BK channel beta4 subunit reduces dentate gyrus excitability and protects against temporal lobe seizures

Transmembrane determinants of voltage-gating differences between BK (Slo1) and Slo3 channels

Voltage-gated potassium channels are critical in modulating cellular excitability, with Slo (slowpoke) channels forming a unique family characterized by their large conductance and dual regulation by electrical signals and intracellular messengers. Despite their structural and evolutionary similarities, Slo1 and Slo3 channels exhibit significant differences in their voltage-gating properties. This study investigates the molecular determinants that differentiate the voltage-gating properties of human Slo1 and mouse Slo3 channels. Utilizing Slo1/Slo3 chimeras, we pinpointed the selectivity filter region as a key factor in the Slo3 channel's reduced conductance at negative voltages. The S6 transmembrane (TM) segment was identified as pivotal for the Slo3 channel's biphasic deactivation kinetics at these voltages. Additionally, the S4 and S6 TM segments were found to be responsible for the gradual slope in the Slo3 channel's conductance-voltage relationship, while multiple TM regions appear to be involved in the Slo3 channel's requirement of strong depolarization for activation. Mutations in the Slo1's S5 and S6 TM segments revealed three residues (I233, L302, and M304) that likely play a crucial role in the allosteric coupling between the voltage sensors and the pore gate.

Attenuating midline thalamus bursting to mitigate absence epilepsy

Advancing the mechanistic understanding of absence epilepsy is crucial for developing new therapeutics, especially for patients unresponsive to current treatments. Utilizing a recently developed mouse model of absence epilepsy carrying the BK gain-of-function channelopathy D434G, here we report that attenuating the burst firing of midline thalamus (MLT) neurons effectively prevents absence seizures. We found that enhanced BK channel activity in the BK-D434G MLT neurons promotes synchronized bursting during the ictal phase of absence seizures. Modulating MLT neurons through pharmacological reagents, optogenetic stimulation, or deep brain stimulation effectively attenuates burst firing, leading to reduced absence seizure frequency and increased vigilance. Additionally, enhancing vigilance by amphetamine, a stimulant medication, or physical perturbation also effectively suppresses MLT bursting and prevents absence seizures. These findings suggest that the MLT is a promising target for clinical interventions. Our diverse approaches offer valuable insights for developing next generation therapeutics to treat absence epilepsy.

Challenges in the Therapeutic Targeting of KCa Channels: From Basic Physiology to Clinical Applications

Calcium-activated potassium (KCa) channels are ubiquitously expressed throughout the body and are able to regulate membrane potential and intracellular calcium concentrations, thereby playing key roles in cellular physiology and signal transmission. Consequently, it is unsurprising that KCa channels have been implicated in various diseases, making them potential targets for pharmaceutical interventions. Over the past two decades, numerous studies have been conducted to develop KCa channel-targeting drugs, including those for disorders of the central and peripheral nervous, cardiovascular, and urinary systems and for cancer. In this review, we synthesize recent findings regarding the structure and activating mechanisms of KCa channels. We also discuss the role of KCa channel modulators in therapeutic medicine. Finally, we identify the major reasons behind the delay in bringing these modulators to the pharmaceutical market and propose new strategies to promote their application.

BK Channelopathies and KCNMA1-Linked Disease Models

Novel KCNMA1 variants, encoding the BK K+ channel, are associated with a debilitating dyskinesia and epilepsy syndrome. Neurodevelopmental delay, cognitive disability, and brain and structural malformations are also diagnosed at lower incidence. More than half of affected individuals present with a rare negative episodic motor disorder, paroxysmal nonkinesigenic dyskinesia (PNKD3). The mechanistic relationship of PNKD3 to epilepsy and the broader spectrum of KCNMA1-associated symptomology is unknown. This review summarizes patient-associated KCNMA1 variants within the BK channel structure, functional classifications, genotype-phenotype associations, disease models, and treatment. Patient and transgenic animal data suggest delineation of gain-of-function (GOF) and loss-of-function KCNMA1 neurogenetic disease, validating two heterozygous alleles encoding GOF BK channels (D434G and N999S) as causing seizure and PNKD3. This discovery led to a variant-defined therapeutic approach for PNKD3, providing initial insight into the neurological basis. A comprehensive clinical definition of monogenic KCNMA1-linked disease and the neuronal mechanisms currently remain priorities for continued investigation.

TAT-Modified Martentoxin Displays Intravenous Antiseizure Activities

Epilepsy is a chronic disease of brain dysfunction, which arises from imbalance between excitatory and inhibitory activities in neural circuits. Previously, we reported that peptide Martentoxin (MarTX), from scorpion Buthus martensii Karsch, displayed antiseizure activities by specifically inhibiting BK(α + β4) channel currents. Injection of MarTX into the hippocampal region of mice significantly alleviated convulsive seizures. However, intravenous injection of MarTX had no antiepileptic efficacy due to the blood-brain barrier (BBB). To address this, here, we designed cell-penetrating peptide TAT-modified MarTX, in which the linker containing three glycines was put between TAT and the N-terminus of MarTX (forming MTX-N-TAT) or between TAT and the C-terminus of MarTX (forming MTX-C-TAT), respectively. We prepared them in a large amount through Escherichia coli overexpression system and then probed their antiseizure activities. Our results indicated that intravenous injection of MTX-C-TAT showed significant therapeutic efficacy of antiseizure. It increased seizure latency, reduced the total seizure duration and the number of seizures at stages 3, 4, and 5, inhibited hippocampal neuronal hyperexcitability, and exhibited neuroprotective effects on hippocampal neurons. These studies implied that MTX-C-TAT displayed intravenous antiseizure activities properly through crossing BBB and would be a potential antiepileptic drug in the future.

Peroxisome proliferator-activated receptor-α activation facilitates contextual fear extinction and modulates intrinsic excitability of dentate gyrus neurons

The dentate gyrus (DG) of the hippocampus encodes contextual information associated with fear, and cell activity in the DG is required for acquisition and extinction of contextual fear. However, the underlying molecular mechanisms are not fully understood. Here we show that mice deficient for peroxisome proliferator-activated receptor-α (PPARα) exhibited a slower rate of contextual fear extinction. Furthermore, selective deletion of PPARα in the DG attenuated, while activation of PPARα in the DG by local infusion of aspirin facilitated extinction of contextual fear. The intrinsic excitability of DG granule neurons was reduced by PPARα deficiency but increased by activation of PPARα with aspirin. Using RNA-Seq transcriptome we found that the transcription level of neuropeptide S receptor 1 (Npsr1) was tightly correlated with PPARα activation. Our results provide evidence that PPARα plays an important role in regulating DG neuronal excitability and contextual fear extinction.

Targeting Ion Channels and Purkinje Neuron Intrinsic Membrane Excitability as a Therapeutic Strategy for Cerebellar Ataxia

In degenerative neurological disorders such as Parkinson's disease, a convergence of widely varying insults results in a loss of dopaminergic neurons and, thus, the motor symptoms of the disease. Dopamine replacement therapy with agents such as levodopa is a mainstay of therapy. Cerebellar ataxias, a heterogeneous group of currently untreatable conditions, have not been identified to have a shared physiology that is a target of therapy. In this review, we propose that perturbations in cerebellar Purkinje neuron intrinsic membrane excitability, a result of ion channel dysregulation, is a common pathophysiologic mechanism that drives motor impairment and vulnerability to degeneration in cerebellar ataxias of widely differing genetic etiologies. We further propose that treatments aimed at restoring Purkinje neuron intrinsic membrane excitability have the potential to be a shared therapy in cerebellar ataxia akin to levodopa for Parkinson's disease.

BK channel modulation by positively charged peptides and auxiliary γ subunits mediated by the Ca2+-bowl site

The large-conductance, Ca2+-, and voltage-activated K+ (BK) channel consists of the pore-forming α (BKα) subunit and regulatory β and γ subunits. The γ1-3 subunits facilitate BK channel activation by shifting the voltage-dependence of channel activation toward the hyperpolarization direction by about 50-150 mV in the absence of Ca2+. We previously found that the intracellular C-terminal positively charged regions of the γ subunits play important roles in BK channel modulation. In this study, we found that the intracellular C-terminal region of BKα is indispensable in BK channel modulation by the γ1 subunit. Notably, synthetic peptide mimics of the γ1-3 subunits' C-terminal positively charged regions caused 30-50 mV shifts in BKα channel voltage-gating toward the hyperpolarization direction. The cationic cell-penetrating HIV-1 Tat peptide exerted a similar BK channel-activating effect. The BK channel-activating effects of the synthetic peptides were reduced in the presence of Ca2+ and markedly ablated by both charge neutralization of the Ca2+-bowl site and high ionic strength, suggesting the involvement of electrostatic interactions. The efficacy of the γ subunits in BK channel modulation was reduced by charge neutralization of the Ca2+-bowl site. However, BK channel modulation by the γ1 subunit was little affected by high ionic strength and the positively charged peptide remained effective in BK channel modulation in the presence of the γ1 subunit. These findings identify positively charged peptides as BK channel modulators and reveal a role for the Ca2+-bowl site in BK channel modulation by positively charged peptides and the C-terminal positively charged regions of auxiliary γ subunits.

Deubiquitinase CYLD regulates excitatory synaptic transmission and short-term plasticity in the hippocampus

The fate of proteins is determined by the addition of various forms of polyubiquitin during ubiquitin-mediated proteasomal degradation. Cylindromatosis (CYLD), a K63-specific deubiquitinase, is enriched in postsynaptic density fractions of the rodent central nervous system (CNS), but the synaptic role of CYLD in the CNS is poorly understand. Here we show that CYLD deficiency (Cyld^-/-) results in reduced intrinsic hippocampal neuronal firing, a decrease in the frequency of spontaneous excitatory postsynaptic currents and a decrease in the amplitude of field excitatory postsynaptic potentials. Moreover, Cyld^-/- hippocampus shows downregulated levels of presynaptic vesicular glutamate transporter 1 (vGlut1) and upregulated levels of postsynaptic GluA1, a subunit of the AMPA receptor, together with an altered paired-pulse ratio (PPR). We also found increased activation of astrocytes and microglia in the hippocampus of Cyld^-/- mice. The present study suggests a critical role for CYLD in mediating hippocampal neuronal and synaptic activity.

Ethanol Metabolite, Acetate, Increases Excitability of the Central Nucleus of Amygdala Neurons through Activation of NMDA Receptors

The central nucleus of the amygdala (CeA) is a key brain region involved in emotional and stressor responses due to its many projections to autonomic regulatory centers. It is also a primary site of action from ethanol consumption. However, the influence of active metabolites of ethanol such as acetate on the CeA neural circuitry has yet to be elucidated. Here, we investigated the effect of acetate on CeA neurons with the axon projecting to the rostral ventrolateral medulla (CeA-RVLM), as well as quantified cytosolic calcium responses in primary neuronal cultures. Whole-cell patch-clamp recordings in brain slices containing autonomic CeA-RVLM neurons revealed a dose-dependent increase in neuronal excitability in response to acetate. N-Methyl-d-aspartate receptor (NMDAR) antagonists suppressed the acetate-induced increase in CeA-RVLM neuronal excitability and memantine suppressed the direct activation of NMDAR-dependent inward currents by acetate in brain slices. We observed that acetate increased cytosolic Ca2+ in a time-dependent manner in primary neuronal cell cultures. The acetate enhancement of calcium signaling was abolished by memantine. Computational modeling of acetic acid at NMDAR/NR1 glutamatergic and glycinergic sites suggests potential active site interactions. These findings suggest that within the CeA, acetate is excitatory at least partially through activation of NMDAR, which may underlie the impact of ethanol consumption on autonomic circuitry.

Modulation of neuronal excitability by binge alcohol drinking

Drug use poses a serious threat to health systems throughout the world. The number of consumers rises every year being alcohol the drug of abuse most consumed causing 3 million deaths (5.3% of all deaths) worldwide and 132.6 million disability-adjusted life years. In this review, we present an up-to-date summary about what is known regarding the global impact of binge alcohol drinking on brains and how it affects the development of cognitive functions, as well as the various preclinical models used to probe its effects on the neurobiology of the brain. This will be followed by a detailed report on the state of our current knowledge of the molecular and cellular mechanisms underlying the effects of binge drinking on neuronal excitability and synaptic plasticity, with an emphasis on brain regions of the meso-cortico limbic neurocircuitry.

Ca2+- and Voltage-Activated K+ (BK) Channels in the Nervous System: One Gene, a Myriad of Physiological Functions

BK channels are large conductance potassium channels characterized by four pore-forming α subunits, often co-assembled with auxiliary β and γ subunits to regulate Ca2+ sensitivity, voltage dependence and gating properties. BK channels are abundantly expressed throughout the brain and in different compartments within a single neuron, including axons, synaptic terminals, dendritic arbors, and spines. Their activation produces a massive efflux of K+ ions that hyperpolarizes the cellular membrane. Together with their ability to detect changes in intracellular Ca2+ concentration, BK channels control neuronal excitability and synaptic communication through diverse mechanisms. Moreover, increasing evidence indicates that dysfunction of BK channel-mediated effects on neuronal excitability and synaptic function has been implicated in several neurological disorders, including epilepsy, fragile X syndrome, mental retardation, and autism, as well as in motor and cognitive behavior. Here, we discuss current evidence highlighting the physiological importance of this ubiquitous channel in regulating brain function and its role in the pathophysiology of different neurological disorders.

KCa-Related Neurological Disorders: Phenotypic Spectrum and Therapeutic Indications

Although potassium channelopathies have been linked to a wide range of neurological conditions, the underlying pathogenic mechanism is not always clear, and a systematic summary of clinical manifestation is absent. Several neurological disorders have been associated with alterations of calcium-activated potassium channels (KCa channels), such as loss- or gain-of-function mutations, post-transcriptional modification, etc. Here, we outlined the current understanding of the molecular and cellular properties of three subtypes of KCa channels, including big conductance KCa channels (BK), small conductance KCa channels (SK), and the intermediate conductance KCa channels (IK). Next, we comprehensively reviewed the loss- or gain-of-function mutations of each KCa channel and described the corresponding mutation sites in specific diseases to broaden the phenotypic-genotypic spectrum of KCa-related neurological disorders. Moreover, we reviewed the current pharmaceutical strategies targeting KCa channels in KCa-related neurological disorders to provide new directions for drug discovery in anti-seizure medication.

Development of charybdotoxin Q18F variant as a selective peptide blocker of neuronal BK(α + β4) channel for the treatment of epileptic seizures

Epilepsy is the results from the imbalance between inhibition and excitation in neural circuits, which is mainly treated by some chemical drugs with side effects. Gain-of-function of BK channels or knockout of its β4 subunit associates with spontaneous epilepsy. Currently, few reports were published about the efficacy of BK(α + β4) channel modulators in epilepsy prevention. Charybdotoxin is a non-specific inhibitor of BK and other K+ channels. Here, by nuclear magnetic resonance (NMR) and other biochemical techniques, we found that charybdotoxin might interact with the extracellular loop of human β4 subunit (i.e., hβ4-loop) of BK(α + β4) channel at a molar ratio 4:1 (hβ4-loop vs. charybdotoxin). Charybdotoxin enhanced its ability to prevent K+ current of BK(α + β4 H101Y) channel. The charybdotoxin Q18F variant selectively reduced the neuronal spiking frequency and increased interspike intervals of BK(α + β4) channel by π-π stacking interactions between its residue Phe18 and residue His101 of hβ4-loop. Moreover, intrahippocampal infusion of charybdotoxin Q18F variant significantly increased latency time of seizure, reduced seizure duration and seizure numbers on pentylenetetrazole-induced pre-sensitized rats, inhibited hippocampal hyperexcitability and c-Fos expression, and displayed neuroprotective effects on hippocampal neurons. These results implied that charybdotoxin Q18F variant could be potentially used for intractable epilepsy treatment by therapeutically targeting BK(α + β4) channel.

Further Studies on the Role of BTBD9 in the Cerebellum, Sleep-like Behaviors and the Restless Legs Syndrome

Genetic analyses have linked BTBD9 to restless legs syndrome (RLS) and sleep regulation. Btbd9 knockout mice show RLS-like motor restlessness. Previously, we found hyperactivity of cerebellar Purkinje cells (PCs) in Btbd9 knockout mice, which may contribute to the motor restlessness observed. However, underlying mechanisms for PC hyperactivity in Btbd9 knockout mice are unknown. Here, we used dissociated PC recording, brain slice recording and western blot to address this question. Our dissociated recording shows that knockout PCs had increased TEA-sensitive, Ca2+-dependent K+ currents. Applying antagonist to large conductance Ca2+-activated K+ (BK) channels further isolated the increased current as BK current. Consistently, we found increased amplitude of afterhyperpolarization and elevated BK protein levels in the knockout mice. Dissociated recording also shows a decrease in TEA-insensitive, Ca2+-dependent K+ currents. The result is consistent with reduced amplitude of tail currents, mainly composed of small conductance Ca2+-activated K+ (SK) currents, in slice recording. Our results suggest that BK and SK channels may be responsible for the hyperactivity of knockout PCs. Recently, BTBD9 protein was shown to associate with SYNGAP1 protein. We found a decreased cerebellar level of SYNGAP1 in Btbd9 knockout mice. However, Syngap1 heterozygous knockout mice showed nocturnal, instead of diurnal, motor restlessness. Our results suggest that SYNGAP1 deficiency may not contribute directly to the RLS-like motor restlessness observed in Btbd9 knockout mice. Finally, we found that PC-specific Btbd9 knockout mice exhibited deficits in motor coordination and balance similar to Btbd9 knockout mice, suggesting that the motor effect of BTBD9 in PCs is cell-autonomous.

Neuronal splicing regulator RBFOX3 mediates seizures via regulating Vamp1 expression preferentially in NPY-expressing GABAergic neurons

Epilepsy is a common neurological disorder, which has been linked to mutations or deletions of RNA binding protein, fox-1 homolog (Caenorhabditis elegans) 3 (RBFOX3)/NeuN, a neuronal splicing regulator. However, the mechanism of seizure mediation by RBFOX3 remains unknown. Here, we show that mice with deletion of Rbfox3 in gamma-aminobutyric acid (GABA) ergic neurons exhibit spontaneous seizures and high premature mortality due to increased presynaptic release, postsynaptic potential, neuronal excitability, and synaptic transmission in hippocampal dentate gyrus granule cells (DGGCs). Attenuating early excitatory gamma-aminobutyric acid (GABA) action by administering bumetanide, an inhibitor of early GABA depolarization, rescued premature mortality. Rbfox3 deletion reduced hippocampal expression of vesicle-associated membrane protein 1 (VAMP1), a GABAergic neuron-specific presynaptic protein. Postnatal restoration of VAMP1 rescued premature mortality and neuronal excitability in DGGCs. Furthermore, Rbfox3 deletion in GABAergic neurons showed fewer neuropeptide Y (NPY)-expressing GABAergic neurons. In addition, deletion of Rbfox3 in NPY-expressing GABAergic neurons lowered intrinsic excitability and increased seizure susceptibility. Our results establish RBFOX3 as a critical regulator and possible treatment path for epilepsy.

BK channel properties correlate with neurobehavioral severity in three KCNMA1-linked channelopathy mouse models

KCNMA1 forms the pore of BK K+ channels, which regulate neuronal and muscle excitability. Recently, genetic screening identified heterozygous KCNMA1 variants in a subset of patients with debilitating paroxysmal non-kinesigenic dyskinesia, presenting with or without epilepsy (PNKD3). However, the relevance of KCNMA1 mutations and the basis for clinical heterogeneity in PNKD3 has not been established. Here, we evaluate the relative severity of three KCNMA1 patient variants in BK channels, neurons, and mice. In heterologous cells, BKN999S and BKD434G channels displayed gain-of-function (GOF) properties, whereas BKH444Q channels showed loss-of-function (LOF) properties. The relative degree of channel activity was BKN999S > BKD434G>WT > BKH444Q. BK currents and action potential firing were increased, and seizure thresholds decreased, in Kcnma1N999S/WT and Kcnma1D434G/WT transgenic mice but not Kcnma1H444Q/WT mice. In a novel behavioral test for paroxysmal dyskinesia, the more severely affected Kcnma1N999S/WT mice became immobile after stress. This was abrogated by acute dextroamphetamine treatment, consistent with PNKD3-affected individuals. Homozygous Kcnma1D434G/D434G mice showed similar immobility, but in contrast, homozygous Kcnma1H444Q/H444Q mice displayed hyperkinetic behavior. These data establish the relative pathogenic potential of patient alleles as N999S>D434G>H444Q and validate Kcnma1N999S/WT mice as a model for PNKD3 with increased seizure propensity.

Neuronal mechanism of a BK channelopathy in absence epilepsy and dyskinesia

BK channelopathy has been increasingly implicated in diverse neurological disorders, including epilepsy and movement, cognitive, and neurodevelopmental disorders. However, precision medicine to treat BK channelopathy is lacking. We characterized a mouse model carrying a gain-of-function BK channelopathy D434G from a large family of patients with absence epilepsy and paroxysmal dyskinesia. The BK-D434G mice manifest the clinical features of absence seizures and exhibit severe locomotor defects including involuntary dyskinesia-like behavior. Pharmacological inhibition of BK channels suppresses neuronal hyperactivity and mitigates absence seizure and the locomotor defects. The BK-D434G mice thus serve as a model to understand the pathogenic mechanisms of absence epilepsy and dyskinesia. Our study also suggests that BK inhibition is a promising strategy for treating BK gain-of-function channelopathy.

A growing number of gain-of-function (GOF) BK channelopathies have been identified in patients with epilepsy and movement disorders. Nevertheless, the underlying pathophysiology and corresponding therapeutics remain obscure. Here, we utilized a knock-in mouse model carrying human BK-D434G channelopathy to investigate the neuronal mechanism of BK GOF in the pathogenesis of epilepsy and dyskinesia. The BK-D434G mice manifest the clinical features of absence epilepsy and exhibit severe motor deficits and dyskinesia-like behaviors. The cortical pyramidal neurons and cerebellar Purkinje cells from the BK-D434G mice show hyperexcitability, which likely contributes to the pathogenesis of absence seizures and paroxysmal dyskinesia. A BK channel blocker, paxilline, potently suppresses BK-D434G–induced hyperexcitability and effectively mitigates absence seizures and locomotor deficits in mice. Our study thus uncovered a neuronal mechanism of BK GOF in absence epilepsy and dyskinesia. Our findings also suggest that BK inhibition is a promising therapeutic strategy for mitigating BK GOF-induced neurological disorders.

Molecular Mechanisms of Epileptic Encephalopathy Caused by KCNMA1 Loss-of-Function Mutations

The gene kcnma1 encodes the α-subunit of high-conductance calcium- and voltage-dependent K⁺ (BK) potassium channel. With the development of generation gene sequencing technology, many KCNMA1 mutants have been identified and are more closely related to generalized epilepsy and paroxysmal dyskinesia. Here, we performed a genetic screen of 26 patients with febrile seizures and identified a novel mutation of KCNMA1 (E155Q). Electrophysiological characterization of different KCNMA1 mutants in HEK 293T cells, the previously-reported R458T and E884K variants (not yet determined), as well as the newly-found E155Q variant, revealed that the current density amplitude of all the above variants was significantly smaller than that of the wild-type (WT) channel. All the above variants caused a positive shift of the I-V curve and played a role through the loss-of-function (LOF) mechanism. Moreover, the β4 subunit slowed down the activation of the E155Q mutant. Then, we used kcnma1 knockout (BK KO) mice as the overall animal model of LOF mutants. It was found that BK KO mice had spontaneous epilepsy, motor impairment, autophagic dysfunction, abnormal electroencephalogram (EEG) signals, as well as possible anxiety and cognitive impairment. In addition, we performed transcriptomic analysis on the hippocampus and cortex of BK KO and WT mice. We identified many differentially expressed genes (DEGs). Eight dysregulated genes [i.e., (Gfap and Grm3 associated with astrocyte activation) (Alpl and Nlrp10 associated with neuroinflammation) (Efna5 and Reln associated with epilepsy) (Cdkn1a and Nr4a1 associated with autophagy)] were validated by RT-PCR, which showed a high concordance with transcriptomic analysis. Calcium imaging results suggested that BK might regulate the autophagy pathway from TRPML1. In conclusion, our study indicated that newly-found point E155Q resulted in a novel loss-of-function variant and the dysregulation of gene expression, especially astrocyte activation, neuroinflammation and autophagy, might be the molecular mechanism of BK-LOF meditated epilepsy.

Structural and Functional Coupling of Calcium-Activated BK Channels and Calcium-Permeable Channels Within Nanodomain Signaling Complexes

Biochemical and functional studies of ion channels have shown that many of these integral membrane proteins form macromolecular signaling complexes by physically associating with many other proteins. These macromolecular signaling complexes ensure specificity and proper rates of signal transduction. The large-conductance, Ca²⁺-activated K⁺ (BK) channel is dually activated by membrane depolarization and increases in intracellular free Ca²⁺ ([Ca²⁺]_i). The activation of BK channels results in a large K⁺ efflux and, consequently, rapid membrane repolarization and closing of the voltage-dependent Ca²⁺-permeable channels to limit further increases in [Ca²⁺]_i. Therefore, BK channel-mediated K⁺ signaling is a negative feedback regulator of both membrane potential and [Ca²⁺]_i and plays important roles in many physiological processes and diseases. However, the BK channel formed by the pore-forming and voltage- and Ca²⁺-sensing α subunit alone requires high [Ca²⁺]_i levels for channel activation under physiological voltage conditions. Thus, most native BK channels are believed to co-localize with Ca²⁺-permeable channels within nanodomains (a few tens of nanometers in distance) to detect high levels of [Ca²⁺]_i around the open pores of Ca²⁺-permeable channels. Over the last two decades, advancement in research on the BK channel’s coupling with Ca²⁺-permeable channels including recent reports involving NMDA receptors demonstrate exemplary models of nanodomain structural and functional coupling among ion channels for efficient signal transduction and negative feedback regulation. We hereby review our current understanding regarding the structural and functional coupling of BK channels with different Ca²⁺-permeable channels.

A familiar study on self-limited childhood epilepsy patients using hIPSC-derived neurons shows a bias towards immaturity at the morphological, electrophysiological and gene expression levels

Background

Self-limited Childhood Epilepsies are the most prevalent epileptic syndrome in children. Its pathogenesis is unknown. In this disease, symptoms resolve spontaneously in approximately 50% of patients when maturity is reached, prompting to a maturation problem. The purpose of this study was to understand the molecular bases of this disease by generating and analyzing induced pluripotent stem cell-derived neurons from a family with 7 siblings, among whom 4 suffer from this disease.

Methods

Two affected siblings and, as controls, a healthy sister and the unaffected mother of the family were studied. Using exome sequencing, a homozygous variant in the FYVE, RhoGEF and PH Domain Containing 6 gene was identified in the patients as a putative genetic factor that could contribute to the development of this familial disorder. After informed consent was signed, skin biopsies from the 4 individuals were collected, fibroblasts were derived and reprogrammed and neurons were generated and characterized by markers and electrophysiology. Morphological, electrophysiological and gene expression analyses were performed on these neurons.

Results

Bona fide induced pluripotent stem cells and derived neurons could be generated in all cases. Overall, there were no major shifts in neuronal marker expression among patient and control-derived neurons. Compared to two familial controls, neurons from patients showed shorter axonal length, a dramatic reduction in synapsin-1 levels and cytoskeleton disorganization. In addition, neurons from patients developed a lower action potential threshold with time of in vitro differentiation and the amount of current needed to elicit an action potential (rheobase) was smaller in cells recorded from NE derived from patients at 12 weeks of differentiation when compared with shorter times in culture. These results indicate an increased excitability in patient cells that emerges with the time in culture. Finally, functional genomic analysis showed a biased towards immaturity in patient-derived neurons.

Conclusions

We are reporting the first in vitro model of self-limited childhood epilepsy, providing the cellular bases for future in-depth studies to understand its pathogenesis. Our results show patient-specific neuronal features reflecting immaturity, in resonance with the course of the disease and previous imaging studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02658-2.

The Large-Conductance, Calcium-Activated Potassium Channel: A Big Key Regulator of Cell Physiology

Large-conductance Ca²⁺-activated K⁺ channels facilitate the efflux of K⁺ ions from a variety of cells and tissues following channel activation. It is now recognized that BK channels undergo a wide range of pre- and post-translational modifications that can dramatically alter their properties and function. This has downstream consequences in affecting cell and tissue excitability, and therefore, function. While finding the “silver bullet” in terms of clinical therapy has remained elusive, ongoing research is providing an impressive range of viable candidate proteins and mechanisms that associate with and modulate BK channel activity, respectively. Here, we provide the hallmarks of BK channel structure and function generally, and discuss important milestones in the efforts to further elucidate the diverse properties of BK channels in its many forms.

Differential regulation of BK channels by fragile X mental retardation protein

Fragile X mental retardation protein (FMRP) is an RNA-binding protein prominently expressed in neurons. Missense mutations or complete loss of FMRP can potentially lead to fragile X syndrome, a common form of inherited intellectual disability. In addition to RNA regulation, FMRP was also proposed to modulate neuronal function by direct interaction with the large conductance Ca²⁺- and voltage-activated potassium channel (BK) β₄ regulatory subunits (BKβ₄). However, the molecular mechanisms underlying FMRP regulation of BK channels were not studied in detail. We have used electrophysiology and super-resolution stochastic optical reconstruction microscopy (STORM) to characterize the effects of FMRP on pore-forming BKα subunits, as well as the association with regulatory subunits BKβ₄. Our data indicate that, in the absence of coexpressed β₄, FMRP alters the steady-state properties of BKα channels by decreasing channel activation and deactivation rates. Analysis using the Horrigan-Aldrich model revealed alterations in the parameters associated with channel opening (L₀) and voltage sensor activation (J₀). Interestingly, FMRP also altered the biophysical properties of BKαβ₄ channels favoring channel opening, although not as dramatically as BKα. STORM experiments revealed clustered multi-protein complexes, consistent with FMRP interacting not only to BKαβ₄ but also to BKα. Lastly, we found that a partial loss-of-function mutation in FMRP (R138Q) counteracts many of its functional effects on BKα and BKαβ₄ channels. In summary, our data show that FMRP modulates the function of both BKα and BKαβ₄ channels.

Roles of Key Ion Channels and Transport Proteins in Age-Related Hearing Loss

The auditory system is a fascinating sensory organ that overall, converts sound signals to electrical signals of the nervous system. Initially, sound energy is converted to mechanical energy via amplification processes in the middle ear, followed by transduction of mechanical movements of the oval window into electrochemical signals in the cochlear hair cells, and finally, neural signals travel to the central auditory system, via the auditory division of the 8th cranial nerve. The majority of people above 60 years have some form of age-related hearing loss, also known as presbycusis. However, the biological mechanisms of presbycusis are complex and not yet fully delineated. In the present article, we highlight ion channels and transport proteins, which are integral for the proper functioning of the auditory system, facilitating the diffusion of various ions across auditory structures for signal transduction and processing. Like most other physiological systems, hearing abilities decline with age, hence, it is imperative to fully understand inner ear aging changes, so ion channel functions should be further investigated in the aging cochlea. In this review article, we discuss key various ion channels in the auditory system and how their functions change with age. Understanding the roles of ion channels in auditory processing could enhance the development of potential biotherapies for age-related hearing loss.

Potassium channels as prominent targets and tools for the treatment of epilepsy

INTRODUCTION

K⁺ channels are of great interest to epilepsy research as mutations in their genes are found in humans with inherited epilepsy. At the level of cellular physiology, K+ channels control neuronal intrinsic excitability and are the main contributors to membrane repolarization of active neurons. Recently, a genetically modified voltage-dependent K⁺ channel has been patented as a remedy for epileptic seizures.

AREAS COVERED

We review the role of potassium channels in excitability, clinical and experimental evidence for the association of potassium channelopathies with epilepsy, the targeting of K+ channels by drugs, and perspectives of gene therapy in epilepsy with the expression of extra K+ channels in the brain.

EXPERT OPINION

Control over K+ conductance is of great potential benefit for the treatment of epilepsy. Nowadays, gene therapy affecting K+ channels is one of the most promising approaches to treat pharmacoresistant focal epilepsy.

Impaired plasticity of intrinsic excitability in the dentate gyrus alters spike transfer in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by cognitive decline related to deficits in synaptic transmission and plasticity. We report in APP/PS1 mice, a double transgenic mouse model of AD, that females displayed an early burden of Aβ plaques load in the stratum moleculare of the dentate gyrus (DG) together with prominent neuroinflammatory activation of astrocytes and microglia. Robust deficits in hippocampus-dependent memory tasks were observed in APP/PS1 female mice as early as 3 months of age. We then studied the functional properties of the lateral perforant path (LPP) to DG granule cells. Remarkably DG granule cells displayed higher intrinsic excitability in APP/PS1 female mice. We showed that the long term potentiation of population spike amplitude induced by high frequency stimulation (HFS) at LPP-DG granule cells synapse is impaired in APP/PS1 female mice. HFS induced plasticity of intrinsic excitability in DG granule cells without inducing noticeable modification of synaptic strength. Furthermore, the enhanced intrinsic excitability was potentiated to a greater extent in APP/PS1 as compared to control mice following HFS. Our study shows that changes in the intrinsic excitability of DG granule cells in AD contribute to the dysfunctional transfer of information from the entorhinal cortex to the hippocampus.

Ion-channel regulation of response decorrelation in a heterogeneous multi-scale model of the dentate gyrus

Heterogeneities in biological neural circuits manifest in afferent connectivity as well as in local-circuit components such as neuronal excitability, neural structure and local synaptic strengths. The expression of adult neurogenesis in the dentate gyrus (DG) amplifies local-circuit heterogeneities and guides heterogeneities in afferent connectivity. How do neurons and their networks endowed with these distinct forms of heterogeneities respond to perturbations to individual ion channels, which are known to change under several physiological and pathophysiological conditions? We sequentially traversed the ion channels-neurons-network scales and assessed the impact of eliminating individual ion channels on conductance-based neuronal and network models endowed with disparate local-circuit and afferent heterogeneities. We found that many ion channels differentially contributed to specific neuronal or network measurements, and the elimination of any given ion channel altered several functional measurements. We then quantified the impact of ion-channel elimination on response decorrelation, a well-established metric to assess the ability of neurons in a network to convey complementary information, in DG networks endowed with different forms of heterogeneities. Notably, we found that networks constructed with structurally immature neurons exhibited functional robustness, manifesting as minimal changes in response decorrelation in the face of ion-channel elimination. Importantly, the average change in output correlation was dependent on the eliminated ion channel but invariant to input correlation. Our analyses suggest that neurogenesis-driven structural heterogeneities could assist the DG network in providing functional resilience to molecular perturbations.

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Perturbations at one scale result in a cascading impact on physiology across scales.

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Heterogeneous multi-scale models used to assess the impact of ion-channel deletion.

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Mapping of structural components to functional outcomes is many-to-many.

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Differential & variable impact of ion channel deletion on response decorrelation.

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Neurogenesis-induced structural heterogeneity confers resilience to perturbations.

BK Channel Regulation of Afterpotentials and Burst Firing in Cerebellar Purkinje Neurons

BK calcium-activated potassium channels have complex kinetics because they are activated by both voltage and cytoplasmic calcium. The timing of BK activation and deactivation during action potentials determines their functional role in regulating firing patterns but is difficult to predict a priori. We used action potential clamp to characterize the kinetics of voltage-dependent calcium current and BK current during action potentials in Purkinje neurons from mice of both sexes, using acutely dissociated neurons that enabled rapid voltage clamp at 37°C. With both depolarizing voltage steps and action potential waveforms, BK current was entirely dependent on calcium entry through voltage-dependent calcium channels. With voltage steps, BK current greatly outweighed the triggering calcium current, with only a brief, small net inward calcium current before Ca-activated BK current dominated the total Ca-dependent current. During action potential waveforms, although BK current activated with only a short (∼100 μs) delay after calcium current, the two currents were largely separated, with calcium current flowing during the falling phase of the action potential and most BK current flowing over several milliseconds after repolarization. Step depolarizations activated both an iberiotoxin-sensitive BK component with rapid activation and deactivation kinetics and a slower-gating iberiotoxin-resistant component. During action potential firing, however, almost all BK current came from the faster-gating iberiotoxin-sensitive channels, even during bursts of action potentials. Inhibiting BK current had little effect on action potential width or a fast afterhyperpolarization but converted a medium afterhyperpolarization to an afterdepolarization and could convert tonic firing of single action potentials to burst firing.SIGNIFICANCE STATEMENT BK calcium-activated potassium channels are widely expressed in central neurons. Altered function of BK channels is associated with epilepsy and other neuronal disorders, including cerebellar ataxia. The functional role of BK in regulating neuronal firing patterns is highly dependent on the context of other channels and varies widely among different types of neurons. Most commonly, BK channels are activated during action potentials and help produce a fast afterhyperpolarization. We find that in Purkinje neurons BK current flows primarily after the fast afterhyperpolarization and helps to prevent a later afterdepolarization from producing rapid burst firing, enabling typical regular tonic firing.

The distinct roles of calcium in rapid control of neuronal glycolysis and the tricarboxylic acid cycle

When neurons engage in intense periods of activity, the consequent increase in energy demand can be met by the coordinated activation of glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. However, the trigger for glycolytic activation is unknown and the role for Ca2+ in the mitochondrial responses has been debated. Using genetically encoded fluorescent biosensors and NAD(P)H autofluorescence imaging in acute hippocampal slices, here we find that Ca2+ uptake into the mitochondria is responsible for the buildup of mitochondrial NADH, probably through Ca2+ activation of dehydrogenases in the TCA cycle. In the cytosol, we do not observe a role for the Ca2+/calmodulin signaling pathway, or AMPK, in mediating the rise in glycolytic NADH in response to acute stimulation. Aerobic glycolysis in neurons is triggered mainly by the energy demand resulting from either Na+ or Ca2+ extrusion, and in mouse dentate granule cells, Ca2+ creates the majority of this demand.

Functionally distinct POMC-expressing neuron subpopulations in hypothalamus revealed by intersectional targeting

Pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus represent key regulators of metabolic homeostasis. Electrophysiological and single-cell sequencing experiments have revealed a remarkable degree of heterogeneity of these neurons. However, the exact molecular basis and functional consequences of this heterogeneity have not yet been addressed. Here, we have developed new mouse models in which intersectional Cre/Dre-dependent recombination allowed for successful labeling, translational profiling and functional characterization of distinct POMC neurons expressing the leptin receptor (Lepr) and glucagon like peptide 1 receptor (Glp1r). Our experiments reveal that POMC^Lepr+ and POMC^Glp1r+ neurons represent largely nonoverlapping subpopulations with distinct basic electrophysiological properties. They exhibit a specific anatomical distribution within the arcuate nucleus and differentially express receptors for energy-state communicating hormones and neurotransmitters. Finally, we identify a differential ability of these subpopulations to suppress feeding. Collectively, we reveal a notably distinct functional microarchitecture of critical metabolism-regulatory neurons.

Chronic ethanol exposure differentially alters neuronal function in the medial prefrontal cortex and dentate gyrus

Alterations in the function of prefrontal cortex (PFC) and hippocampus have been implicated in underlying the relapse to alcohol seeking behaviors in humans and animal models of moderate to severe alcohol use disorders (AUD). Here we used chronic intermittent ethanol vapor exposure (CIE), 21d protracted abstinence following CIE (21d AB), and re-exposure to one vapor session during protracted abstinence (re-exposure) to evaluate the effects of chronic ethanol exposure on basal synaptic function, neuronal excitability and expression of key synaptic proteins that play a role in neuronal excitability in the medial PFC (mPFC) and dentate gyrus (DG). CIE consistently enhanced excitability of layer 2/3 pyramidal neurons in the mPFC and granule cell neurons in the DG. In the DG, this effect persisted during 21d AB. Re-exposure did not enhance excitability, suggesting resistance to vapor-induced effects. Analysis of action potential kinetics revealed that altered afterhyperpolarization, rise time and decay time constants are associated with the altered excitability during CIE, 21d AB and re-exposure. Molecular adaptations that may underlie increases in neuronal excitability under these different conditions were identified. Quantitative polymerase chain reaction of large-conductance potassium (BK) channel subunit mRNA in PFC and DG tissue homogenates did not show altered expression patterns of BK subunits. Western blotting demonstrates enhanced phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), and reduced phosphorylation of glutamate receptor GluN2A/2B subunits. These results suggest a novel relationship between activity of CaMKII and GluN receptors in the mPFC and DG, and neuronal excitability in these brain regions in the context of moderate to severe AUD.

Astrocytes as Guardians of Neuronal Excitability: Mechanisms Underlying Epileptogenesis

Astrocytes are key homeostatic regulators in the central nervous system and play important roles in physiology. After brain damage caused by e.g., status epilepticus, traumatic brain injury, or stroke, astrocytes may adopt a reactive phenotype. This process of reactive astrogliosis is important to restore brain homeostasis. However, persistent reactive astrogliosis can be detrimental for the brain and contributes to the development of epilepsy. In this review, we will focus on physiological functions of astrocytes in the normal brain as well as pathophysiological functions in the epileptogenic brain, with a focus on acquired epilepsy. We will discuss the role of astrocyte-related processes in epileptogenesis, including reactive astrogliosis, disturbances in energy supply and metabolism, gliotransmission, and extracellular ion concentrations, as well as blood-brain barrier dysfunction and dysregulation of blood flow. Since dysfunction of astrocytes can contribute to epilepsy, we will also discuss their role as potential targets for new therapeutic strategies.

BK potassium currents contribute differently to action potential waveform and firing rate as rat hippocampal neurons mature in the first postnatal week

This work describes the early developmental trends of large-conductance calcium-activated potassium (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.

Modulation of TRPV4 and BKCa for treatment of brain diseases

As a member of transient receptor potential family, the transient receptor potential vanilloid 4 (TRPV4) is a kind of nonselective calcium-permeable cation channel, which belongs to non-voltage gated Ca²⁺ channel. Large-conductance Ca²⁺-activated K⁺ channel (BKCa) represents a unique superfamily of Ca²⁺-activated K⁺ channel (KCa) that is both voltage and intracellular Ca²⁺ dependent. Not surprisingly, aberrant function of either TRPV4 or BKCa in neurons has been associated with brain disorders, such as Alzheimer's disease, cerebral ischemia, brain tumor, epilepsy, as well as headache. In these diseases, vascular dysfunction is a common characteristic. Notably, endothelial and smooth muscle TRPV4 can mediate BKCa to regulate cerebral blood flow and pressure. Therefore, in this review, we not only discuss the diverse functions of TRPV4 and BKCa in neurons to integrate relative signaling pathways in the context of cerebral physiological and pathological situations respectively, but also reveal the relationship between TRPV4 and BKCa in regulation of cerebral vascular tone as an etiologic factor. Based on these analyses, this review demonstrates the effective mechanisms of compounds targeting these two channels, which may be potential therapeutic strategies for diseases in the brain.

Calcium-induced calcium release in proximity to hair cell BK channels revealed by PKA activation

Large-conductance calcium-activated potassium (BK) channels play a critical role in electrical resonance, a mechanism of frequency selectivity in chicken hair cells. We determine that BK currents are dependent on inward flow of Ca2+ , and intracellular buffering of Ca2+ . Entry of Ca2+ is further amplified locally by calcium-induced Ca2+ release (CICR) in close proximity to plasma membrane BK channels. Ca2+ imaging reveals peripheral clusters of high concentrations of Ca2+ that are suprathreshold to that needed to activate BK channels. Protein kinase A (PKA) activation increases the size of BK currents likely by recruiting more BK channels due to spatial spread of high Ca2+ concentrations in turn from increasing CICR. STORM imaging confirms the presence of nanodomains with ryanodine and IP3 receptors in close proximity to the Slo subunit of BK channels. Together, these data require a rethinking of how electrical resonance is brought about and suggest effects of CICR in synaptic release. Both genders were included in this study.

Prevention of brain damage after traumatic brain injury by pharmacological enhancement of KCNQ (Kv7, "M-type") K+ currents in neurons

Nearly three million people in the USA suffer traumatic brain injury (TBI) yearly; however, there are no pre- or post-TBI treatment options available. KCNQ2-5 voltage-gated K⁺ channels underlie the neuronal "M current", which plays a dominant role in the regulation of neuronal excitability. Our strategy towards prevention of TBI-induced brain damage is predicated on the suggested hyper-excitability of neurons induced by TBIs, and the decrease in neuronal excitation upon pharmacological augmentation of M/KCNQ K⁺ currents. Seizures are very common after a TBI, making further seizures and development of epilepsy disease more likely. Our hypothesis is that TBI-induced hyperexcitability and ischemia/hypoxia lead to metabolic stress, cell death and a maladaptive inflammatory response that causes further downstream morbidity. Using the mouse controlled closed-cortical impact blunt TBI model, we found that systemic administration of the prototype M-channel "opener", retigabine (RTG), 30 min after TBI, reduces the post-TBI cascade of events, including spontaneous seizures, enhanced susceptibility to chemo-convulsants, metabolic stress, inflammatory responses, blood-brain barrier breakdown, and cell death. This work suggests that acutely reducing neuronal excitability and energy demand via M-current enhancement may be a novel model of therapeutic intervention against post-TBI brain damage and dysfunction.

Regulation of BK Channels by Beta and Gamma Subunits

Ca²⁺- and voltage-gated K⁺ channels of large conductance (BK channels) are expressed in a diverse variety of both excitable and inexcitable cells, with functional properties presumably uniquely calibrated for the cells in which they are found. Although some diversity in BK channel function, localization, and regulation apparently arises from cell-specific alternative splice variants of the single pore-forming α subunit ( KCa1.1, Kcnma1, Slo1) gene, two families of regulatory subunits, β and γ, define BK channels that span a diverse range of functional properties. We are just beginning to unravel the cell-specific, physiological roles served by BK channels of different subunit composition.

Low-frequency Stimulation Decreases Hyperexcitability Through Adenosine A1 Receptors in the Hippocampus of Kindled Rats

INTRODUCTION

In this study, the role of A1 adenosine receptors in improving the effect of Low-Frequency Electrical Stimulation (LFS) on seizure-induced hyperexcitability of hippocampal CA1 pyramidal neurons was investigated.

METHODS

A semi-rapid hippocampal kindling model was used to induce seizures in male Wistar rats. Examination of the electrophysiological properties of CA1 pyramidal neurons of the hippocampus using whole-cell patch-clamp recording 48 h after the last kindling stimulation revealed that the application of LFS as two packages of stimulations at a time interval of 6 h for two consecutive days could significantly restore the excitability CA1 pyramidal neurons evidenced by a decreased in the of the number of evoked action potentials and enhancement of amplitude, maximum rise slope and decay slope of the first evoked action potential, rheobase, utilization time, adaptation index, first-spike latency, and post-AHP amplitude. Selective locked of A1 receptors by the administration of 8-Cyclopentyl-1,3-dimethylxanthine (1 μM, 1 μl, i.c.v.) before applying each LFS package, significantly reduced LFS effectiveness in recovering these parameters.

RESULTS

On the other hand, selective activation of A1 receptors by an injection of N6-cyclohexyladenosine (10 μM, 1 μl, i.c.v.), instead of LFS application, could imitate LFS function in improving these parameters.

CONCLUSION

It is suggested that LFS exerts its efficacy on reducing the neuronal excitability, partially by activating the adenosine system and activating its A1 receptors.

GABAergic Input Affects Intracellular Calcium Levels in Developing Granule Cells of Adult Rat Hippocampus

In the dentate gyrus (DG) of the mammalian hippocampus, granule neurons are generated from neural stem cells (NSCs) throughout the life span and are integrated into the hippocampal network. Adult DG neurogenesis is regulated by multiple intrinsic and extrinsic factors that control NSC proliferation, maintenance, and differentiation into mature neurons. γ-Aminobutyric acid (GABA), released by local interneurons, regulates the development of neurons born in adulthood by activating extrasynaptic and synaptic GABA_A receptors. In the present work, patch-clamp and calcium imaging techniques were used to record very immature granule cells of adult rat dentate gyrus for investigating the actual role of GABA_A receptor activation in intracellular calcium level regulation at an early stage of maturation. Our findings highlight a novel molecular and electrophysiological mechanism, involving calcium-activated potassium channels (BK) and T-type voltage-dependent calcium channels, through which GABA fine-tunes intracellular calcium homeostasis in rat adult-born granule neurons early during their maturation. This mechanism might be instrumental in promoting newborn cell survival.

Upregulation of Beta4 subunit of BKCa channels in the anterior cingulate cortex contributes to mechanical allodynia associated anxiety-like behaviors

The anterior cingulate cortex (ACC) serves as a critical hub for the anxiety and pain perception. The large-conductance Ca²⁺-activated potassium channels, or BK_Ca channels, are ubiquitously expressed throughout the central nervous system including the cingulate cortex. However, what changes of cortical BK_Ca channels undergo in the ACC remains unknown in pain-related anxiety. In the present study, a significant upregulation of synaptic and non-synaptic BK_Ca channel accessory β4 subunits in the ACC was accompanied with pain-associated anxiety-like behaviors in the chronic compression of multiple dorsal root ganglia (mCCD) of the rat. NS1619, an opener of BK_Ca channels, significantly rescued the alteration of fAHP and AP duration of ACC pyramidal neurons in mCCD rats. The mRNA expression of BK_Ca β4 subunits was extremely upregulated in the ACC after mCCD with the increased amount of both synaptic and non-synaptic BK_Ca β4 subunit protein. Meanwhile, NS1619 reversed the enhanced AMPA receptor-mediated spontaneous excitatory postsynaptic current (sEPSC) frequency and the attenuated PPR of ACC neurons in mCCD rats. Local activation of BK_Ca channels in the ACC reversed mechanical allodynia and anxiety-like behaviors. These results suggest that the upregulation of postsynaptic and presynaptic BK_Ca β4 subunit may contribute to neuronal hyperexcitability and the enhanced synaptic transmission in the ACC in neuropathic pain state, and then may result in anxiety-like behavior induced by neuropathic pain.

Molecular structures of the human Slo1 K+ channel in complex with β4

Slo1 is a Ca²⁺- and voltage-activated K⁺ channel that underlies skeletal and smooth muscle contraction, audition, hormone secretion and neurotransmitter release. In mammals, Slo1 is regulated by auxiliary proteins that confer tissue-specific gating and pharmacological properties. This study presents cryo-EM structures of Slo1 in complex with the auxiliary protein, β4. Four β4, each containing two transmembrane helices, encircle Slo1, contacting it through helical interactions inside the membrane. On the extracellular side, β4 forms a tetrameric crown over the pore. Structures with high and low Ca²⁺ concentrations show that identical gating conformations occur in the absence and presence of β4, implying that β4 serves to modulate the relative stabilities of 'pre-existing' conformations rather than creating new ones. The effects of β4 on scorpion toxin inhibition kinetics are explained by the crown, which constrains access but does not prevent binding.

A Mouse Model of Repetitive Blast Traumatic Brain Injury Reveals Post-Trauma Seizures and Increased Neuronal Excitability

Repetitive blast traumatic brain injury (TBI) affects numerous soldiers on the battlefield. Mild TBI has been shown to have long-lasting effects with repeated injury. We have investigated effects on neuronal excitability after repetitive, mild TBI in a mouse model of blast-induced brain injury. We exposed mice to mild blast trauma of an average peak overpressure of 14.6 psi, repeated across three consecutive days. While a single exposure did not reveal trauma as indicated by the glial fibrillary acidic protein indicator, three repetitive blasts did show significant increases. As well, mice had an increased indicator of inflammation (Iba-1) and increased tau, tau phosphorylation, and altered cytokine levels in the spleen. Video-electroencephalographic monitoring 48 h after the final blast exposure demonstrated seizures in 50% (12/24) of the mice, most of which were non-convulsive seizures. Long-term monitoring revealed that spontaneous seizures developed in at least 46% (6/13) of the mice. Patch clamp recording of dentate gyrus hippocampus neurons 48 h post-blast TBI demonstrated a shortened latency to the first spike and hyperpolarization of action potential threshold. We also found that evoked excitatory postsynaptic current amplitudes were significantly increased. These findings indicate that mild, repetitive blast exposures cause increases in neuronal excitability and seizures and eventual epilepsy development in some animals. The non-convulsive nature of the seizures suggests that subclinical seizures may occur in individuals experiencing even mild blast events, if repeated.

KCNMA1-linked channelopathy

Bailey et al. review a new neurological channelopathy associated with KCNMA1, encoding the BK voltage- and Ca²⁺-activated K⁺ channel.

KCNMA1 encodes the pore-forming α subunit of the “Big K⁺” (BK) large conductance calcium and voltage-activated K⁺ channel. BK channels are widely distributed across tissues, including both excitable and nonexcitable cells. Expression levels are highest in brain and muscle, where BK channels are critical regulators of neuronal excitability and muscle contractility. A global deletion in mouse (KCNMA1^−/−) is viable but exhibits pathophysiology in many organ systems. Yet despite the important roles in animal models, the consequences of dysfunctional BK channels in humans are not well characterized. Here, we summarize 16 rare KCNMA1 mutations identified in 37 patients dating back to 2005, with an array of clinically defined pathological phenotypes collectively referred to as “KCNMA1-linked channelopathy.” These mutations encompass gain-of-function (GOF) and loss-of-function (LOF) alterations in BK channel activity, as well as several variants of unknown significance (VUS). Human KCNMA1 mutations are primarily associated with neurological conditions, including seizures, movement disorders, developmental delay, and intellectual disability. Due to the recent identification of additional patients, the spectrum of symptoms associated with KCNMA1 mutations has expanded but remains primarily defined by brain and muscle dysfunction. Emerging evidence suggests the functional BK channel alterations produced by different KCNMA1 alleles may associate with semi-distinct patient symptoms, such as paroxysmal nonkinesigenic dyskinesia (PNKD) with GOF and ataxia with LOF. However, due to the de novo origins for the majority of KCNMA1 mutations identified to date and the phenotypic variability exhibited by patients, additional evidence is required to establish causality in most cases. The symptomatic picture developing from patients with KCNMA1-linked channelopathy highlights the importance of better understanding the roles BK channels play in regulating cell excitability. Establishing causality between KCNMA1-linked BK channel dysfunction and specific patient symptoms may reveal new treatment approaches with the potential to increase therapeutic efficacy over current standard regimens.

KCNMB3 in spinal microglia contributes to the generation and maintenance of neuropathic pain in mice

Neuropathic pain is one of most intense types of chronic pain. Numerous studies investigating neuropathic pain have described the critical involvement of microglia in the spinal cord. Previous studies have indicated that activation of large conductance Ca2+‑activated K+ (BK) channels contributes to microglial activation in the spinal dorsal horn (SDH) and the generation of neuropathic pain. However, the specific role of BK channels in spinal microglia in neuropathic pain has not been fully addressed in previous studies, as BK channel inhibitors were used to inhibit microglial BK channel based on their inhibitory kinetics. We previously identified that Ca2+‑activated K+ channel β3 auxiliary subunit (KCNMB3), which is an auxiliary subunit of BK channels and regulates gating properties of the channel, is exclusively expressed in microglia in the spinal cord. The present study analyzed the role of BK channels in spinal microglia in neuropathic pain using a spinal microglia‑specific BK channel knockdown method, with intrathecal injection of KCNMB3 small interfering RNA. Neuropathic pain was significantly attenuated in KCNMB3 knockdown mice. Increases in the number of microglia in the SDH following nerve injury were attenuated by KCNMB3 knockdown. Furthermore, increased levels of pain‑associated molecules in the SDH were attenuated in KCNMB3 knockdown mice. Attempts were also made to analyze the effects of KCNMB3 knockdown on chronic pain. KCNMB3 knockdown ameliorated chronic pain and inhibited the expression levels of pain‑associated molecules in the SDH. The results from the present study suggested that BK channels modulated the activation state of spinal microglia, and that KCNMB3 is a potential therapeutic target for neuropathic pain.

The molecular nature of the 17β-Estradiol binding site in the voltage- and Ca2+-activated K+ (BK) channel β1 subunit

The accessory β1 subunit modulates the Ca2+- and voltage-activated K+ (BK) channel gating properties mainly by increasing its apparent Ca2+ sensitivity. β1 plays an important role in the modulation of arterial tone and blood pressure by vascular smooth muscle cells (SMCs). 17β-estradiol (E2) increases the BK channel open probability (Po) in SMCs, through a β1 subunit-dependent modulatory effect. Here, using molecular modeling, bioinformatics, mutagenesis, and electrophysiology, we identify a cluster of hydrophobic residues in the second transmembrane domain of the β1 subunit, including the residues W163 and F166, as the binding site for E2. We further show that the increase in Po induced by E2 is associated with a stabilization of the voltage sensor in its active configuration and an increase in the coupling between the voltage sensor activation and pore opening. Since β1 is a key molecular player in vasoregulation, the findings reported here are of importance in the design of novel drugs able to modulate BK channels.

The Cannabinoid-Like Compound, VSN16R, Acts on Large Conductance, Ca2+-Activated K+ Channels to Modulate Hippocampal CA1 Pyramidal Neuron Firing

Large conductance, Ca2+-activated K+ (BKCa) channels are widely expressed in the central nervous system, where they regulate action potential duration, firing frequency and consequential neurotransmitter release. Moreover, drug action on, mutations to, or changes in expression levels of BKCa can modulate neuronal hyperexcitability. Amongst other potential mechanisms of action, cannabinoid compounds have recently been reported to activate BKCa channels. Here, we examined the effects of the cannabinoid-like compound (R,Z)-3-(6-(dimethylamino)-6-oxohex-1-en-1-yl)-N-(1-hydroxypropan-2-yl) benzamide (VSN16R) at CA1 pyramidal neurons in hippocampal ex vivo brain slices using current clamp electrophysiology. We also investigated effects of the BKCa channel blockers iberiotoxin (IBTX) and the novel 7-pra-martentoxin (7-Pra-MarTx) on VSN16R action. VSN16R (100 μM) increased first and second fast after-hyperpolarization (fAHP) amplitude, decreased first and second inter spike interval (ISI) and shortened first action potential (AP) width under high frequency stimulation protocols in mouse hippocampal pyramidal neurons. IBTX (100 nM) decreased first fAHP amplitude, increased second ISI and broadened first and second AP width under high frequency stimulation protocols; IBTX also broadened first and second AP width under low frequency stimulation protocols. IBTX blocked effects of VSN16R on fAHP amplitude and ISI. 7-Pra-MarTx (100 nM) had no significant effects on fAHP amplitude and ISI but, unlike IBTX, shortened first and second AP width under high frequency stimulation protocols; 7-Pra-MarTx also shortened second AP width under low frequency stimulation protocols. However, in the presence of 7-Pra-MarTx, VSN16R retained some effects on AP waveform under high frequency stimulation protocols; moreover, VSN16R effects were revealed under low frequency stimulation protocols. These findings demonstrate that VSN16R has effects in native hippocampal neurons consistent with its causing an increase in initial firing frequency via activation of IBTX-sensitive BKCa channels. The differential pharmacological effects described suggest that VSN16R may differentially target BKCa channel subtypes.

The absence of NIPA2 enhances neural excitability through BK (big potassium) channels

AIM

To reveal the pathogenesis and find the precision treatment for the childhood absence epilepsy (CAE) patients with NIPA2 mutations.

METHODS

We performed whole-cell patch-clamp recordings to measure the electrophysiological properties of layer V neocortical somatosensory pyramidal neurons in wild-type (WT) and NIPA2-knockout mice.

RESULTS

We identified that layer V neocortical somatosensory pyramidal neurons isolated from the NIPA2-knockout mice displayed higher frequency of spontaneous and evoked action potential, broader half-width of evoked action potential, and smaller currents of BK channels than those from the WT mice. NS11021, a specific BK channel opener, reduced neuronal excitability in the NIPA2-knockout mice. Paxilline, a selective BK channel blocker, treated WT neurons and could simulate the situation of NIPA2-knockout group, thereby suggesting that the absence of NIPA2 enhanced the excitability of neocortical somatosensory pyramidal neurons by decreasing the currents of BK channels. Zonisamide, an anti-epilepsy drug, reduced action potential firing in NIPA2-knockout mice through increasing BK channel currents.

CONCLUSION

The results indicate that the absence of NIPA2 enhances neural excitability through BK channels. Zonisamide is probably a potential treatment for NIPA2 mutation-induced epilepsy, which may provide a basis for the development of new treatment strategies for epilepsy.