effects of 14-3-3γ on BK channels both in vitro and in vivo. We demonstrated the interaction of 14-3-3γ with BK α-subunits (BKα) by coimmunoprecipitation. In human embryonic kidney-293 cells stably expressing BKα, overexpression of 14-3-3γ significantly decreased BK channel activity and channel open probability. 14-3-3γ inhibited both total and cell surface BKα protein expression while enhancing ERK1/2 phosphorylation in Cos-7 cells cotransfected with flag-14-3-3γ and myc-BK. Knockdown of 14-3-3γ by siRNA transfection markedly increased BKα expression. Blockade of the ERK1/2 pathway by incubation with the MEK-specific inhibitor U0126 partially abolished 14-3-3γ-mediated inhibition of BK protein expression. Similarly, pretreatment of the lysosomal inhibitor bafilomycin A1 reversed the inhibitory effects of 14-3-3γ on BK protein expression. Furthermore, overexpression of 14-3-3γ significantly increased BK protein ubiquitination in embryonic kidney-293 cells stably expressing BKα. Additionally, 3 days of dietary K+ challenge reduced 14-3-3γ expression and ERK1/2 phosphorylation while enhancing renal BK protein expression and K+ excretion. These data suggest that 14-3-3γ modulates BK channel activity and protein expression through an ERK1/2-mediated ubiquitin-lysosomal pathway.

Abstract 376: Nedd4 Regulated Bk Channels in Diabetes Mellitus

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
DAI-MIN ZHANG ◽  
Shao-liang Chen ◽  
Yanrong Zhu ◽  
Peng Ye
Keyword(s):  
Diabetes Mellitus ◽  
Current Density ◽  
Knockout Mice ◽  
Vascular Function ◽  
Critical Role ◽  
Vascular Diseases ◽  
Bk Channels ◽  
Bk Channel ◽  
Hek293 Cells ◽  
Kinetic Properties

Big conductance calcium activated potassium(BK) channel plays a critical role in pathophysiological regulation of vascular function. Recent studies indicated that the expression reduction of BK channels in high glucose condition exacerbated vessel dilation, and led to coronary artery diseases, while BK channel expression was reserved in A-kinase anchoring protein(AKAP) knockout mice at same condition. Here, We are to investigate heterologous co-expression of Nedd4 ligase, ubiquitin protein ligase, and KCa1.1 in HEK293 cells. The result shown that co-expression reduced BK current density without modulation of kinetic properties as measured by path clamp techniques. Modulation of current density was dependent on ligase activity and was lost in AKAP knockout mice with diabetes mellitus. Taken together, our data disclose a novel mechanism of KCa1.1 channel regulation that NEDD4 decreased BK channels expression in diabetes mellitus depending on AKAP signal complexity. These findings provide a new insight into potential therapeutic target in vascular diseases, especially in diabetes mellitus.This work was supported by the National Natural Science Foundation of China(Grant No. 8137034)

scholarly journals AKAP150 Contributes to Enhanced Vascular Tone by Facilitating Large-Conductance Ca 2+ -Activated K + Channel Remodeling in Hyperglycemia and Diabetes Mellitus

2014 ◽  
Vol 114 (4) ◽  
pp. 607-615 ◽  
Author(s):  
Matthew A. Nystoriak ◽  
Madeline Nieves-Cintrón ◽  
Patrick J. Nygren ◽  
Simon A. Hinke ◽  
C. Blake Nichols ◽  
...  
Keyword(s):  
Diabetes Mellitus ◽  
High Fat Diet ◽  
Vascular Tone ◽  
Scaffolding Protein ◽  
K Channel ◽  
High Fat ◽  
Activated T Cells ◽  
Genetic Ablation ◽  
Channel Function ◽  
Arterial Blood

Rationale : Increased contractility of arterial myocytes and enhanced vascular tone during hyperglycemia and diabetes mellitus may arise from impaired large-conductance Ca 2+ -activated K + (BK Ca ) channel function. The scaffolding protein A-kinase anchoring protein 150 (AKAP150) is a key regulator of calcineurin (CaN), a phosphatase known to modulate the expression of the regulatory BK Ca β1 subunit. Whether AKAP150 mediates BK Ca channel suppression during hyperglycemia and diabetes mellitus is unknown. Objective : To test the hypothesis that AKAP150-dependent CaN signaling mediates BK Ca β1 downregulation and impaired vascular BK Ca channel function during hyperglycemia and diabetes mellitus. Methods and Results : We found that AKAP150 is an important determinant of BK Ca channel remodeling, CaN/nuclear factor of activated T-cells c3 (NFATc3) activation, and resistance artery constriction in hyperglycemic animals on high-fat diet. Genetic ablation of AKAP150 protected against these alterations, including augmented vasoconstriction. d -glucose–dependent suppression of BK Ca channel β1 subunits required Ca 2+ influx via voltage-gated L-type Ca 2+ channels and mobilization of a CaN/NFATc3 signaling pathway. Remarkably, high-fat diet mice expressing a mutant AKAP150 unable to anchor CaN resisted activation of NFATc3 and downregulation of BK Ca β1 subunits and attenuated high-fat diet–induced elevation in arterial blood pressure. Conclusions : Our results support a model whereby subcellular anchoring of CaN by AKAP150 is a key molecular determinant of vascular BK Ca channel remodeling, which contributes to vasoconstriction during diabetes mellitus.

scholarly journals Inhibition of Ca2+-activated large-conductance K+ channel activity alters synaptic AMPA receptor phenotype in mouse cerebellar stellate cells

2011 ◽  
Vol 106 (1) ◽  
pp. 144-152 ◽  
Author(s):  
Yu Liu ◽  
Iaroslav Savtchouk ◽  
Shoana Acharjee ◽  
Siqiong June Liu
Keyword(s):  
Potassium Channels ◽  
Action Potential ◽  
Action Potential Duration ◽  
Action Potentials ◽  
Channel Blocker ◽  
Stellate Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Duration Of Action

Many fast-spiking inhibitory interneurons, including cerebellar stellate cells, fire brief action potentials and express α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptors (AMPAR) that are permeable to Ca2+ and do not contain the GluR2 subunit. In a recent study, we found that increasing action potential duration promotes GluR2 gene transcription in stellate cells. We have now tested the prediction that activation of potassium channels that control the duration of action potentials can suppress the expression of GluR2-containing AMPARs at stellate cell synapses. We find that large-conductance Ca2+-activated potassium (BK) channels mediate a large proportion of the depolarization-evoked noninactivating potassium current in stellate cells. Pharmacological blockade of BK channels prolonged the action potential duration in postsynaptic stellate cells and altered synaptic AMPAR subtype from GluR2-lacking to GluR2-containing Ca2+-impermeable AMPARs. An L-type channel blocker abolished an increase in Ca2+ entry that was associated with spike broadening and also prevented the BK channel blocker-induced switch in AMPAR phenotype. Thus blocking BK potassium channels prolongs the action potential duration and increases the expression of GluR2-containing receptors at the synapse by enhancing Ca2+ entry in cerebellar stellate cells.

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