scholarly journals Two distinct effects of PIP2 underlie auxiliary subunit-dependent modulation of Slo1 BK channels

2015 ◽  
Vol 145 (4) ◽  
pp. 331-343 ◽  
Author(s):  
Yutao Tian ◽  
Florian Ullrich ◽  
Rong Xu ◽  
Stefan H. Heinemann ◽  
Shangwei Hou ◽  
...  
Keyword(s):  
Divalent Cation ◽  
Critical Role ◽  
Cell Types ◽  
Bk Channels ◽  
Bk Channel ◽  
Positive Direction ◽  
Human Embryonic Kidney Cells ◽  
Auxiliary Subunits ◽  
Voltage Dependent ◽  
Negative Surface

Phosphatidylinositol 4,5-bisphosphate (PIP2) plays a critical role in modulating the function of numerous ion channels, including large-conductance Ca2+- and voltage-dependent K+ (BK, Slo1) channels. Slo1 BK channel complexes include four pore-forming Slo1 (α) subunits as well as various regulatory auxiliary subunits (β and γ) that are expressed in different tissues. We examined the molecular and biophysical mechanisms underlying the effects of brain-derived PIP2 on human Slo1 BK channel complexes with different subunit compositions that were heterologously expressed in human embryonic kidney cells. PIP2 inhibited macroscopic currents through Slo1 channels without auxiliary subunits and through Slo1 + γ1 complexes. In contrast, PIP2 markedly increased macroscopic currents through Slo1 + β1 and Slo1 + β4 channel complexes and failed to alter macroscopic currents through Slo1 + β2 and Slo1 + β2 Δ2–19 channel complexes. Results obtained at various membrane potentials and divalent cation concentrations suggest that PIP2 promotes opening of the ion conduction gate in all channel types, regardless of the specific subunit composition. However, in the absence of β subunits positioned near the voltage-sensor domains (VSDs), as in Slo1 and probably Slo1 + γ1, PIP2 augments the negative surface charge on the cytoplasmic side of the membrane, thereby shifting the voltage dependence of VSD-mediated activation in the positive direction. When β1 or β4 subunits occupy the space surrounding the VSDs, only the stimulatory effect of PIP2 is evident. The subunit compositions of native Slo1 BK channels differ in various cell types; thus, PIP2 may exert distinct tissue- and divalent cation–dependent modulatory influences.

BK channel β1-subunit regulation of calcium handling and constriction in tracheal smooth muscle

2006 ◽  
Vol 291 (4) ◽  
pp. L802-L810 ◽  
Author(s):  
Iurii Semenov ◽  
Bin Wang ◽  
Jeremiah T. Herlihy ◽  
Robert Brenner
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Cell Types ◽  
Bk Channels ◽  
Bk Channel ◽  
Tracheal Smooth Muscle ◽  
Calcium Handling ◽  
Cholinergic Signaling ◽  
Smooth Muscle Function ◽  
Voltage Dependent

The large-conductance, Ca2+-activated K+ (BK) channels are regulators of voltage-dependent Ca2+ entry in many cell types. The BK channel accessory β1-subunit promotes channel activation in smooth muscle and is required for proper tone in the vasculature and bladder. However, although BK channels have also been implicated in airway smooth muscle function, their regulation by the β1-subunit has not been investigated. Utilizing the gene-targeted mice for the β1-subunit gene, we have investigated the role of the β1-subunit in tracheal smooth muscle. In mice with the β1-subunit-knockout allele, BK channel activity was significantly reduced in excised tracheal smooth muscle patches and spontaneous BK currents were reduced in whole tracheal smooth muscle cells. Knockout of the β1-subunit resulted in an increase in resting Ca2+ levels and an increase in the sustained component of Ca2+ influx after cholinergic signaling. Tracheal constriction studies demonstrate that the level of constriction is the same with knockout of the β1-subunit and BK channel block with paxillin, indicating that BK channels contribute little to airway relaxation in the absence of the β1-subunit. Utilizing nifedipine, we found that the increased constriction caused by knockout of the β1-subunit could be accounted for by an increased recruitment of L-type voltage-dependent Ca2+ channels. These results indicate that the β1-subunit is required in airway smooth muscle for control of voltage-dependent Ca2+ influx during rest and after cholinergic signaling in BK channels.

scholarly journals The liverwort Marchantia polymorpha operates a depolarization-activated Slowpoke (SLO) K+ channel that recognises pH changes in the environment

2021 ◽  
Author(s):  
Frances C. Sussmilch ◽  
Jennifer Boehm ◽  
Guido Gessner ◽  
Tobias Maierhofer ◽  
Thomas D. Mueller ◽  
...  
Keyword(s):  
Critical Role ◽  
Bk Channels ◽  
Bk Channel ◽  
K Channel ◽  
Marchantia Polymorpha ◽  
Terrestrial Environment ◽  
Ph Changes ◽  
Kv Channels ◽  
Voltage Dependent ◽  
Genes Encoding

Voltage-dependent ion channels are a prerequisite for cellular excitability and electrical communication - important traits for multicellular organisms to thrive in a changeable terrestrial environment. Based on their presence in extant embryophytes and closely-related green algae, the first plants to survive on land likely possessed genes encoding channels with homology to large-conductance calcium-activated K+ channels (BK channels from the Slo family) in addition to primary voltage-gated potassium channels from the plant VG-type family (Shaker or Kv channels). While the function and gating of Shaker channels has been characterised in flowering plants, so far knowledge of BK channels has been limited to animal models. In humans, BK-mediated K+ efflux has a critical role in sperm motility and membrane polarisation to enable fertilisation. In the liverwort Marchantia polymorpha, the MpBK2a channel gene is most highly expressed in male reproductive tissue, suggesting that these channels may function in sexual reproduction. We characterised MpBK2a channels and found them to be strongly K+-selective, outward-rectifying, 80-pS channels capable of repolarising the membrane after stimulus-dependent depolarisation. In contrast to its animal counterpart, MpBK2a is insensitive to cytoplasmic Ca2+ variations but effectively gated by pH changes. Given that this plant BK channel is active even in the presence of trace amounts of external K+ and at low pH, the liverwort channel could have stabilised the membrane potential under stressful pre-historic conditions including nutrient-depleted and acid environments as early plant pioneers conquered land.

scholarly journals BK channel inhibition by strong extracellular acidification

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Yu Zhou ◽  
Xiao-Ming Xia ◽  
Christopher J Lingle
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
Extracellular Acidification ◽  
Channel Inhibition ◽  
Wide Range ◽  
The Family ◽  
Voltage Dependent ◽  
Intracellular Organelles ◽  
Extracellular Side ◽  
Key Residues

Mammalian BK-type voltage- and Ca2+-dependent K+ channels are found in a wide range of cells and intracellular organelles. Among different loci, the composition of the extracellular microenvironment, including pH, may differ substantially. For example, it has been reported that BK channels are expressed in lysosomes with their extracellular side facing the strongly acidified lysosomal lumen (pH ~4.5). Here we show that BK activation is strongly and reversibly inhibited by extracellular H+, with its conductance-voltage relationship shifted by more than +100 mV at pHO 4. Our results reveal that this inhibition is mainly caused by H+ inhibition of BK voltage-sensor (VSD) activation through three acidic residues on the extracellular side of BK VSD. Given that these key residues (D133, D147, D153) are highly conserved among members in the voltage-dependent cation channel superfamily, the mechanism underlying BK inhibition by extracellular acidification might also be applicable to other members in the family.

scholarly journals LRRC52 regulates BK channel function and localization in mouse cochlear inner hair cells

2019 ◽  
Vol 116 (37) ◽  
pp. 18397-18403 ◽  
Author(s):  
Christopher J. Lingle ◽  
Pedro L. Martinez-Espinosa ◽  
Aizhen Yang-Hood ◽  
Luis E. Boero ◽  
Shelby Payne ◽  
...  
Keyword(s):  
Hair Cells ◽  
Glutamate Release ◽  
Nerve Fibers ◽  
Bk Channels ◽  
Bk Channel ◽  
Membrane Potentials ◽  
Macromolecular Complex ◽  
Inner Hair Cells ◽  
Channel Function ◽  
Voltage Dependent

The perception of sound relies on sensory hair cells in the cochlea that convert the mechanical energy of sound into release of glutamate onto postsynaptic auditory nerve fibers. The hair cell receptor potential regulates the strength of synaptic transmission and is shaped by a variety of voltage-dependent conductances. Among these conductances, the Ca2+- and voltage-activated large conductance Ca2+-activated K+channel (BK) current is prominent, and in mammalian inner hair cells (IHCs) displays unusual properties. First, BK currents activate at unprecedentedly negative membrane potentials (−60 mV) even in the absence of intracellular Ca2+elevations. Second, BK channels are positioned in clusters away from the voltage-dependent Ca2+channels that mediate glutamate release from IHCs. Here, we test the contributions of two recently identified leucine-rich-repeat–containing (LRRC) regulatory γ subunits, LRRC26 and LRRC52, to BK channel function and localization in mouse IHCs. Whereas BK currents and channel localization were unaltered in IHCs fromLrrc26knockout (KO) mice, BK current activation was shifted more than +200 mV in IHCs fromLrrc52KO mice. Furthermore, the absence of LRRC52 disrupted BK channel localization in the IHCs. Given that heterologous coexpression of LRRC52 with BK α subunits shifts BK current gating about −90 mV, to account for the profound change in BK activation range caused by removal of LRRC52, we suggest that additional factors may help define the IHC BK gating range. LRRC52, through stabilization of a macromolecular complex, may help retain some other components essential both for activation of BK currents at negative membrane potentials and for appropriate BK channel positioning.

scholarly journals Heme Regulates Allosteric Activation of the Slo1 BK Channel

2005 ◽  
Vol 126 (1) ◽  
pp. 7-21 ◽  
Author(s):  
Frank T. Horrigan ◽  
Stefan H. Heinemann ◽  
Toshinori Hoshi
Keyword(s):  
Divalent Cations ◽  
Ionic Currents ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Gating Currents ◽  
Calcium Dependent ◽  
Channel Opening ◽  
Activation Gate ◽  
Voltage Dependent

Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531–535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G–V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G–V simulated by weakening the coupling of both Ca2+ binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca2+- and voltage-dependent gating as well as intrinsic stability of the open state.

scholarly journals The BK channel gating ring is strongly coupled to the voltage sensor

2018 ◽  
Author(s):  
Pablo Miranda ◽  
Miguel Holmgren ◽  
Teresa Giraldez
Keyword(s):  
Conformational Changes ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Voltage Sensitivity ◽  
Divalent Ions ◽  
Gating Currents ◽  
Open Probability ◽  
Voltage Dependent ◽  
Tightly Coupled

ABSTRACTThe open probability of large conductance voltage- and calcium-dependent potassium (BK) channels is regulated allosterically by changes in the transmembrane voltage and intracellular concentration of divalent ions (Ca2+ and Mg2+). The divalent cation sensors reside within the gating ring formed by eight Regulator of Conductance of Potassium (RCK) domains, two from each of the four channel subunits. Overall, the gating ring contains 12 sites that can bind Ca2+ with different affinities. Using patch-clamp fluorometry, we have shown robust changes in FRET signals within the gating ring in response to divalent ions and voltage, which do not directly track open probability. Only the conformational changes triggered through the RCK1 binding site are voltage-dependent in presence of Ca2+. Because the gating ring is outside the electric field, it must gain voltage sensitivity from coupling to the voltage-dependent channel opening, the voltage sensor or both. Here we demonstrate that alterations of voltage sensor dynamics known to shift gating currents produce a cognate shift in the gating ring voltage dependence, whereas changing BK channels’ relative probability of opening had little effect. These results strongly suggest that the conformational changes of the RCK1 domain of the gating ring are tightly coupled to the voltage sensor function, and this interaction is central to the allosteric modulation of BK channels.

Abstract 376: Nedd4 Regulated Bk Channels in Diabetes Mellitus

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
DAI-MIN ZHANG ◽  
Shao-liang Chen ◽  
Yanrong Zhu ◽  
Peng Ye
Keyword(s):  
Diabetes Mellitus ◽  
Current Density ◽  
Knockout Mice ◽  
Vascular Function ◽  
Critical Role ◽  
Vascular Diseases ◽  
Bk Channels ◽  
Bk Channel ◽  
Hek293 Cells ◽  
Kinetic Properties

Big conductance calcium activated potassium(BK) channel plays a critical role in pathophysiological regulation of vascular function. Recent studies indicated that the expression reduction of BK channels in high glucose condition exacerbated vessel dilation, and led to coronary artery diseases, while BK channel expression was reserved in A-kinase anchoring protein(AKAP) knockout mice at same condition. Here, We are to investigate heterologous co-expression of Nedd4 ligase, ubiquitin protein ligase, and KCa1.1 in HEK293 cells. The result shown that co-expression reduced BK current density without modulation of kinetic properties as measured by path clamp techniques. Modulation of current density was dependent on ligase activity and was lost in AKAP knockout mice with diabetes mellitus. Taken together, our data disclose a novel mechanism of KCa1.1 channel regulation that NEDD4 decreased BK channels expression in diabetes mellitus depending on AKAP signal complexity. These findings provide a new insight into potential therapeutic target in vascular diseases, especially in diabetes mellitus.This work was supported by the National Natural Science Foundation of China(Grant No. 8137034)

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

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

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

scholarly journals An unexpected journey: conceptual evolution of mechanoregulated potassium transport in the distal nephron

2016 ◽  
Vol 310 (4) ◽  
pp. C243-C259 ◽  
Author(s):  
Rolando Carrisoza-Gaytan ◽  
Marcelo D. Carattino ◽  
Thomas R. Kleyman ◽  
Lisa M. Satlin
Keyword(s):  
Flow Rate ◽  
Fluid Shear Stress ◽  
Collecting Duct ◽  
Critical Role ◽  
Bk Channels ◽  
Bk Channel ◽  
Macromolecular Complex ◽  
Urinary Flow ◽  
Cortical Collecting Duct ◽  
Distal Nephron

Flow-induced K secretion (FIKS) in the aldosterone-sensitive distal nephron (ASDN) is mediated by large-conductance, Ca2+/stretch-activated BK channels composed of pore-forming α-subunits (BKα) and accessory β-subunits. This channel also plays a critical role in the renal adaptation to dietary K loading. Within the ASDN, the cortical collecting duct (CCD) is a major site for the final renal regulation of K homeostasis. Principal cells in the ASDN possess a single apical cilium whereas the surfaces of adjacent intercalated cells, devoid of cilia, are decorated with abundant microvilli and microplicae. Increases in tubular (urinary) flow rate, induced by volume expansion, diuretics, or a high K diet, subject CCD cells to hydrodynamic forces (fluid shear stress, circumferential stretch, and drag/torque on apical cilia and presumably microvilli/microplicae) that are transduced into increases in principal (PC) and intercalated (IC) cell cytoplasmic Ca2+ concentration that activate apical voltage-, stretch- and Ca2+-activated BK channels, which mediate FIKS. This review summarizes studies by ourselves and others that have led to the evolving picture that the BK channel is localized in a macromolecular complex at the apical membrane, composed of mechanosensitive apical Ca2+ channels and a variety of kinases/phosphatases as well as other signaling molecules anchored to the cytoskeleton, and that an increase in tubular fluid flow rate leads to IC- and PC-specific responses determined, in large part, by the cell-specific composition of the BK channels.

scholarly journals Cadmium–cysteine coordination in the BK inner pore region and its structural and functional implications

2015 ◽  
Vol 112 (16) ◽  
pp. 5237-5242 ◽  
Author(s):  
Yu Zhou ◽  
Xiao-Ming Xia ◽  
Christopher J. Lingle
Keyword(s):  
Conformational Changes ◽  
State Dependence ◽  
Bk Channels ◽  
Bk Channel ◽  
Pore Region ◽  
Kv Channel ◽  
Kv Channels ◽  
Voltage Dependent ◽  
Channel Structures ◽  
Inner Pore

To probe structure and gating-associated conformational changes in BK-type potassium (BK) channels, we examined consequences of Cd2+ coordination with cysteines introduced at two positions in the BK inner pore. At V319C, the equivalent of valine in the conserved Kv proline-valine-proline (PVP) motif, Cd2+ forms intrasubunit coordination with a native glutamate E321, which would place the side chains of V319C and E321 much closer together than observed in voltage-dependent K+ (Kv) channel structures, requiring that the proline between V319C and E321 introduces a kink in the BK S6 inner helix sharper than that observed in Kv channel structures. At inner pore position A316C, Cd2+ binds with modest state dependence, suggesting the absence of an ion permeation gate at the cytosolic side of BK channel. These results highlight fundamental structural differences between BK and Kv channels in their inner pore region, which likely underlie differences in voltage-dependent gating between these channels.

Sign in / Sign up

Export Citation Format

Share Document