scholarly journals Identification of an Ethanol Recognition Site in BK Beta1 Subunit that Mediates Ethanol-Induced Cerebral Artery Myocyte BK Channel Inhibition and the Resulting Artery Constriction

2018 ◽  
Vol 114 (3) ◽  
pp. 308a
Author(s):  
Guruprasad Kuntamallappanavar ◽  
Anna Bukiya ◽  
Alex Dopico
Keyword(s):  
Cerebral Artery ◽  
Bk Channel ◽  
Recognition Site ◽  
Channel Inhibition ◽  
Beta1 Subunit

scholarly journals BK channel inhibition by strong extracellular acidification

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Yu Zhou ◽  
Xiao-Ming Xia ◽  
Christopher J Lingle
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
Extracellular Acidification ◽  
Channel Inhibition ◽  
Wide Range ◽  
The Family ◽  
Voltage Dependent ◽  
Intracellular Organelles ◽  
Extracellular Side ◽  
Key Residues

Mammalian BK-type voltage- and Ca2+-dependent K+ channels are found in a wide range of cells and intracellular organelles. Among different loci, the composition of the extracellular microenvironment, including pH, may differ substantially. For example, it has been reported that BK channels are expressed in lysosomes with their extracellular side facing the strongly acidified lysosomal lumen (pH ~4.5). Here we show that BK activation is strongly and reversibly inhibited by extracellular H+, with its conductance-voltage relationship shifted by more than +100 mV at pHO 4. Our results reveal that this inhibition is mainly caused by H+ inhibition of BK voltage-sensor (VSD) activation through three acidic residues on the extracellular side of BK VSD. Given that these key residues (D133, D147, D153) are highly conserved among members in the voltage-dependent cation channel superfamily, the mechanism underlying BK inhibition by extracellular acidification might also be applicable to other members in the family.

scholarly journals Mechanism of BK Channel Inhibition by the Opioid Agonist Loperamide

2019 ◽  
Vol 116 (3) ◽  
pp. 543a
Author(s):  
Alexandre G. Vouga ◽  
Michael E. Rockman ◽  
Marlene A. Jacobson ◽  
Brad S. Rothberg
Keyword(s):  
Bk Channel ◽  
Opioid Agonist ◽  
Channel Inhibition

scholarly journals Novel Topology of BK Channel Beta1 Subunit Predicted on the Basis of the “Positive-Inside” Rule Points at an Intracellular Location of the Loop

2018 ◽  
Vol 114 (3) ◽  
pp. 480a
Author(s):  
Maria Simakova ◽  
Shivantika Bisen ◽  
Kelsey Cleland ◽  
Avia Rosenhouse-Dantsker ◽  
Alex Dopico ◽  
...  
Keyword(s):  
Bk Channel ◽  
Intracellular Location ◽  
Beta1 Subunit

Abstract 971: Inhibition Of Vascular Bk Channel Activity By Caveolae-mediated Angiotensin II Type I Receptor Signaling In Diabetic Vessels

Circulation ◽  
2007 ◽  
Vol 116 (suppl_16) ◽  
Author(s):  
Tong Lu ◽  
Xiaoli Wang ◽  
Hon-Chi Lee
Keyword(s):  
Angiotensin Ii ◽  
Tyrosine Kinases ◽  
Buoyant Density ◽  
Bk Channels ◽  
Bk Channel ◽  
Hek293 Cells ◽  
Type I ◽  
Ang Ii ◽  
Channel Activity ◽  
Channel Inhibition

Angiotensin II (Ang II) type I receptor (ATR 1 ) trafficking into caveolae is essential for Ang II signaling, which is known to be abnormal in diabetic vessels. We have shown that the large conductance Ca 2+ actviated K + (BK) channels are also targeted to caveolae in vascular cells. The potential interaction between Ang II signaling and BK channel function in normal and diabetic vessels is unknown. Using whole-cell patch clamp recordings and molecular biology techniques, we examined the mechanisms through which caveolae targeting facilitates the regulation of BK channels by Ang II signaling. We found that in cultured human coronary arterial smooth muscle cells (CASMC) and in freshly isolated rat CASMC, BK channels, ATR 1 , and Src-family protein tyrosine kinases (Src-PTK) were colocalized and enriched in the low buoyant density, caveolae-rich fractions. 2 μM Ang II inhibited BK channel activity by ∼50% in rat and human CASMC and these effects were completely abolished by 2 μM Losartan (a selective ATR 1 inhibitor), 10 μM PP2 (a selective Src-PTK inhibitor), and by caveolin-1 (cav-1) knockdown using 60 nM siRNA. Similar results were obtained in HEK293 cells coexpressing hSlo, BK-β 1 subunit, ATR 1 , cav-1, and Src-PTK, indicating that inhibition of BK channels by Ang II was mediated through ATR 1 activation of Src-PTK and the integrity of caveolae is critical for Ang II signaling. Culturing human CASMC with high glucose (HG, 22 mM) enhanced Ang II-mediated BK channel inhibition (78.8±16.8% vs. 54.5±15.7% in 5 mM glucose, n=3, p<0.05). Analysis of ATR 1 , Src-PTK, and BK channel distribution by sucrose gradient fractionation and by co-immunoprecipitation with anti-cav-1 antibodies showed that expression of ATR 1 and Src-PTK were up-regulated in human CASMC cultured in HG and in CASMC from streptozotocin-induced diabetic rats. Total BK channel protein in these cells was diminished, but the amount of BK channels co-immunoprecipitated with anti-cav-1 antibody was increased, suggesting increased caveolae targeting of BK channels in diabetes, which leads to enhanced Ang II-mediated BK channel inhibition. These results indicate that Ang II-BK channel interaction is critically dependent upon caveolae targeting under normal conditions and in disease states such as diabetes.

scholarly journals Reduced Ca2+ Spark Activity after Subarachnoid Hemorrhage Disables BK Channel Control of Cerebral Artery Tone

2010 ◽  
Vol 31 (1) ◽  
pp. 3-16 ◽  
Author(s):  
Masayo Koide ◽  
Matthew A Nystoriak ◽  
Gayathri Krishnamoorthy ◽  
Kevin P O'Connor ◽  
Adrian D Bonev ◽  
...  
Keyword(s):  
Subarachnoid Hemorrhage ◽  
Cerebral Artery ◽  
Laser Scanning ◽  
Single Channel ◽  
Cerebral Arteries ◽  
Laser Scanning Confocal Microscopy ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activity ◽  
Similar Reduction

Intracellular Ca2+ release events (‘Ca2+ sparks’) and transient activation of large-conductance Ca2+-activated potassium (BK) channels represent an important vasodilator pathway in the cerebral vasculature. Considering the frequent occurrence of cerebral artery constriction after subarachnoid hemorrhage (SAH), our objective was to determine whether Ca2+ spark and BK channel activity were reduced in cerebral artery myocytes from SAH model rabbits. Using laser scanning confocal microscopy, we observed ∼50% reduction in Ca2+ spark activity, reflecting a decrease in the number of functional Ca2+ spark discharge sites. Patch-clamp electrophysiology showed a similar reduction in Ca2+ spark-induced transient BK currents, without change in BK channel density or single-channel properties. Consistent with a reduction in active Ca2+ spark sites, quantitative real-time PCR and western blotting revealed decreased expression of ryanodine receptor type 2 (RyR-2) and increased expression of the RyR-2-stabilizing protein, FKBP12.6, in the cerebral arteries from SAH animals. Furthermore, inhibitors of Ca2+ sparks (ryanodine) or BK channels (paxilline) constricted arteries from control, but not from SAH animals. This study shows that SAH-induced decreased subcellular Ca2+ signaling events disable BK channel activity, leading to cerebral artery constriction. This phenomenon may contribute to decreased cerebral blood flow and poor outcome after aneurysmal SAH.

scholarly journals Glucose-mediated inhibition of calcium-activated potassium channels limits α-cell calcium influx and glucagon secretion

2019 ◽  
Vol 316 (4) ◽  
pp. E646-E659 ◽  
Author(s):  
Matthew T. Dickerson ◽  
Prasanna K. Dadi ◽  
Molly K. Altman ◽  
Kenneth R. Verlage ◽  
Ariel S. Thorson ◽  
...  
Keyword(s):  
Calcium Influx ◽  
Glucagon Secretion ◽  
Bk Channel ◽  
Prolonged Treatment ◽  
Channel Inhibition ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
Calcium Activated Potassium Channels ◽  
Low Glucose ◽  
Ik Channel

Pancreatic α-cells exhibit oscillations in cytosolic Ca2+ (Ca2+c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca2+c oscillations have not been elucidated. As β-cell Ca2+c oscillations are regulated in part by Ca2+-activated K+ (Kslow) currents, this work investigated the role of Kslow in α-cell Ca2+ handling and GCG secretion. α-Cells displayed Kslow currents that were dependent on Ca2+ influx through L- and P/Q-type voltage-dependent Ca2+ channels (VDCCs) as well as Ca2+ released from endoplasmic reticulum stores. α-Cell Kslow was decreased by small-conductance Ca2+-activated K+ (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca2+-activated K+ (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca2+-activated K+ (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell Kslow with apamin depolarized membrane potential ( Vm) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca2+ influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca2+ influx. Total α-cell Ca2+c was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca2+c following prolonged Kslow inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that Kslow activation provides a hyperpolarizing influence on α-cell Vm that sustains Ca2+ entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca2+c is elevated during secretagogue stimulation, Kslow activation helps to preserve GCG secretion.

scholarly journals Specificity of cholesterol and analogs to modulate BK channels points to direct sterol–channel protein interactions

2010 ◽  
Vol 137 (1) ◽  
pp. 93-110 ◽  
Author(s):  
Anna N. Bukiya ◽  
Jitendra D. Belani ◽  
Scott Rychnovsky ◽  
Alex M. Dopico
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
Lipid Monolayer ◽  
Lateral Stress ◽  
Molecular Area ◽  
Protein Surface ◽  
Ring Fusion ◽  
Α Subunit ◽  
Planar Conformation ◽  
Channel Inhibition

The activity (Po) of large-conductance voltage/Ca2+-gated K+ (BK) channels is blunted by cholesterol levels within the range found in natural membranes. We probed BK channel–forming α (cbv1) subunits in phospholipid bilayers with cholesterol and related monohydroxysterols and performed computational dynamics to pinpoint the structural requirements for monohydroxysterols to reduce BK Po and obtain insights into cholesterol’s mechanism of action. Cholesterol, cholestanol, and coprostanol reduced Po by shortening mean open and lengthening mean closed times, whereas epicholesterol, epicholestanol, epicoprostanol, and cholesterol trisnorcholenic acid were ineffective. Thus, channel inhibition by monohydroxysterols requires the β configuration of the C3 hydroxyl and is favored by the hydrophobic nature of the side chain, while having lax requirements on the sterol A/B ring fusion. Destabilization of BK channel open state(s) has been previously interpreted as reflecting increased bilayer lateral stress by cholesterol. Lateral stress is controlled by the sterol molecular area and lipid monolayer lateral tension, the latter being related to the sterol ability to adopt a planar conformation in lipid media. However, we found that the differential efficacies of monohydroxysterols to reduce Po (cholesterol≥coprostanol≥cholestanol&gt;&gt;&gt;epicholesterol) did not follow molecular area rank (coprostanol&gt;&gt;epicholesterol&gt;cholesterol&gt;cholestanol). In addition, computationally predicted energies for cholesterol (effective BK inhibitor) and epicholesterol (ineffective) to adopt a planar conformation were similar. Finally, cholesterol and coprostanol reduced Po, yet these sterols have opposite effects on tight lipid packing and, likely, on lateral stress. Collectively, these findings suggest that an increase in bilayer lateral stress is unlikely to underlie the differential ability of cholesterol and related steroids to inhibit BK channels. Remarkably, ent-cholesterol (cholesterol mirror image) failed to reduce Po, indicating that cholesterol efficacy requires sterol stereospecific recognition by a protein surface. The BK channel phenotype resembled that of α homotetramers. Thus, we hypothesize that a cholesterol-recognizing protein surface resides at the BK α subunit itself.

Concentration-dependent effects of cocaine on monoamine-induced constriction of cannulated, pressurized cerebral arteries from fetal sheep

1995 ◽  
Vol 7 (5) ◽  
pp. 1389
Author(s):  
MD Schreiber ◽  
JA Madden ◽  
RF Covert ◽  
MB Hershenson ◽  
LJ Torgerson
Keyword(s):  
Cerebral Artery ◽  
Cerebral Arteries ◽  
Na Channel ◽  
Monoamine Neurotransmitter ◽  
Response Curves ◽  
Fetal Sheep ◽  
Uptake Inhibition ◽  
Channel Inhibition ◽  
Vascular Responsiveness

Drugs, such as cocaine, which may alter monoamine neurotransmitter responsiveness, could adversely affect the regulation of cerebral vasculature. Cocaine exhibits at least two mechanisms that may alter vascular responsiveness: synaptic uptake inhibition, which may augment response to stimulation, and Na+ channel inhibition, which may attenuate response. To help elicit the concentration-dependent effects of cocaine, the effects of cocaine on monoamine neurotransmitter responsiveness were studied in vitro on fetal sheep cerebral arteries (120 days gestation). The changes in diameter of segments of cannulated, pressurized fetal sheep cerebral artery were measured with a videomicroscaler system. Cumulative concentration-response curves (10(-10) to 10(-4)M) were generated for two monoamines, norepinephrine and serotonin, alone and in the presence of cocaine (10(-5) or 10(-4)M). Cocaine caused concentration-dependent alteration of response. At 10(-4)M, cocaine attenuated mean maximal norepinephrine-induced vasoconstriction 46.2% (P < 0.05). At 10(-5)M, cocaine increased sensitivity to norepinephrine (log EC50 decreased -6.63 +/- 0.09 to -7.11 +/- 0.03) and to serotonin (log EC50 decreased -7.24 +/- 0.04 to -7.81 +/- 0.09) (P < 0.05). The higher concentration of cocaine (10(-4)M) did not significantly decrease log EC50 norepinephrine. Cocaine (10(-4)M) also attenuated the response to single doses of norepinephrine (10(-6)M) and serotonin (10(-6)M) by 26.5% and 40.0%, respectively (P < or = 0.05). It is concluded that cocaine has concentration-dependent effects on vasoconstriction of the fetal sheep cerebral artery in vitro. This cocaine-induced alteration of cerebral vascular responsiveness to monoamines may be important in the regulation of fetal cerebral blood flow.

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