scholarly journals Theoretical Study of the Function of the IP3 Receptor / BK Channel Complex in a Single Neuron

2021 ◽  
Author(s):  
◽  
M. E. Pérez-Bonilla
Keyword(s):  
Plasma Membrane ◽  
Calcium Influx ◽  
Ryanodine Receptors ◽  
Cytosolic Calcium ◽  
Bk Channels ◽  
Bk Channel ◽  
Ip3 Receptors ◽  
Ip3 Receptor ◽  
Calcium Efflux ◽  
The Central Nervous System

Large conductance calcium-activated potassium (BK) channels carry out many functions in the central nervous system. The opening of BK channels requires a rise in the cytosolic calcium ([Ca2+]cyt) concentration, which can occur in two ways: calcium influx from voltage-gated calcium channels (VGCCs) located on the plasma membrane and calcium efflux through the endoplasmic reticulum (ER) membrane to the cytosol triggered by inositol 1,4,5-trisphosphate (IP3) receptors (IP3-Rs) and ryanodine receptors (RyRs). The BK channel/IP3-R/RyR interaction has been widely reported in smooth muscle but scarce information exist on neurons, where its presence is uncertain. The aim of this study was to develop a computational model of a neuron to replicate the interaction between the release of Ca2+ from the ER (through IP3-Rs and RyRs) and the opening of BK channels on the plasma membrane to regulate the level of [Ca2+]cyt, based on the Hodgkin-Huxley formalism and the Goldbeter model. The mathematical models were implemented on Visual Basic® and differential equations were solved numerically. Various conditions of BK conductance and the efflux of endoplasmic Ca2+ were explored. The results show that an abrupt increase in [Ca2+]cyt (≥ 5 mM) activates the BK channels and either pauses or stops the action potential train.

scholarly journals ERG-28 controls BK channel trafficking in the ER to regulate synaptic function and alcohol response in C. elegans

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Kelly H Oh ◽  
James J Haney ◽  
Xiaohong Wang ◽  
Chiou-Fen Chuang ◽  
Janet E Richmond ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Neurotransmitter Release ◽  
Calcium Influx ◽  
Bk Channels ◽  
Bk Channel ◽  
Synaptic Function ◽  
Neural Function ◽  
Channel Trafficking ◽  
C Elegans ◽  
Calcium Dependent

Voltage- and calcium-dependent BK channels regulate calcium-dependent cellular events such as neurotransmitter release by limiting calcium influx. Their plasma membrane abundance is an important factor in determining BK current and thus regulation of calcium-dependent events. In C. elegans, we show that ERG-28, an endoplasmic reticulum (ER) membrane protein, promotes the trafficking of SLO-1 BK channels from the ER to the plasma membrane by shielding them from premature degradation. In the absence of ERG-28, SLO-1 channels undergo aspartic protease DDI-1-dependent degradation, resulting in markedly reduced expression at presynaptic terminals. Loss of erg-28 suppressed phenotypic defects of slo-1 gain-of-function mutants in locomotion, neurotransmitter release, and calcium-mediated asymmetric differentiation of the AWC olfactory neuron pair, and conferred significant ethanol-resistant locomotory behavior, resembling slo-1 loss-of-function mutants, albeit to a lesser extent. Our study thus indicates that the control of BK channel trafficking is a critical regulatory mechanism for synaptic transmission and neural function.

scholarly journals Nanoscale coupling of junctophilin-2 and ryanodine receptors regulates vascular smooth muscle cell contractility

2019 ◽  
Vol 116 (43) ◽  
pp. 21874-21881 ◽  
Author(s):  
Harry A. T. Pritchard ◽  
Caoimhin S. Griffin ◽  
Evan Yamasaki ◽  
Pratish Thakore ◽  
Conor Lane ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Plasma Membrane ◽  
Cerebral Arteries ◽  
Ryanodine Receptors ◽  
Bk Channels ◽  
Bk Channel ◽  
Functional Coupling ◽  
Superresolution Microscopy ◽  
Cell Contractility ◽  
Channel Currents

Junctophilin proteins maintain close contacts between the endoplasmic/sarcoplasmic reticulum (ER/SR) and the plasma membrane in many types of cells, as typified by junctophilin-2 (JPH2), which is necessary for the formation of the cardiac dyad. Here, we report that JPH2 is the most abundant junctophilin isotype in native smooth muscle cells (SMCs) isolated from cerebral arteries and that acute knockdown diminishes the area of sites of interaction between the SR and plasma membrane. Superresolution microscopy revealed nanometer-scale colocalization of JPH2 clusters with type 2 ryanodine receptor (RyR2) clusters near the cell surface. Knockdown of JPH2 had no effect on the frequency, amplitude, or kinetics of spontaneous Ca2+ sparks generated by transient release of Ca2+ from the SR through RyR2s, but it did nearly abolish Ca2+ spark-activated, large-conductance, Ca2+-activated K+ (BK) channel currents. We also found that JPH2 knockdown was associated with hypercontractility of intact cerebral arteries. We conclude that JPH2 maintains functional coupling between RyR2s and BK channels and is critically important for cerebral arterial function.

The Yin and Yang of BK Channels in Epilepsy

2018 ◽  
Vol 17 (4) ◽  
pp. 272-279 ◽  
Author(s):  
Yudan Zhu ◽  
Shuzhang Zhang ◽  
Yijun Feng ◽  
Qian Xiao ◽  
Jiwei Cheng ◽  
...  
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Bk Channels ◽  
Bk Channel ◽  
Potential Shape ◽  
Yin And Yang ◽  
The Central Nervous System ◽  
Action Potential Shape ◽  
Excitability Of Neurons

Background & Objective: The large conductance calcium-activated potassium (BK) channel, extensively distributed in the central nervous system (CNS), is considered as a vital player in the pathogenesis of epilepsy, with evidence implicating derangement of K+ as well as regulating action potential shape and duration. However, unlike other channels implicated in epilepsy whose function in neurons could clearly be labeled “excitatory” or “inhibitory”, the unique physiological behavior of the BK channel allows it to both augment and decrease the excitability of neurons. Thus, the role of BK in epilepsy is controversial so far, and a growing area of intense investigation. Conclusion: Here, this review aims to highlight recent discoveries on the dichotomous role of BK channels in epilepsy, focusing on relevant BK-dependent pro- as well as antiepileptic pathways, and discuss the potential of BK specific modulators for the treatment of epilepsy.

Association of the hepatic IP3 receptor with the plasma membrane: relevance to mode of action

1993 ◽  
Vol 265 (6) ◽  
pp. C1588-C1596 ◽  
Author(s):  
L. Feng ◽  
N. Kraus-Friedmann
Keyword(s):  
Plasma Membrane ◽  
Membrane Fraction ◽  
Ip3 Receptors ◽  
Ip3 Receptor ◽  
Plasma Membrane Fraction ◽  
T Lymphoma Cells ◽  
T Lymphoma ◽  
Triton X ◽  
Brain Receptor ◽  
The Brain

Studies were carried out to characterize the interaction between inositol 1,4,5-trisphosphate (IP3) receptors and the plasma membrane fraction. Extraction of the membranes with the nonionic detergents Nonidet P-40 and Triton X-100, followed by centrifugation at 100,000 g, resulted in the doubling of the IP3 receptor in the pellets, whereas no detectable binding was found in the supernatants. These data indicate that the detergents did not solubilize the receptor, that it remained associated with membrane particles, and that it is likely to be associated with the cytoskeleton. The cytoskeleton proteins actin, ankyrin, and spectrin were identified in the plasma membrane fraction. However, comparison of the amount of these proteins in different fractions of the detergent, or otherwise treated plasma membrane fractions, showed no direct correlation between the presence of any of these proteins in the plasma membrane fraction and their ability to bind [3H]IP3. This is in contrast to the brain and T-lymphoma cells in which the IP3 receptor is attached to ankyrin (L. Y. W. Bourguigon, H. Jin, N. Iida, N. R. Brandt, and S. H. Zhang. J. Biol. Chem. 268: 6477-6486, 1993; and S. K. Joseph and S. Samanta. J. Biol. Chem 268: 6477-6486, 1993). Thus the hepatic IP3 receptor, which is different from the brain receptor, might attach to the cytoskeleton by anchoring to a different protein. Because cytochalasin D treatment of livers diminishes the ability of IP3 to raise cytosolic free Ca2+ levels, the attachment of the IP3 receptor to the cytoskeleton seems to involve an association with microfilaments.

scholarly journals Econazole inhibits thapsigargin-induced platelet calcium influx by mechanisms other than cytochrome P-450 inhibition

1993 ◽  
Vol 295 (2) ◽  
pp. 525-529 ◽  
Author(s):  
J G Vostal ◽  
J C Fratantoni
Keyword(s):  
Plasma Membrane ◽  
Antifungal Agents ◽  
Calcium Influx ◽  
Calcium Stores ◽  
Alternative Mechanism ◽  
Resting Cells ◽  
Calcium Efflux ◽  
Plasma Membrane Permeability ◽  
Cytochrome P 450 ◽  
Internal Calcium

Cytochrome P-450 has been suggested as a mediator of the signal between depleted platelet calcium stores and an increase in plasma membrane permeability to calcium which follows depletion of the stores. This hypothesis is based on the observations that inhibitors of cytochrome P-450, such as the imidazole antifungal agents, also inhibit influx of a calcium surrogate (manganese) into calcium-depleted platelets. We tested the effects of econazole and of a cytochrome P-450 inhibitor, carbon monoxide (CO), on thapsigargin (TG)-induced platelet 45Ca2+ influx. TG specifically depletes internal calcium stores and activates store-regulated calcium influx. Econazole blocked 45Ca2+ influx when it was added before TG (IC50 11 microM). Econazole at a concentration (20 microM) that inhibited 83% of TG-induced calcium influx was not inhibitory to TG-induced calcium efflux from 45Ca(2+)-loaded platelets, and did not affect calcium fluxes in resting platelets. This econazole concentration was also inhibitory to calcium influx even when it was added after the stores had been calcium-depleted by EGTA and TG for 15 min and the signal to increase calcium influx had already been generated. Inhibition of cytochrome P-450 with CO bubbled through platelet suspensions did not change calcium influx in resting cells and potentiated TG-induced calcium influx (160% of control calcium accumulation at 20 min). This effect appeared to be concentration-dependent, such that a 5 min exposure to CO produced a greater influx potentiation than a 3 min exposure. These observations indicate that (1) cytochrome P-450 does not mediate store-regulated calcium influx, and (2) econazole probably inhibits store-regulated calcium influx by an alternative mechanism, such as interaction with plasma membrane calcium channels.

scholarly journals Large-conductance calcium-activated potassium current modulates excitability in isolated canine intracardiac neurons

2013 ◽  
Vol 304 (3) ◽  
pp. C280-C286 ◽  
Author(s):  
Guillermo J. Pérez ◽  
Mayurika Desai ◽  
Seth Anderson ◽  
Fabiana S. Scornik
Keyword(s):  
Membrane Potential ◽  
Calcium Release ◽  
Single Channel ◽  
Calcium Influx ◽  
Ryanodine Receptors ◽  
Bk Channels ◽  
Release Mechanism ◽  
Dependent Manner ◽  
Whole Cell ◽  
Intracardiac Neurons

We studied principal neurons from canine intracardiac (IC) ganglia to determine whether large-conductance calcium-activated potassium (BK) channels play a role in their excitability. We performed whole cell recordings in voltage- and current-clamp modes to measure ion currents and changes in membrane potential from isolated canine IC neurons. Whole cell currents from these neurons showed fast- and slow-activated outward components. Both current components decreased in the absence of calcium and following 1–2 mM tetraethylammonium (TEA) or paxilline. These results suggest that BK channels underlie these current components. Single-channel analysis showed that BK channels from IC neurons do not inactivate in a time-dependent manner, suggesting that the dynamic of the decay of the fast current component is akin to that of intracellular calcium. Immunohistochemical studies showed that BK channels and type 2 ryanodine receptors are coexpressed in IC principal neurons. We tested whether BK current activation in these neurons occurred via a calcium-induced calcium release mechanism. We found that the outward currents of these neurons were not affected by the calcium depletion of intracellular stores with 10 mM caffeine and 10 μM cyclopiazonic acid. Thus, in canine intracardiac neurons, BK currents are directly activated by calcium influx. Membrane potential changes elicited by long (400 ms) current injections showed a tonic firing response that was decreased by TEA or paxilline. These data strongly suggest that the BK current present in canine intracardiac neurons regulates action potential activity and could increase these neurons excitability.

scholarly journals Oligodendrocytes, BK channels and the preservation of myelin

F1000Research ◽  
2021 ◽  
Vol 10 ◽  
pp. 781
Author(s):  
Maddalena Rupnik ◽  
David Baker ◽  
David L. Selwood
Keyword(s):  
Demyelinating Disease ◽  
Bk Channels ◽  
Bk Channel ◽  
Neurological Disability ◽  
Excitatory Neurotransmitter ◽  
Neuronal Excitation ◽  
Current Therapies ◽  
The Central Nervous System ◽  
Immunomodulatory Therapies

Oligodendrocytes wrap multiple lamellae of their membrane, myelin, around axons of the central nervous system (CNS), to improve impulse conduction. Myelin synthesis is specialised and dynamic, responsive to local neuronal excitation. Subtle pathological insults are sufficient to cause significant neuronal metabolic impairment, so myelin preservation is necessary to safeguard neural networks. Multiple sclerosis (MS) is the most prevalent demyelinating disease of the CNS. In MS, inflammatory attacks against myelin, proposed to be autoimmune, cause myelin decay and oligodendrocyte loss, leaving neurons vulnerable. Current therapies target the prominent neuroinflammation but are mostly ineffective in protecting from neurodegeneration and the progressive neurological disability. People with MS have substantially higher levels of extracellular glutamate, the main excitatory neurotransmitter. This impairs cellular homeostasis to cause excitotoxic stress. Large conductance Ca2+-activated K+ channels (BK channels) could preserve myelin or allow its recovery by protecting cells from the resulting excessive excitability. This review evaluates the role of excitotoxic stress, myelination and BK channels in MS pathology, and explores the hypothesis that BK channel activation could be a therapeutic strategy to protect oligodendrocytes from excitotoxic stress in MS. This could reduce progression of neurological disability if used in parallel to immunomodulatory therapies.

scholarly journals BK in Double-Membrane Organelles: A Biophysical, Pharmacological, and Functional Survey

2021 ◽  
Vol 12 ◽  
Author(s):  
Naileth González-Sanabria ◽  
Felipe Echeverría ◽  
Ignacio Segura ◽  
Rosangelina Alvarado-Sánchez ◽  
Ramon Latorre
Keyword(s):  
Skeletal Muscle ◽  
Plasma Membrane ◽  
Potassium Channel ◽  
Lipid Bilayers ◽  
Bk Channels ◽  
Bk Channel ◽  
Inner Mitochondrial Membrane ◽  
Modular Architecture ◽  
Open Probability ◽  
Α Subunit

In the 1970s, calcium-activated potassium currents were recorded for the first time. In 10years, this Ca2+-activated potassium channel was identified in rat skeletal muscle, chromaffin cells and characterized in skeletal muscle membranes reconstituted in lipid bilayers. This calcium- and voltage-activated potassium channel, dubbed BK for “Big K” due to its large ionic conductance between 130 and 300 pS in symmetric K+. The BK channel is a tetramer where the pore-forming α subunit contains seven transmembrane segments. It has a modular architecture containing a pore domain with a highly potassium-selective filter, a voltage-sensor domain and two intracellular Ca2+ binding sites in the C-terminus. BK is found in the plasma membrane of different cell types, the inner mitochondrial membrane (mitoBK) and the nuclear envelope’s outer membrane (nBK). Like BK channels in the plasma membrane (pmBK), the open probability of mitoBK and nBK channels are regulated by Ca2+ and voltage and modulated by auxiliary subunits. BK channels share common pharmacology to toxins such as iberiotoxin, charybdotoxin, paxilline, and agonists of the benzimidazole family. However, the precise role of mitoBK and nBK remains largely unknown. To date, mitoBK has been reported to play a role in protecting the heart from ischemic injury. At the same time, pharmacology suggests that nBK has a role in regulating nuclear Ca2+, membrane potential and expression of eNOS. Here, we will discuss at the biophysical level the properties and differences of mitoBK and nBK compared to those of pmBK and their pharmacology and function.

scholarly journals Opposing roles of smooth muscle BK channels and ryanodine receptors in the regulation of nerve-evoked constriction of mesenteric resistance arteries

2014 ◽  
Vol 306 (7) ◽  
pp. H981-H988 ◽  
Author(s):  
Gayathri Krishnamoorthy ◽  
Swapnil K. Sonkusare ◽  
Thomas J. Heppner ◽  
Mark T. Nelson
Keyword(s):  
Smooth Muscle ◽  
Cerebral Arteries ◽  
Ryanodine Receptors ◽  
Electrical Field Stimulation ◽  
Bk Channels ◽  
Bk Channel ◽  
Mesenteric Arteries ◽  
Resistance Arteries ◽  
Sympathetic Nerve Activation ◽  
Neurogenic Vasoconstriction

In depolarized smooth muscle cells of pressurized cerebral arteries, ryanodine receptors (RyRs) generate “Ca2+ sparks” that activate large-conductance, Ca2+-, and voltage-sensitive potassium (BK) channels to oppose pressure-induced (myogenic) constriction. Here, we show that BK channels and RyRs have opposing roles in the regulation of arterial tone in response to sympathetic nerve activation by electrical field stimulation. Inhibition of BK channels with paxilline increased both myogenic and nerve-induced constrictions of pressurized, resistance-sized mesenteric arteries from mice. Inhibition of RyRs with ryanodine increased myogenic constriction, but it decreased nerve-evoked constriction along with a reduction in the amplitude of nerve-evoked increases in global intracellular Ca2+. In the presence of L-type voltage-dependent Ca2+ channel (VDCC) antagonists, nerve stimulation failed to evoke a change in arterial diameter, and BK channel and RyR inhibitors were without effect, suggesting that nerve- induced constriction is dependent on activation of VDCCs. Collectively, these results indicate that BK channels and RyRs have different roles in the regulation of myogenic versus neurogenic tone: whereas BK channels and RyRs act in concert to oppose myogenic vasoconstriction, BK channels oppose neurogenic vasoconstriction and RyRs augment it. A scheme for neurogenic vasoregulation is proposed in which RyRs act in conjunction with VDCCs to regulate nerve-evoked constriction in mesenteric resistance arteries.

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