Sorbs2 Deficiency and Vascular BK Channelopathy in Diabetes.

BACKGROUND: Vascular large conductance Ca2+-activated K+ (BK) channel, composed of the α-subunit (BK-α) and the ß1-subunit (BK-ß1), is a key determinant of coronary vasorelaxation and its function is impaired in diabetic vessels. However, our knowledge of diabetic BK channel dysregulation is incomplete. The Sorbs2 (Sorbin homology [SoHo] and Src homology 3 [SH3] domains-containing protein 2), is ubiquitously expressed in arteries, but its role in vascular pathophysiology is unknown. METHODS: The role of Sorbs2 in regulating vascular BK channel activity was determined using patch-clamp recordings, molecular biological techniques, and in silico analysis. RESULTS: Sorbs2 is not only a cytoskeletal protein but also an RNA-binding protein that binds to BK channel proteins and BK-α mRNA, regulating BK channel expression and function in coronary smooth muscle cells. Molecular biological studies reveal that the SH3 domain of Sorbs2 is necessary for Sorbs2 interaction with BK-α subunits, while both the SH3 and SoHo domains of Sorbs2 interact with BK-ß1 subunits. Deletion of the SH3 or SoHo domains abolishes the Sorbs2 effect on the BK-α/BK-ß1 channel current density. Additionally, Sorbs2 is a target gene of the Nrf2 (nuclear factor erythroid-2-related factor 2), which binds to the promoter of Sorbs2 and regulates Sorbs2 expression in coronary smooth muscle cells. In vivo studies demonstrate that Sorbs2 knockout mice at 4 months of age display a significant decrease in BK channel expression and function, accompanied by impaired BK channel Ca2+-sensitivity and BK channel-mediated vasodilation in coronary arteries, without altering their body weights and blood glucose levels. Importantly, Sorbs2 expression is significantly downregulated in the coronary arteries of db/db type 2 diabetic mice. CONCLUSIONS: Sorbs2, a downstream target of Nrf2, plays an important role in regulating BK channel expression and function in vascular smooth muscle cells. Vascular Sorbs2 is downregulated in diabetes. Genetic knockout of Sorbs2 manifests coronary BK channelopathy and vasculopathy observed in diabetic mice, independent of obesity and glucotoxicity.

Progesterone activation of ß1-containing BK channels involves two binding sites.

Progesterone (≥1 µM) is used in recovery of cerebral ischemia, an effect likely contributed to by cerebrovascular dilation. The targets of this progesterone action are unknown. We report that micromolar (µM) progesterone activates mouse cerebrovascular myocyte BK channels; this action is lost in ß1-/- mice myocytes and in lipid bilayers containing BK α subunit homomeric channels but sustained on ß1/ß4-containing heteromers. Progesterone binds to both regulatory subunits, involving two steroid binding sites conserved in ß1-ß4: high-affinity (sub-µM), which involves Trp87 in ß1 loop, and low-affinity (µM) defined by TM1 Tyr32 and TM2 Trp163. Thus progesterone, but not its oxime, bridges TM1-TM2. Mutation of the high-affinity site blunts channel activation by progesterone underscoring a permissive role of the high-affinity site: progesterone binding to this site enables steroid binding at the low-affinity site, which activates the channel. In support of our model, cerebrovascular dilation evoked by µM progesterone is lost by mutating Tyr32 or Trp163 in ß1 whereas these mutations do not affect alcohol-induced cerebrovascular constriction. Furthermore, this alcohol action is effectively counteracted both in vitro and in vivo by progesterone but not by its oxime.

Interspecies and regional variability of alcohol action on large cerebral arteries: regulation by KCNMB1 proteins.

Alcohol intake leading to blood ethanol concentrations (BEC) ≥ legal intoxication modifies brain blood flow with increases in some regions and decreases in others. Brain regions receive blood from the Willis' circle branches: anterior, middle (MCA) and posterior cerebral (PCA), and basilar (BA) arteries. Rats and mice have been used to identify the targets mediating ethanol-induced effects on cerebral arteries, with conclusions being freely interchanged, albeit data were obtained in different species/arterial branches. We tested whether ethanol action on cerebral arteries differed between male rat and mouse and/or across different brain regions and identified the targets of alcohol action. In both species and all Willis' circle branches, ethanol evoked reversible and concentration-dependent constriction (EC50s ≈ 37-86 mM; below lethal BEC in alcohol-naïve humans). Although showing similar constriction to depolarization, both species displayed differential responses to ethanol: in mice, MCA constriction was highly sensitive to the presence/absence of the endothelium, whereas in rat PCA was significantly more sensitive to ethanol than its mouse counterpart. In the rat, but not the mouse, BA was more ethanol sensitive than other branches. Both interspecies and regional variability were ameliorated by endothelium. Selective large conductance (BK) channel block in de-endothelialized vessels demonstrated that these channels were the effectors of alcohol-induced cerebral artery constriction across regions and species. Variabilities in alcohol actions did not fully matched KCNMB1 expression across vessels. However, immunofluorescence data from KCNMB1-/- mouse arteries electroporated with KCNMB1-coding cDNA demonstrate that KCNMB1 proteins, which regulate smooth muscle (SM) BK channel function and vasodilation, regulate interspecies and regional variability of brain artery responses to alcohol.

Dbx1 controls the development of astrocytes of the intermediate spinal cord by modulating Notch signaling.

Significant progress has been made in elucidating the basic principles that govern neuronal specification in the developing central nervous system. In contrast, much less is known about the origin of astrocytic diversity. Here, we demonstrate that a restricted pool of progenitors in the mouse spinal cord, expressing the transcription factor Dbx1, produces a subset of astrocytes, in addition to interneurons. Ventral p0-derived astrocytes (vA0 cells) exclusively populate intermediate regions of spinal cord with extraordinary precision. The postnatal vA0 population comprises gray matter protoplasmic and white matter fibrous astrocytes and a group of cells with strict radial morphology contacting the pia. We identified that vA0 cells in the lateral funiculus are distinguished by the expression of reelin and Kcnmb4. We show that Dbx1 mutants have an increased number of vA0 cells at the expense of p0-derived interneurons. Manipulation of the Notch pathway, together with the alteration in their ligands seen in Dbx1 knockouts, suggest that Dbx1 controls neuron-glial balance by modulating Notch-dependent cell interactions. In summary, this study highlights that restricted progenitors in the dorsal-ventral neural tube produce region-specific astrocytic subgroups and that progenitor transcriptional programs highly influence glial fate and are instrumental in creating astrocyte diversity.

Family-Based Cohort Association Study of PRKCB1, CBLN1 and KCNMB4 Gene Polymorphisms and Autism in Polish Population.

The aim of the study was to perform family-based association analysis of PRKCB1, CBLN1 and KCNMB4 gene polymorphisms and autism disorder. We comprised 206 Caucasian children with autistic spectrum disorder (ASD) and their biological parents. In transmission/disequilibrium test we observed that T-allele of the rs198198 polymorphism of the PRKCB1 gene was more often transmitted to affected children in the male subgroup (p = 0.010). Additionally, the T carrier state was significantly associated with hypotonia (p = 0.048). In the female subgroup, the T-allele carriers more often showed more mobile/vital behavior (p = 0.046). In conclusion, our study showed that the rs198198 of the PRKCB1 gene may be associated with ASD in men and with some features characteristic for the disorder.

Cholesterol activates BK channels by increasing KCNMB1 protein levels in the plasmalemma.

Calcium-/voltage-gated, large-conductance potassium channels (BKs) control critical physiological processes, including smooth muscle contraction. Numerous observations concur that elevated membrane cholesterol (CLR) inhibits the activity of homomeric BKs consisting of channel-forming alpha subunits. In mammalian smooth muscle, however, native BKs include accessory KCNMB1 (ß1) subunits, which enable BK activation at physiological intracellular calcium. Here, we studied the effect of CLR enrichment on BK currents from rat cerebral artery myocytes. Using inside-out patches from middle cerebral artery (MCA) myocytes at [Ca2+]free=30 µM, we detected BK activation in response to in vivo and in vitro CLR enrichment of myocytes. While a significant increase in myocyte CLR was achieved within 5 min of CLR in vitro loading, this brief CLR enrichment of membrane patches decreased BK currents, indicating that BK activation by CLR requires a protracted cellular process. Indeed, blocking intracellular protein trafficking with brefeldin A (BFA) not only prevented BK activation but led to channel inhibition upon CLR enrichment. Surface protein biotinylation followed by Western blotting showed that BFA blocked the increase in plasmalemmal KCNMB1 levels achieved via CLR enrichment. Moreover, CLR enrichment of arteries with naturally high KCNMB1 levels, such as basilar and coronary arteries, failed to activate BK currents. Finally, CLR enrichment failed to activate BK channels in MCA myocytes from KCNMB1-/- mouse while activation was detected in their wild-type (C57BL/6) counterparts. In conclusion, the switch in CLR regulation of BK from inhibition to activation is determined by a trafficking-dependent increase in membrane levels of KCNMB1 subunits.

Arachidonic acid effect on the allosteric gating mechanism of BK (Slo1) channels associated with the ß1 subunit.

Arachidonic acid (AA) is a fatty acid involved in the modulation of several ion channels. Previously, we reported that AA activates the high conductance Ca2+- and voltage-dependent K+ channel (BK) in vascular smooth muscle depending on the expression of the auxiliary ß1 subunit. Here, using the patch-clamp technique on BK channel co-expressed with ß1 subunit in a heterologous cell expression system, we analyzed whether AA modifies the three functional modules involved in the channel gating: the voltage sensor domain (VSD), the pore domain (PD), and the intracellular calcium sensor domain (CSD). We present evidence that AA activates BK channel in a direct way, inducing VSD stabilization on its active configuration observed as a significant left shift in the Q-V curve obtained from gating currents recordings. Moreover, AA facilitates the channel opening transitions when VSD are at rest, and the CSD are unoccupied. Furthermore, the activation was independent of the intracellular Ca2+ concentration and reduced when the BK channel was co-expressed with the Y74A mutant of the ß1 subunit. These results allow us to present new insigths in the mechanism by which AA modulates BK channels co-expressed with its auxiliary ß1 subunit.

Ryanodine receptor subtypes regulate Ca2+ sparks/spontaneous transient outward currents and myogenic tone of uterine arteries in pregnancy.

AIMS: Our recent study demonstrated that increased Ca2+ sparks and spontaneous transient outward currents (STOCs) played an important role in uterine vascular tone and haemodynamic adaptation to pregnancy. The present study examined the role of ryanodine receptor (RyR) subtypes in regulating Ca2+ sparks/STOCs and myogenic tone in uterine arterial adaptation to pregnancy. METHODS AND RESULTS: Uterine arteries isolated from non-pregnant and near-term pregnant sheep were used in the present study. Pregnancy increased the association of α and ß1 subunits of large-conductance Ca2+-activated K+ (BKCa) channels and enhanced the co-localization of RyR1 and RyR2 with the ß1 subunit in the uterine artery. In contrast, RyR3 was not co-localized with BKCa ß1 subunit. Knockdown of RyR1 or RyR2 in uterine arteries of pregnant sheep downregulated the ß1 but not α subunit of the BKCa channel and decreased the association of α and ß1 subunits. Unlike RyR1 and RyR2, knockdown of RyR3 had no significant effect on either expression or association of BKCa subunits. In addition, knockdown of RyR1 or RyR2 significantly decreased Ca2+ spark frequency, suppressed STOCs frequency and amplitude, and increased pressure-dependent myogenic tone in uterine arteries of pregnant animals. RyR3 knockdown did not affect Ca2+ sparks/STOCs and myogenic tone in the uterine artery. CONCLUSION: Together, the present study demonstrates a novel mechanistic paradigm of RyR subtypes in the regulation of Ca2+ sparks/STOCs and uterine vascular tone, providing new insights into the mechanisms underlying uterine vascular adaptation to pregnancy.

The potassium channel subunit Kvß1 serves as a major control point for synaptic facilitation.

Analysis of the presynaptic action potential's (APsyn) role in synaptic facilitation in hippocampal pyramidal neurons has been difficult due to size limitations of axons. We overcame these size barriers by combining high-resolution optical recordings of membrane potential, exocytosis, and Ca2+ in cultured hippocampal neurons. These recordings revealed a critical and selective role for Kv1 channel inactivation in synaptic facilitation of excitatory hippocampal neurons. Presynaptic Kv1 channel inactivation was mediated by the Kvß1 subunit and had a surprisingly rapid onset that was readily apparent even in brief physiological stimulation paradigms including paired-pulse stimulation. Genetic depletion of Kvß1 blocked all broadening of the APsyn during high-frequency stimulation and eliminated synaptic facilitation without altering the initial probability of vesicle release. Thus, using all quantitative optical measurements of presynaptic physiology, we reveal a critical role for presynaptic Kv channels in synaptic facilitation at presynaptic terminals of the hippocampus upstream of the exocytic machinery.

Long Noncoding RNA KCNMB2-AS1 Stabilized by N6-Methyladenosine Modification Promotes Cervical Cancer Growth Through Acting as a Competing Endogenous RNA.

Long noncoding RNA (lncRNA) is emerging as an essential regulator in the development and progression of cancer, including cervical cancer (CC). In this study, we found a CC-related lncRNA, KCNMB2-AS1, which was significantly overexpressed in CC and linked to poor outcomes. Depletion of KCNMB2-AS1 remarkably inhibited CC cell proliferation and induced apoptosis. In vivo xenograft models revealed that knockdown of KCNMB2-AS1 evidently delayed tumor growth. Mechanistically, KCNMB2-AS1 was predominantly located in the cytoplasm and served as a competing endogenous RNA to abundantly sponge miR-130b-5p and miR-4294, resulting in the upregulation of IGF2BP3, a well-documented oncogene in CC. Moreover, IGF2BP3 was able to bind KCNMB2-AS1 by three N6-methyladenosine (m6A) modification sites on KCNMB2-AS1, in which IGF2BP3 acted as an m6A "reader" and stabilized KCNMB2-AS1. Thus, KCNMB2-AS1 and IGF2BP3 formed a positive regulatory circuit that enlarged the tumorigenic effect of KCNMB2-AS1 in CC. Together, our data clearly suggest that KCNMB2-AS1 is a novel oncogenic m6A-modified lncRNA in CC, targeting KCNMB2-AS1 and its related molecules implicate the therapeutic possibility for CC patients.

Antenatal Dexamethasone Exposure Impairs the High-Conductance Ca2+-Activated K+ Channels via Epigenetic Alteration at Gene Promoter in Male Offspring.

OBJECTIVE: Antenatal exposure to glucocorticoids increases cardiovascular risks related to vascular dysfunctions in offspring, although underlying mechanisms are still unknown. As an important vascular mediator, high-conductance Ca2+-activated K+ channels (BK) plays an essential role in determining vascular tone. Long-term effects of antenatal glucocorticoids on BK in offspring are largely unknown. This study examined the effects and mechanisms of antenatal exposure to clinically relevant doses of glucocorticoids on vascular BK in offspring. Approach and Results: Pregnant Sprague-Dawley rats received synthetic glucocorticoids dexamethasone or vehicle during the last week of pregnancy. Vascular functions, cellular electrophysiology, target gene expression, and promoter methylation were examined in mesenteric arteries of male offspring (gestational day 21 [fetus] and postnatal day 120 [adult offspring]). Antenatal dexamethasone exposure impaired BK activators-mediated relaxation and reduced whole-cell BK currents in mesenteric arteries. Antenatal dexamethasone exposure did not alter Ca2+/voltage-sensitivity of BK but downregulated the expressions of BK α and ß1 subunits in both fetal and adult mesenteric arteries. In addition, increased promoter methylations within BKα and BKß1 were compatible with reduced expressions of the 2 genes. CONCLUSIONS: Our findings showed a profound and long-term impact of antenatal dexamethasone exposure on vascular BK via an altered epigenetic pattern from fetal stage to adulthood, advancing understanding of prolonged adverse effects and mechanisms of antenatal glucocorticoids exposure on vascular health in offspring.

Regulation of KCNMA1 transcription by Nrf2 in coronary arterial smooth muscle cells.

The large conductance Ca2+-activated K+ (BK) channels, composed of the pore-forming α subunits (BK-α, encoded by KCNMA1 gene) and the regulatory ß1 subunits (BK-ß1, encoded by KCNMB1 gene), play a unique role in the regulation of coronary vascular tone and myocardial perfusion by linking intracellular Ca2+ homeostasis with excitation-contraction coupling in coronary arterial smooth muscle cells (SMCs). The nuclear factor erythroid 2-related factor 2 (Nrf2) belongs to a member of basic leucine zipper transcription factor family that regulates the expression of antioxidant and detoxification enzymes by binding to the antioxidant response elements (AREs) of these target genes. We have previously reported that vascular BK-ß1 protein expression was tightly regulated by Nrf2. However, the molecular mechanism underlying the regulation of BK channel expression by Nrf2, particularly at transcription level, is unknown. In this study, we hypothesized that KCNMA1 and KCNMB1 are the target genes of Nrf2 transcriptional regulation. We found that BK channel protein expression and current density were diminished in freshly isolated coronary arterial SMCs of Nrf2 knockout (KO) mice. However, BK-α mRNA expression was reduced, but not that of BK-ß1 mRNA expression, in the arteries of Nrf2 KO mice. Promoter-Nrf2 luciferase reporter assay confirmed that Nrf2 binds to the ARE of KCNMA1 promoter, but not that of KCNMB1. Adenoviral expression and pharmacological activation of Nrf2 increased BK-α and BK-ß1 protein levels and enhanced BK channel activity in coronary arterial SMCs. Hence, our results indicate that Nrf2 is a key determinant of BK channel expression and function in vascular SMCs. Nrf2 facilitates BK-α expression through a direct increase in gene transcription, whereas that on BK-ß1 is through a different mechanism.

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 BKCa channels, are ubiquitously expressed throughout the central nervous system including the cingulate cortex. However, what changes of cortical BKCa channels undergo in the ACC remains unknown in pain-related anxiety. In the present study, a significant upregulation of synaptic and non-synaptic BKCa channel accessory ß4 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 BKCa channels, significantly rescued the alteration of fAHP and AP duration of ACC pyramidal neurons in mCCD rats. The mRNA expression of BKCa ß4 subunits was extremely upregulated in the ACC after mCCD with the increased amount of both synaptic and non-synaptic BKCa ß4 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 BKCa channels in the ACC reversed mechanical allodynia and anxiety-like behaviors. These results suggest that the upregulation of postsynaptic and presynaptic BKCa ß4 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.

The Role of KCNMB1 and BK Channels in Myofibroblast Differentiation and Pulmonary Fibrosis.

The differentiation of fibroblasts into myofibroblasts is critical for the development of fibrotic disorders, including idiopathic pulmonary fibrosis (IPF). Previously, we demonstrated that fibroblasts from patients with IPF exhibit changes in DNA methylation across the genome that contribute to a profibrotic phenotype. One of the top differentially methylated genes identified in our previous study was KCNMB1, which codes for the ß subunit of the large-conductance potassium (BK, also known as MaxiK or KCa1.1) channel. Here, we examined how the expression of KCNMB1 differed between IPF fibroblasts and normal cells, and how BK channels affected myofibroblast differentiation. Fibroblasts from patients with IPF exhibited increased expression of KCNMB1, which corresponded to increased DNA methylation within the gene body. Patch-clamp experiments demonstrated that IPF fibroblasts had increased BK channel activity. Knockdown of KCNMB1 attenuated the ability of fibroblasts to contract collagen gels, and this was associated with a loss of α-smooth muscle actin (SMA) expression. Pharmacologic activation of BK channels stimulated α-SMA expression, whereas BK channel inhibitors blocked the upregulation of α-SMA. The ability of BK channels to enhance α-SMA expression was dependent on intracellular calcium, as activation of BK channels resulted in increased levels of intracellular calcium and the effects of BK agonists were abolished when calcium was removed. Together, our findings demonstrate that epigenetic upregulation of KCNMB1 contributes to increased BK channel activity in IPF fibroblasts, and identify a newfound role for BK channels in myofibroblast differentiation.

Aging influences cerebrovascular myogenic reactivity and BK channel function in a sex-specific manner.

AIMS: The myogenic reactivity of the middle cerebral arteries (MCA) protects the brain by altering the diameter in response to changes in lumen pressure. Large conductance potassium (BK) channels are known to regulate the myogenic reactivity, yet, it is not clear how aging alters the myogenic reactivity via the BK channel in males and females. Thus, we hypothesize that age-associated changes in BK channel subunits modulate the myogenic reactivity in a sex-specific manner. METHODS AND RESULTS: We used vascular reactivity, patch-clamp, and biochemical methods to measure myogenic reactivity, BK channel function, and expression, respectively in cerebral vessels of adult and aged male and female Sprague Dawley rats. Our results suggest that aging and ovariectomy (OVX) exaggerated the myogenic reactivity of MCA in females but attenuated it in males. Aging induced outward eutrophic remodelling in females but inward hypertrophic remodelling in males. Aging decreased total, Kv, BK channel currents, and spontaneous transient outward currents (STOC) in vascular smooth muscle cells isolated from females, but not in males. Aging increased BKα subunit mRNA and protein both in males and females. However, aging decreased BKß1 subunit protein and mRNA in females only. In males, BKß1 mRNA is increased, but protein is decreased. Iberiotoxin-induced MCA constriction is lower in aged females but higher in aged males. Activation of BKα (10 µM NS1619) and BKß1 (10 µM S-Equol) subunits failed to increase STOCs and were unable to decrease the myogenic reactivity of MCA in aged female but not in aged male rats. OVX decreased, but chronic supplementation of oestradiol restored BK channel expression and function. CONCLUSION: Overall our results suggest that aging or OVX-associated downregulation of the BKß1 expression and function in females results in exaggerated myogenic reactivity of MCA. However, age-associated increase in BK channel function in males attenuated myogenic reactivity of MCA.

Selective Blockade of Neuronal BK (α + ß4) Channels Preventing Epileptic Seizure.

Gain-of-function of BK channels or knockout of their ß4 subunit is associated with spontaneous epilepsy. Currently, efficacy of BK (α + ß4) channel modulators in preventing epilepsy was never reported. Here, we show that martentoxin selectively inhibits BK (α + ß4) channels by interaction with the extracellular loop of the BK ß4 subunit (hß4-loop) at a molar ratio 4:1 (hß4-loop vs martentoxin). Residues Glu104, Glu122, Gln124, Lys125, and Glu128 of the hß4-loop form hydrogen bonds with residues Asp5, Glu13, Lys20, Ser24, Gln26, Lys28, and Arg35 of martentoxin, by which martentoxin reduces the neuronal spiking frequency and increases interspike intervals. Intrahippocampal infusion of martentoxin significantly increases the latency time of seizure, reduces seizure duration and seizure numbers on pentylenetetrazole-induced presensitized rats, inhibits hippocampal hyperexcitability and c-Fos expression, and displays neuroprotective effects on hippocampal neurons. These results suggest that the BK (α + ß4) channel is a novel therapeutic target of intractable epilepsy and martentoxin contributes to the rational drug design for epilepsy treatment.

Attenuated BK channel function promotes overactive bladder in a rat model of obesity.

Overactive bladder (OAB) is mostly observed in obese individuals, and is associated with enhanced excitability and contractility of the detrusor smooth muscle (DSM). Large-conductance voltage- and Ca2+-activated K+ (BK) channels reduce the excitability and contractility of the DSM. We tested whether obesity-induced OAB is associated with altered BK channel expression and activity in the DSM. Seven-week-old female Sprague-Dawley rats (N=80) were fed a normal or high-fat diet (HFD) for 12 weeks. HFD-fed rats exhibited a higher average bodyweight and urodynamically established detrusor overactivity. mRNA levels of the Kcnma1 (BKα subunit) and Kcnmb1 (BKß1 subunit) in whole tissues and cells from the DSM were reduced in HFD-fed rats. A selective BK channel opener, NS1619, was then applied to DSM cells from the two groups of rats. Patch-clamp techniques revealed that spontaneous transient outward currents, NS1619-induced activation of spontaneous transient outward currents, and whole-cell BK currents, as well as NS1619-induced membrane hyperpolarization, were attenuated in DSM cells from HFD-fed rats. The relaxation effect of NS1619 on contractility was reduced in DSM strips from HFD-fed rats. Thus, impaired expression of Kcnma1 and Kcnmb1 in the DSM contributes to obesity-induced OAB, suggesting that BK channels could be a useful treatment targets in OAB.

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 ß3 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 microglia­specific 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 pain­associated 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 pain­associated 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.

S-Acylation controls functional coupling of BK channel pore-forming α-subunits and ß1-subunits.

The properties and physiological function of pore-forming α-subunits of large conductance calcium- and voltage-activated potassium (BK) channels are potently modified by their functional coupling with regulatory subunits in many tissues. However, mechanisms that might control functional coupling are very poorly understood. Here we show that S-acylation, a dynamic post-translational lipid modification of proteins, of the intracellular S0-S1 loop of the BK channel pore-forming α-subunit controls functional coupling to regulatory ß1-subunits. In HEK293 cells, α-subunits that cannot be S-acylated show attenuated cell surface expression, but expression was restored by co-expression with the ß1-subunit. However, we also found that nonacylation of the S0-S1 loop reduces functional coupling between α- and ß1-subunits by attenuating the ß1-subunit-induced left shift in the voltage for half-maximal activation. In mouse vascular smooth muscle cells expressing both α- and ß1-subunits, BK channel α-subunits were endogenously S-acylated. We further noted that S-acylation is significantly reduced in mice with a genetic deletion of the palmitoyl acyltransferase (Zdhhc23) that controls S-acylation of the S0-S1 loop. Genetic deletion of Zdhhc23 or broad-spectrum pharmacological inhibition of S-acylation attenuated endogenous BK channel currents independently of changes in cell surface expression of the α-subunit. We conclude that functional effects of S-acylation on BK channels depend on the presence of ß1-subunits. In the absence of ß1-subunits, S-acylation promotes cell surface expression, whereas in its presence, S-acylation controls functional coupling. S-Acylation thus provides a mechanism that dynamically regulates the functional coupling with ß1-subunits, enabling an additional level of conditional, cell-specific control of ion-channel physiology.

MitoBKCa channel is functionally associated with its regulatory ß1 subunit in cardiac mitochondria.

KEY POINTS: Association of plasma membrane BKCa channels with BK-ß subunits shapes their biophysical properties and physiological roles; however, functional modulation of the mitochondrial BKCa channel (mitoBKCa ) by BK-ß subunits is not established. MitoBKCa -α and the regulatory BK-ß1 subunit associate in mouse cardiac mitochondria. A large fraction of mitoBKCa display properties similar to that of plasma membrane BKCa when associated with BK-ß1 (left-shifted voltage dependence of activation, V1/2  = -55 mV, 12 µm matrix Ca2+ ). In BK-ß1 knockout mice, cardiac mitoBKCa displayed a low Po and a depolarized V1/2 of activation (+47 mV at 12 µm matrix Ca2+ ) Co-expression of BKCa with the BK-ß1 subunit in HeLa cells doubled the density of BKCa in mitochondria. The present study supports the view that the cardiac mitoBKCa channel is functionally modulated by the BK-ß1 subunit; proper targeting and activation of mitoBKCa shapes mitochondrial Ca2+ handling. ABSTRACT: Association of the plasma membrane BKCa channel with auxiliary BK-ß1-4 subunits profoundly affects the regulatory mechanisms and physiological processes in which this channel participates. However, functional association of mitochondrial BK (mitoBKCa ) with regulatory subunits is unknown. We report that mitoBKCa functionally associates with its regulatory subunit BK-ß1 in adult rodent cardiomyocytes. Cardiac mitoBKCa is a calcium- and voltage-activated channel that is sensitive to paxilline with a large conductance for K+ of 300 pS. Additionally, mitoBKCa displays a high open probability (Po ) and voltage half-activation (V1/2  = -55 mV, n = 7) resembling that of plasma membrane BKCa when associated with its regulatory BK-ß1 subunit. Immunochemistry assays demonstrated an interaction between mitochondrial BKCa -α and its BK-ß1 subunit. Mitochondria from the BK-ß1 knockout (KO) mice showed sparse mitoBKCa currents (five patches with mitoBKCa activity out of 28 total patches from n = 5 different hearts), displaying a depolarized V1/2 of activation (+47 mV in 12 µm matrix Ca2+ ). The reduced activity of mitoBKCa was accompanied by a high expression of BKCa transcript in the BK-ß1 KO, suggesting a lower abundance of mitoBKCa channels in this genotype. Accordingly, BK-ß1subunit increased the localization of BKDEC (i.e. the splice variant of BKCa that specifically targets mitochondria) into mitochondria by two-fold. Importantly, both paxilline-treated and BK-ß1 KO mitochondria displayed a more rapid Ca2+ overload, featuring an early opening of the mitochondrial transition pore. We provide strong evidence that mitoBKCa associates with its regulatory BK-ß1 subunit in cardiac mitochondria, ensuring proper targeting and activation of the mitoBKCa channel that helps to maintain mitochondrial Ca2+ homeostasis.