scholarly journals Regulation of BK Channels by Beta and Gamma Subunits

2019 ◽  
Vol 81 (1) ◽  
pp. 113-137 ◽  
Author(s):  
Vivian Gonzalez-Perez ◽  
Christopher J. Lingle
Keyword(s):  
Functional Properties ◽  
Splice Variants ◽  
Bk Channels ◽  
Bk Channel ◽  
Diverse Range ◽  
Α Subunit ◽  
Regulatory Subunits ◽  
Gamma Subunits ◽  
Specific Alternative ◽  
Alternative Splice Variants

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.

scholarly journals Effect of aldosterone on BK channel expression in mammalian cortical collecting duct

2008 ◽  
Vol 295 (3) ◽  
pp. F780-F788 ◽  
Author(s):  
Genevieve Estilo ◽  
Wen Liu ◽  
Nuria Pastor-Soler ◽  
Phillip Mitchell ◽  
Marcelo D. Carattino ◽  
...  
Keyword(s):  
Splice Variants ◽  
Collecting Duct ◽  
Bk Channels ◽  
Bk Channel ◽  
Mrna Abundance ◽  
Cortical Collecting Duct ◽  
Α Subunit ◽  
Channel Expression ◽  
Tubular Flow ◽  
Circulating Levels

Apical large-conductance Ca2+-activated K+ (BK) channels in the cortical collecting duct (CCD) mediate flow-stimulated K+ secretion. Dietary K+ loading for 10–14 days leads to an increase in BK channel mRNA abundance, enhanced flow-stimulated K+ secretion in microperfused CCDs, and a redistribution of immunodetectable channels from an intracellular pool to the apical membrane (Najjar F, Zhou H, Morimoto T, Bruns JB, Li HS, Liu W, Kleyman TR, Satlin LM. Am J Physiol Renal Physiol 289: F922–F932, 2005). To test whether this adaptation was mediated by a K+-induced increase in aldosterone, New Zealand White rabbits were fed a low-Na+ (LS) or high-Na+ (HS) diet for 7–10 days to alter circulating levels of aldosterone but not serum K+ concentration. Single CCDs were isolated for quantitation of BK channel subunit (total, α-splice variants, β-isoforms) mRNA abundance by real-time PCR and measurement of net transepithelial Na+ (JNa) and K+ (JK) transport by microperfusion; kidneys were processed for immunolocalization of BK α-subunit by immunofluorescence microscopy. At the time of death, LS rabbits excreted no urinary Na+ and had higher circulating levels of aldosterone than HS animals. The relative abundance of BK α-, β2-, and β4-subunit mRNA and localization of immunodetectable α-subunit were similar in CCDs from LS and HS animals. In response to an increase in tubular flow rate from ∼1 to 5 nl·min−1·mm−1, the increase in JNa was greater in LS vs. HS rabbits, yet the flow-stimulated increase in JK was similar in both groups. These data suggest that aldosterone does not contribute to the regulation of BK channel expression/activity in response to dietary K+ loading.

scholarly journals Regulatory γ1 subunits defy symmetry in functional modulation of BK channels

2018 ◽  
Vol 115 (40) ◽  
pp. 9923-9928 ◽  
Author(s):  
Vivian Gonzalez-Perez ◽  
Manu Ben Johny ◽  
Xiao-Ming Xia ◽  
Christopher J. Lingle
Keyword(s):  
Single Channel ◽  
Regulatory Protein ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Bk Channels ◽  
Bk Channel ◽  
Single Type ◽  
Regulatory Subunits ◽  
And Function

Structural symmetry is a hallmark of homomeric ion channels. Nonobligatory regulatory proteins can also critically define the precise functional role of such channels. For instance, the pore-forming subunit of the large conductance voltage and calcium-activated potassium (BK, Slo1, or KCa1.1) channels encoded by a single KCa1.1 gene assembles in a fourfold symmetric fashion. Functional diversity arises from two families of regulatory subunits, β and γ, which help define the range of voltages over which BK channels in a given cell are activated, thereby defining physiological roles. A BK channel can contain zero to four β subunits per channel, with each β subunit incrementally influencing channel gating behavior, consistent with symmetry expectations. In contrast, a γ1 subunit (or single type of γ1 subunit complex) produces a functionally all-or-none effect, but the underlying stoichiometry of γ1 assembly and function remains unknown. Here we utilize two distinct and independent methods, a Forster resonance energy transfer-based optical approach and a functional reporter in single-channel recordings, to reveal that a BK channel can contain up to four γ1 subunits, but a single γ1 subunit suffices to induce the full gating shift. This requires that the asymmetric association of a single regulatory protein can act in a highly concerted fashion to allosterically influence conformational equilibria in an otherwise symmetric K+channel.

β-Subunit–Dependent Modulation of hSlo BK Current by Arachidonic Acid

2007 ◽  
Vol 97 (1) ◽  
pp. 62-69 ◽  
Author(s):  
X. Sun ◽  
D. Zhou ◽  
P. Zhang ◽  
E. G. Moczydlowski ◽  
G. G. Haddad
Keyword(s):  
Fatty Acids ◽  
Arachidonic Acid ◽  
Conformational Changes ◽  
Unsaturated Fatty Acids ◽  
Saturated Fatty Acids ◽  
Nordihydroguaiaretic Acid ◽  
Bk Channels ◽  
Bk Channel ◽  
Β Subunit ◽  
Α Subunit

In this study, we examined the effect of arachidonic acid (AA) on the BK α-subunit with or without β-subunits expressed in Xenopus oocytes. In excised patches, AA potentiated the hSlo-α current and slowed inactivation only when β2/3 subunit was co-expressed. The β2-subunit–dependent modulation by AA persisted in the presence of either superoxide dismutase or inhibitors of AA metabolism such as nordihydroguaiaretic acid and eicosatetraynoic acid, suggesting that AA acts directly rather than through its metabolites. Other cis unsaturated fatty acids (docosahexaenoic and oleic acid) also enhanced hSlo-α + β2 currents and slowed inactivation, whereas saturated fatty acids (palmitic, stearic, and caprylic acid) were without effect. Pretreatment with trypsin to remove the cytosolic inactivation domain largely occluded AA action. Intracellularly applied free synthetic β2-ball peptide induced inactivation of the hSlo-α current, and AA failed to enhance this current and slow the inactivation. These results suggest that AA removes inactivation by interacting, possibly through conformational changes, with β2 to prevent the inactivation ball from reaching its receptor. Our data reveal a novel mechanism of β-subunit–dependent modulation of BK channels by AA. In freshly dissociated mouse neocortical neurons, AA eliminated a transient component of whole cell K+ currents. BK channel inactivation may be a specific mechanism by which AA and other unsaturated fatty acids influence neuronal death/survival in neuropathological conditions.

scholarly journals Chronic Prenatal Hypoxia Down-Regulated BK Channel Β1 Subunits in Mesenteric Artery Smooth Muscle Cells of the Offspring

2018 ◽  
Vol 45 (4) ◽  
pp. 1603-1616 ◽  
Author(s):  
Bailin Liu ◽  
Yanping Liu ◽  
Ruixiu Shi ◽  
Xueqin Feng ◽  
Xiang Li ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Single Channel ◽  
Muscle Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
Mesenteric Arteries ◽  
Prenatal Hypoxia ◽  
Pregnant Rats ◽  
Α Subunit

Background/Aims: Chronic hypoxia in utero could impair vascular functions in the offspring, underlying mechanisms are unclear. This study investigated functional alteration in large-conductance Ca2+-activated K+ (BK) channels in offspring mesenteric arteries following prenatal hypoxia. Methods: Pregnant rats were exposed to normoxic control (21% O2, Con) or hypoxic (10.5% O2, Hy) conditions from gestational day 5 to 21, their 7-month-old adult male offspring were tested for blood pressure, vascular BK channel functions and expression using patch clamp and wire myograh technique, western blotting, and qRT-PCR. Results: Prenatal hypoxia increased pressor responses and vasoconstrictions to phenylephrine in the offspring. Whole-cell currents density of BK channels and amplitude of spontaneous transient outward currents (STOCs), not the frequency, were significantly reduced in Hy vascular myocytes. The sensitivity of BK channels to voltage, Ca2+, and tamoxifen were reduced in Hy myocytes, whereas the number of channels per patch and the single-channel conductance were unchanged. Prenatal hypoxia impaired NS1102- and tamoxifen-mediated relaxation in mesenteric arteries precontracted with phenylephrine in the presence of Nω-nitro-L-arginine methyl ester. The mRNA and protein expression of BK channel β1, not the α-subunit, was decreased in Hy mesenteric arteries. Conclusions: Impaired BK channel β1-subunits in vascular smooth muscle cells contributed to vascular dysfunction in the offspring exposed to prenatal hypoxia.

scholarly journals Detrusor overactivity is associated with downregulation of large-conductance calcium- and voltage-activated potassium channel protein

2010 ◽  
Vol 298 (6) ◽  
pp. F1416-F1423 ◽  
Author(s):  
Shaohua Chang ◽  
Cristiano Mendes Gomes ◽  
Joseph A. Hypolite ◽  
James Marx ◽  
Jaber Alanzi ◽  
...  
Keyword(s):  
Detrusor Overactivity ◽  
Bladder Outlet Obstruction ◽  
Rabbit Model ◽  
Outlet Obstruction ◽  
Bk Channels ◽  
Bk Channel ◽  
Β Subunit ◽  
Α Subunit ◽  
Translational Study ◽  
Channel Expression

Large-conductance voltage- and calcium-activated potassium (BK) channels have been shown to play a role in detrusor overactivity (DO). The goal of this study was to determine whether bladder outlet obstruction-induced DO is associated with downregulation of BK channels and whether BK channels affect myosin light chain 20 (MLC20) phosphorylation in detrusor smooth muscle (DSM). Partial bladder outlet obstruction (PBOO) was surgically induced in male New Zealand White rabbits. The rabbit PBOO model shows decreased voided volumes and increased voiding frequency. DSM from PBOO rabbits also show enhanced spontaneous contractions compared with control. Both BK channel α- and β-subunits were significantly decreased in DSM from PBOO rabbits. Immunostaining shows BKβ mainly expressed in DSM, and its expression is much less in PBOO DSM compared with control DSM. Furthermore, a translational study was performed to see whether the finding discovered in the animal model can be translated to human patients. The urodynamic study demonstrates several overactive DSM contractions during the urine-filling stage in benign prostatic hyperplasia (BPH) patients with DO, while DSM is very quiet in BPH patients without DO. DSM biopsies revealed significantly less BK channel expression at both mRNA and protein levels. The degree of downregulation of the BK β-subunit was greater than that of the BK α-subunit, and the downregulation of BK was only associated with DO, not BPH. Finally, the small interference (si) RNA-mediated downregulation of the BK β-subunit was employed to study the effect of BK depletion on MLC20 phosphorylation. siRNA-mediated BK channel reduction was associated with an increased MLC20 phosphorylation level in cultured DSM cells. In summary, PBOO-induced DO is associated with downregulation of BK channel expression in the rabbit model, and this finding can be translated to human BPH patients with DO. Furthermore, downregulation of the BK channel may contribute to DO by increasing the basal level of MLC20 phosphorylation.

scholarly journals Species-specific Differences among KCNMB3 BK β3 Auxiliary Subunits: Some β3 N-terminal Variants May Be Primate-specific Subunits

2008 ◽  
Vol 132 (1) ◽  
pp. 115-129 ◽  
Author(s):  
Xuhui Zeng ◽  
Xiao-Ming Xia ◽  
Christopher J. Lingle
Keyword(s):  
Functional Properties ◽  
Splice Variants ◽  
Mammalian Species ◽  
Amino Acid Identity ◽  
Bk Channel ◽  
Cdna Libraries ◽  
Auxiliary Subunits ◽  
Mouse Cdna ◽  
N Terminus ◽  
Species Specific

The KCNMB3 gene encodes one of a family of four auxiliary β subunits found in the mammalian genome that associate with Slo1 α subunits and regulate BK channel function. In humans, the KCNMB3 gene contains four N-terminal alternative exons that produce four functionally distinct β3 subunits, β3a–d. Three variants, β3a–c, exhibit kinetically distinct inactivation behaviors. Since investigation of the physiological roles of BK auxiliary subunits will depend on studies in rodents, here we have determined the identity and functional properties of mouse β3 variants. Whereas β1, β2, and β4 subunits exhibit 83.2%, 95.3%, and 93.8% identity between mouse and human, the mouse β3 subunit, excluding N-terminal splice variants, shares only 62.8% amino acid identity with its human counterpart. Based on an examination of the mouse genome and screening of mouse cDNA libraries, here we have identified only two N-terminal candidates, β3a and β3b, of the four found in humans. Both human and mouse β3a subunits produce a characteristic use-dependent inactivation. Surprisingly, whereas the hβ3b exhibits rapid inactivation, the putative mβ3b does not inactivate. Furthermore, unlike hβ3, the mβ3 subunit, irrespective of the N terminus, mediates a shift in gating to more negative potentials at a given Ca2+ concentration. The shift in gating gradually is lost following patch excision, suggesting that the gating shift involves some regulatory process dependent on the cytosolic milieu. Examination of additional genomes to assess conservation among splice variants suggests that the putative mβ3b N terminus may not be a true orthologue of the hβ3b N terminus and that both β3c and β3d appear likely to be primate-specific N-terminal variants. These results have three key implications: first, functional properties of homologous β3 subunits may differ among mammalian species; second, the specific physiological roles of homologous β3 subunits may differ among mammalian species; and, third, some β3 variants may be primate-specific ion channel subunits.

scholarly journals Position and Role of the BK Channel α Subunit S0 Helix Inferred from Disulfide Crosslinking

2008 ◽  
Vol 131 (6) ◽  
pp. 537-548 ◽  
Author(s):  
Guoxia Liu ◽  
Sergey I. Zakharov ◽  
Lin Yang ◽  
Shi-Xian Deng ◽  
Donald W. Landry ◽  
...  
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
Electrostatic Energy ◽  
Extracellular Loop ◽  
Membrane Domain ◽  
Α Subunit ◽  
Disulfide Crosslinking ◽  
Gating Charge ◽  
Sensor Activation

The position and role of the unique N-terminal transmembrane (TM) helix, S0, in large-conductance, voltage- and calcium-activated potassium (BK) channels are undetermined. From the extents of intra-subunit, endogenous disulfide bond formation between cysteines substituted for the residues just outside the membrane domain, we infer that the extracellular flank of S0 is surrounded on three sides by the extracellular flanks of TM helices S1 and S2 and the four-residue extracellular loop between S3 and S4. Eight different double cysteine–substituted alphas, each with one cysteine in the S0 flank and one in the S3–S4 loop, were at least 90% disulfide cross-linked. Two of these alphas formed channels in which 90% cross-linking had no effect on the V50 or on the activation and deactivation rate constants. This implies that the extracellular ends of S0, S3, and S4 are close in the resting state and move in concert during voltage sensor activation. The association of S0 with the gating charge bearing S3 and S4 could contribute to the considerably larger electrostatic energy required to activate the BK channel compared with typical voltage-gated potassium channels with six TM helices.

scholarly journals BK Channels in Rat and Human Pulmonary Smooth Muscle Cells are BKα-β1 Functional Complexes Lacking the Oxygen-Sensitive Stress Axis Regulated Exon Insert

2016 ◽  
Vol 6 (4) ◽  
pp. 563-575 ◽  
Author(s):  
Neil D. Detweiler ◽  
Li Song ◽  
Samantha J. McClenahan ◽  
Rachel J. Versluis ◽  
Sujay V. Kharade ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Smooth Muscle Cells ◽  
Splice Variants ◽  
Muscle Cells ◽  
Bk Channels ◽  
Bk Channel ◽  
Stress Axis ◽  
Human Donor ◽  
Intracellular Ca ◽  
Oxygen Sensitive

A loss of K+ efflux in pulmonary arterial smooth muscle cells (PASMCs) contributes to abnormal vasoconstriction and PASMC proliferation during pulmonary hypertension (PH). Activation of high-conductance Ca2+-activated (BK) channels represents a therapeutic strategy to restore K+ efflux to the affected PASMCs. However, the properties of BK channels in PASMCs—including sensitivity to BK channel openers (BKCOs)—are poorly defined. The goal of this study was to compare the properties of BK channels between PASMCs of normoxic (N) and chronic hypoxic (CH) rats and then explore key findings in human PASMCs. Polymerase chain reaction results revealed that 94.3% of transcripts encoding BKα pore proteins in PASMCs from N rats represent splice variants lacking the stress axis regulated exon insert, which confers oxygen sensitivity. Subsequent patch-clamp recordings from inside-out (I-O) patches confirmed a dense population of BK channels insensitive to hypoxia. The BK channels were highly activated by intracellular Ca2+ and the BKCO lithocholate; these responses require BK α-β1 subunit coupling. PASMCs of CH rats with established PH exhibited a profound overabundance of the dominant oxygen-insensitive BKα variant. Importantly, human BK (hBK) channels in PASMCs from human donor lungs also represented the oxygen-insensitive BKα variant activated by BKCOs. The hBK channels showed significantly enhanced Ca2+ sensitivity compared with rat BK channels. We conclude that rat BK and hBK channels in PASMCs are oxygen-insensitive BK α-β1 complexes highly sensitive to Ca2+ and the BKCO lithocholate. BK channels are overexpressed in PASMCs of a rat model of PH and may provide an abundant target for BKCOs designed to restore K+ efflux.

scholarly journals Regulation of large conductance calcium- and voltage-activated potassium (BK) channels by S-palmitoylation

2013 ◽  
Vol 41 (1) ◽  
pp. 67-71 ◽  
Author(s):  
Michael J. Shipston
Keyword(s):  
Surface Expression ◽  
Bk Channels ◽  
Bk Channel ◽  
Post Translational Modification ◽  
Physiological Control ◽  
Α Subunit ◽  
Channel Trafficking ◽  
C Terminus ◽  
Family Protein ◽  
Health And Disease

BK (large conductance calcium- and voltage-activated potassium) channels are important determinants of physiological control in the nervous, endocrine and vascular systems with channel dysfunction associated with major disorders ranging from epilepsy to hypertension and obesity. Thus the mechanisms that control channel surface expression and/or activity are important determinants of their (patho)physiological function. BK channels are S-acylated (palmitoylated) at two distinct sites within the N- and C-terminus of the pore-forming α-subunit. Palmitoylation of the N-terminus controls channel trafficking and surface expression whereas palmitoylation of the C-terminal domain determines regulation of channel activity by AGC-family protein kinases. Recent studies are beginning to reveal mechanistic insights into how palmitoylation controls channel trafficking and cross-talk with phosphorylation-dependent signalling pathways. Intriguingly, each site of palmitoylation is regulated by distinct zDHHCs (palmitoyl acyltransferases) and APTs (acyl thioesterases). This supports that different mechanisms may control substrate specificity by zDHHCs and APTs even within the same target protein. As palmitoylation is dynamically regulated, this fundamental post-translational modification represents an important determinant of BK channel physiology in health and disease.

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

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

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

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