scholarly journals Depressed neuromuscular transmission causes weakness in mice lacking BK potassium channels

2020 ◽  
Vol 152 (5) ◽  
Author(s):  
Xueyong Wang ◽  
Steven R.A. Burke ◽  
Robert J. Talmadge ◽  
Andrew A. Voss ◽  
Mark M. Rich
Keyword(s):  
Action Potentials ◽  
Neuromuscular Transmission ◽  
Muscle Force ◽  
Bk Channels ◽  
Bk Channel ◽  
Motor Deficits ◽  
Muscle Stimulation ◽  
Vesicle Release ◽  
K Current

Mice lacking functional large-conductance voltage- and Ca2+-activated K+ channels (BK channels) are viable but have motor deficits including ataxia and weakness. The cause of weakness is unknown. In this study, we discovered, in vivo, that skeletal muscle in mice lacking BK channels (BK−/−) was weak in response to nerve stimulation but not to direct muscle stimulation, suggesting a failure of neuromuscular transmission. Voltage-clamp studies of the BK−/− neuromuscular junction (NMJ) revealed a reduction in evoked endplate current amplitude and the frequency of spontaneous vesicle release compared with WT littermates. Responses to 50-Hz stimulation indicated a reduced probability of vesicle release in BK−/− mice, suggestive of lower presynaptic Ca2+ entry. Pharmacological block of BK channels in WT NMJs did not affect NMJ function, surprisingly suggesting that the reduced vesicle release in BK−/− NMJs was not due to loss of BK channel–mediated K+ current. Possible explanations for our data include an effect of BK channels on development of the NMJ, a role for BK channels in regulating presynaptic Ca2+ current or the effectiveness of Ca2+ in triggering release. Consistent with reduced Ca2+ entry or effectiveness of Ca2+ in triggering release, use of 3,4-diaminopyridine to widen action potentials normalized evoked release in BK−/− mice to WT levels. Intraperitoneal application of 3,4-diaminopyridine fully restored in vivo nerve-stimulated muscle force in BK−/− mice. Our work demonstrates that mice lacking BK channels have weakness due to a defect in vesicle release at the NMJ.

Disruption of TRPV1-mediated coupling of coronary blood flow to cardiac metabolism in diabetic mice: role of nitric oxide and BK channels

2012 ◽  
Vol 303 (2) ◽  
pp. H216-H223 ◽  
Author(s):  
Giacinta Guarini ◽  
Vahagn A. Ohanyan ◽  
John G. Kmetz ◽  
Daniel J. DelloStritto ◽  
Roslin J. Thoppil ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Coronary Blood Flow ◽  
Cardiac Metabolism ◽  
Bk Channels ◽  
Bk Channel ◽  
Transient Receptor Potential Vanilloid ◽  
Trpv1 Channels ◽  
Channel Dependent

We have previously shown transient receptor potential vanilloid subtype 1 (TRPV1) channel-dependent coronary function is compromised in pigs with metabolic syndrome (MetS). However, the mechanisms through which TRPV1 channels couple coronary blood flow to metabolism are not fully understood. We employed mice lacking TRPV1 [TRPV1(−/−)], db/db diabetic, and control C57BKS/J mice to determine the extent to which TRPV1 channels modulate coronary function and contribute to vascular dysfunction in diabetic cardiomyopathy. Animals were subjected to in vivo infusion of the TRPV1 agonist capsaicin to examine the hemodynamic actions of TRPV1 activation. Capsaicin (1–100 μg·kg−1·min−1) dose dependently increased coronary blood flow in control mice, which was inhibited by the TRPV1 antagonist capsazepine or the nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (l-NAME). In addition, the capsaicin-mediated increase in blood flow was attenuated in db/db mice. TRPV1(−/−) mice exhibited no changes in coronary blood flow in response to capsaicin. Vasoreactivity studies in isolated pressurized mouse coronary microvessels revealed a capsaicin-dependent relaxation that was inhibited by the TRPV1 inhibitor SB366791 l-NAME and to the large conductance calcium-sensitive potassium channel (BK) inhibitors iberiotoxin and Penetrim A. Similar to in vivo responses, capsaicin-mediated relaxation was impaired in db/db mice compared with controls. Changes in pH (pH 7.4–6.0) relaxed coronary vessels contracted to the thromboxane mimetic U46619 in all three groups of mice; however, pH-mediated relaxation was blunted in vessels obtained from TRPV1(−/−) and db/db mice compared with controls. Western blot analysis revealed decreased myocardial TRPV1 protein expression in db/db mice compared with controls. Our data reveal TRPV1 channels mediate coupling of myocardial blood flow to cardiac metabolism via a nitric oxide-dependent, BK channel-dependent pathway that is corrupted in diabetes.

Urodynamic properties and neurotransmitter dependence of urinary bladder contractility in the BK channel deletion model of overactive bladder

2005 ◽  
Vol 289 (3) ◽  
pp. F604-F610 ◽  
Author(s):  
K. S. Thorneloe ◽  
A. L. Meredith ◽  
A. M. Knorn ◽  
R. W. Aldrich ◽  
M. T. Nelson
Keyword(s):  
Urinary Bladder ◽  
Overactive Bladder ◽  
Bk Channels ◽  
Bk Channel ◽  
Bladder Pressure ◽  
Bladder Smooth Muscle ◽  
Medical Issues ◽  
Urinary Bladder Smooth Muscle ◽  
Important Therapeutic Target

Overactive bladder and incontinence are major medical issues, which lack effective therapy. Previously, we showed (Meredith AL, Thornloe KS, Werner ME, Nelson MT, and Aldrich RW. J Biol Chem 279: 36746–36752, 2004) that the gene mSlo1 encodes large-conductance Ca2+-activated K+ (BK) channels of urinary bladder smooth muscle (UBSM) and that ablation of mSlo1 leads to enhanced myogenic and nerve-mediated contractility and increased urination frequency. Here, we examine the in vivo urodynamic consequences and neurotransmitter dependence in the absence of the BK channel. The sensitivity of contractility to nerve stimulation was greatly enhanced in UBSM strips from Slo−/− mice. The stimulation frequency required to obtain a 50% maximal contraction was 8.3 ± 0.9 and 19.1 ± 1.8 Hz in Slo−/− and Slo +/+ mice, respectively. This enhancement is at least partially due to alterations in UBSM excitability, as muscarinic-induced Slo−/− contractility is elevated in the absence of neuronal activity. Muscarinic-induced Slo−/− contractility was mimicked by blocking BK channels with iberiotoxin (IBTX) in Slo +/+ strips, whereas IBTX had no effect on Slo−/− strips. IBTX also enhanced purinergic contractions of Slo +/+ UBSM but was without effect on purinergic contractions of Slo−/− strips. In vivo bladder pressure and urine output measurements (cystometry) were performed on conscious, freely moving mice. Slo−/− mice exhibited increased bladder pressures, pronounced pressure oscillations, and urine dripping. Our results indicate that the BK channel in UBSM has a very significant role in urinary function and dysfunction and as such likely represents an important therapeutic target.

scholarly journals BK channels promote neuromuscular transmission

2020 ◽  
Vol 152 (5) ◽  
Author(s):  
Ben Short
Keyword(s):  
Neuromuscular Transmission ◽  
Neuromuscular Junctions ◽  
Bk Channels ◽  
Vesicle Release

Mice lacking BK channels are weak because of reduced vesicle release at neuromuscular junctions.

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 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.

scholarly journals Mechanism of Increased BK Channel Activation from a Channel Mutation that Causes Epilepsy

2009 ◽  
Vol 133 (3) ◽  
pp. 283-294 ◽  
Author(s):  
Bin Wang ◽  
Brad S. Rothberg ◽  
Robert Brenner
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Dissociation Constants ◽  
Bk Channels ◽  
Bk Channel ◽  
Gain Of Function ◽  
Gating Model ◽  
Voltage Dependent ◽  
Human Mutation ◽  
Opposing Effects

Concerted depolarization and Ca2+ rise during neuronal action potentials activate large-conductance Ca2+- and voltage-dependent K+ (BK) channels, whose robust K+ currents increase the rate of action potential repolarization. Gain-of-function BK channels in mouse knockout of the inhibitory β4 subunit and in a human mutation (αD434G) have been linked to epilepsy. Here, we investigate mechanisms underlying the gain-of-function effects of the equivalent mouse mutation (αD369G), its modulation by the β4 subunit, and potential consequences of the mutation on BK currents during action potentials. Kinetic analysis in the context of the Horrigan-Aldrich allosteric gating model revealed that changes in intrinsic and Ca2+-dependent gating largely account for the gain-of-function effects. D369G causes a greater than twofold increase in the closed-to-open equilibrium constant (6.6e−7→1.65e−6) and an approximate twofold decrease in Ca2+-dissociation constants (closed channel: 11.3→5.2 µM; open channel: 0.92→0.54 µM). The β4 subunit inhibits mutant channels through a slowing of activation kinetics. In physiological recording solutions, we established the Ca2+ dependence of current recruitment during action potential–shaped stimuli. D369G and β4 have opposing effects on BK current recruitment, where D369G reduces and β4 increases K1/2 (K1/2 μM: αWT 13.7, αD369G 6.3, αWT/β4 24.8, and αD369G/β4 15.0). Collectively, our results suggest that the D369G enhancement of intrinsic gating and Ca2+ binding underlies greater contributions of BK current in the sharpening of action potentials for both α and α/β4 channels.

β2 and β4 Subunits of BK Channels Confer Differential Sensitivity to Acute Modulation by Steroid Hormones

2006 ◽  
Vol 95 (5) ◽  
pp. 2878-2888 ◽  
Author(s):  
J. T. King ◽  
P. V. Lovell ◽  
M. Rishniw ◽  
M. I. Kotlikoff ◽  
M. L. Zeeman ◽  
...  
Keyword(s):  
Steroid Hormones ◽  
Bk Channels ◽  
Bk Channel ◽  
Differential Sensitivity ◽  
Adrenal Androgen ◽  
Hek 293 ◽  
293 Cells ◽  
Steroid Sensitivity ◽  
Dose Dependent

Membrane-associated receptors for rapid, steroidal neuromodulation remain elusive. Estradiol has been reported to facilitate activation of voltage- and Ca2+-dependent BK potassium channels encoded by Slo, if associated with β1 subunits. We show here that 1) multiple members of the β family confer sensitivity to multiple steroids on BK channels, 2) that β subunits differentiate between steroids, and 3) that different βs have distinct relative preferences for particular steroids. Expressed in HEK 293 cells, inside-out patches with channels composed of Slo-α alone showed no steroid sensitivity. Cells expressing αβ4 exhibited potent, rapid, reversible, and dose-dependent potentiation by corticosterone (CORT; a glucocorticoid), and were potentiated to a lesser degree by other sex and stress steroids. In contrast, αβ2 channels were potentiated more strongly by dehydroepiandrosterone (DHEA; an enigmatic, stress-related adrenal androgen), and to a lesser extent by CORT, estradiol, testosterone, and DHEA-S. Cholesterol had no effect on any BK channel compositions tested. Conductance–voltage plots of channels composed of α plus β2 or β4 subunits were shifted in the negative direction by steroids, indicating greater activation at negative voltages. Thus our results argue that the variety of Slo-β subunit coexpression patterns occurring in vivo expands the repertoire of Slo channel gating in yet another dimension not fully appreciated, rendering BK gating responsive to dynamic fluctuations in a multiple of steroid hormones.

scholarly journals Regulation of endothelial BK channels by heme oxygenase-derived carbon monoxide and caveolin-1

2012 ◽  
Vol 303 (1) ◽  
pp. C92-C101 ◽  
Author(s):  
Melissa A. Riddle ◽  
Benjimen R. Walker
Keyword(s):  
Carbon Monoxide ◽  
Heme Oxygenase ◽  
Barometric Pressure ◽  
Inhibitory Effect ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activity ◽  
Outward Currents ◽  
In Cells

A novel vasodilatory influence of endothelial cell (EC) large-conductance Ca2+-activated K+ (BK) channels is present after in vivo exposure to chronic hypoxia (CH) and may exist in other pathological states. However, the mechanism of channel activation that results in altered vasoreactivity is unknown. Previously, we demonstrated that inhibition of either BK channels or heme oxygenase (HO) restores vasoconstrictor reactivity after CH. Additionally, administration of the scaffolding domain of caveolin (Cav)-1 inhibits EC BK activity and restores vasoconstrictor reactivity in this setting. These results led us to hypothesize that CH exposure results in a loss in Cav-1 inhibition of EC BK channels, resulting in their activation by HO-derived carbon monoxide (CO). Experiments were conducted on freshly dispersed aortic ECs from control and CH-exposed (barometric pressure: 380 mmHg for 48 h) rats. In electrophysiology experiments, outward currents were greater in cells from CH rats as well as from cells from control rats treated with the cholesterol-depleting agent methyl-β-cyclodextrin. These enhanced currents were returned to control by HO inhibition. Channel activity could be restored by the CO donor CO-releasing molecule (CORM)-2 during HO inhibition. Administration of the Cav-1 scaffolding domain eliminated BK currents in cells from CH rats, and current was not restored by the addition of CORM-2. Colocalization experiments in ECs from control and CH rats demonstrated an association between HO-2, Cav-1, and BK. We conclude that EC BK channel activity is HO dependent in the absence of the inhibitory effect of the Cav-1 scaffolding domain.

Characteristics of Ca2+ release for activation of K+ current and contractile system in some smooth muscles

1996 ◽  
Vol 271 (3) ◽  
pp. C772-C782 ◽  
Author(s):  
Y. Imaizumi ◽  
S. Henmi ◽  
Y. Uyama ◽  
K. Atsuki ◽  
Y. Torii ◽  
...  
Keyword(s):  
Single Cells ◽  
Smooth Muscles ◽  
Bk Channels ◽  
Bk Channel ◽  
Channel Activity ◽  
Acetoxymethyl Ester ◽  
Contractile System ◽  
Outward Currents ◽  
K Current ◽  
Spontaneous Transient Outward Currents

Characteristics of Ca2+ release from stores were investigated in strips from ileum and portal vein and in isolated myocytes from ileum and urinary bladder of the guinea pig with use of caffeine and 9-methyl-7-bromoeudistomin D (MBED), a potent releaser of Ca2+ from skeletal muscle sarcoplasmic reticulum. In skinned strips, 1-30 mM caffeine elicited a transient contraction, but 10-300 microM MBED did not. Pretreatment with 100 microM MBED did not affect the subsequent caffeine-induced contraction. In single cells loaded with indo 1-acetoxymethyl ester, 10 mM caffeine increased cytoplasmic Ca2+ concentration, whereas 100 microM MBED elicited a small or no increase. Under whole cell clamp, spontaneous transient outward currents through Ca(2+)-dependent K+ (BK) channels were first enhanced and then suppressed by 30 microM MBED or 5 mM caffeine. The amplitude of Ca(2+)-dependent transient K+ current on depolarization was reduced by MBED and caffeine (50% inhibitory concentrations = 20 microM and 1 mM, respectively). Other currents and single BK channel activity were not significantly affected by MBED. The Ca2+ release from stores responsible for BK channel activation may be resolved from that for the activation of the contractile system by MBED in these smooth muscle cells.

scholarly journals BK channel activation by NS11021 decreases excitability and contractility of urinary bladder smooth muscle

2010 ◽  
Vol 298 (2) ◽  
pp. R378-R384 ◽  
Author(s):  
Jeffrey J. Layne ◽  
Bernhard Nausch ◽  
Søren-Peter Olesen ◽  
Mark T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Urinary Bladder ◽  
Action Potentials ◽  
Bk Channels ◽  
Bk Channel ◽  
Bladder Smooth Muscle ◽  
Open Probability ◽  
Urinary Bladder Smooth Muscle ◽  
Spontaneous Action ◽  
Spontaneous Action Potentials

Large-conductance Ca2+-activated potassium (BK) channels play an important role in regulating the function and activity of urinary bladder smooth muscle (UBSM), and the loss of BK channel function has been shown to increase UBSM excitability and contractility. However, it is not known whether activation of BK channels has the converse effect of reducing UBSM excitability and contractility. Here, we have sought to investigate this possibility by using the novel BK channel opener NS11021. NS11021 (3 μM) caused an approximately threefold increase in both single BK channel open probability ( Po) and whole cell BK channel currents. The frequency of spontaneous action potentials in UBSM strips was reduced by NS11021 from a control value of 20.9 ± 5.9 to 10.9 ± 3.7 per minute. NS11021 also reduced the force of UBSM spontaneous phasic contractions by ∼50%, and this force reduction was blocked by pretreatment with the BK channel blocker iberiotoxin. NS11021 (3 μM) had no effect on contractions evoked by nerve stimulation. These findings indicate that activating BK channels reduces the force of UBSM spontaneous phasic contractions, principally through decreasing the frequency of spontaneous action potentials.

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