Cochlear Function in Mice Lacking the BK Channel α, β1, or β4 Subunits

Pyott, Sonja J.; Meredith, Andrea L.; Fodor, Anthony A.; Vázquez, Aitor; Yamoah, Ebenezer N.; Aldrich, Richard W.

doi:10.1074/jbc.m608726200

Cited by 96 publications

(82 citation statements)

References 63 publications

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“…In these vertebrates, BK is colocalized with L-type Ca 2ϩ channels in presynaptic active zones (3) and is thus coupled to neurotransmitter release as described for the nerve muscle synapse (4,5). Although the onset of this channel during cochlear development in both mammals and non-mammals coincides with an increase in hearing sensitivity (6,7), its function is less clear in the former where hair cells are not frequency-tuned and studies report either the presence or the absence of hearing with the loss of BK (8,9). The BK channel has been localized to both the outer hair cells (OHC) (10) and inner hair cells (IHC) (7,(11)(12)(13) in mammals.…”

Section: Bkmentioning

confidence: 99%

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A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

Kathiresan

Harvey

Orchard

et al. 2009

Molecular & Cellular Proteomics

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The large conductance Ca 2؉ -activated K ؉ or BK channel has a role in sensory/neuronal excitation, intracellular signaling, and metabolism. In the non-mammalian cochlea, the onset of BK during development correlates with increased hearing sensitivity and underlies frequency tuning in non-mammals, whereas its role is less clear in mammalian hearing. To gain insights into BK function in mammals, coimmunoprecipitation and two-dimensional PAGE, combined with mass spectrometry, were used to reveal 174 putative BKAPs from cytoplasmic and membrane/cytoskeletal fractions of mouse cochlea. Eleven BKAPs were verified using reciprocal coimmunoprecipitation, including annexin, apolipoprotein, calmodulin, hippocalcin, and myelin P0, among others. These proteins were immunocolocalized with BK in sensory and neuronal cells. A bioinformatics approach was used to mine databases to reveal binary partners and the resultant protein network, as well as to determine previous ion channel affiliations, subcellular localization, and cellular processes. The search for binary partners using the IntAct molecular interaction database produced a putative global network of 160 nodes connected with 188 edges that contained 12 major hubs. Additional mining of databases revealed that more than 50% of primary BKAPs had prior affiliations with K ؉ and Ca 2؉ channels. Although a majority of BKAPs are found in either the cytoplasm or membrane and contribute to cellular processes that primarily involve metabolism (30.5%) and trafficking/scaffolding (23.6%), at least 20% are mitochondrial-related. Among the BKAPs are chaperonins such as calreticulin, GRP78, and HSP60 that, when reduced with siRNAs, alter BK␣ expression in CHO cells. Studies of BK␣ in mitochondria revealed compartmentalization in sensory cells, whereas heterologous expression of a BK-DEC splice variant cloned from cochlea revealed a BK mitochondrial candidate. The studies described herein provide insights into BK-related functions that include not only cell excitation, but also cell signaling and apoptosis, and involve proteins concerned with Ca 2؉ regulation, structure, and hearing loss. BK 1 channels act as sensors for membrane voltage and intracellular Ca 2ϩ , thereby linking cell excitability, metabolism, and signaling. BK channels, also known as Slo, are large conductance channels (100 -300 pS) (1) composed of four ␣-subunits that are regulated by four auxiliary ␤-subunits. The ␣-subunit of the BK channel has six to seven transmembranespanning regions (S0 -S6) where the S0 domain places the N terminus extracellularly as a binding site for the beta subunit. The transmembrane domains S1-S4 are responsible for sensing voltage changes, whereas the pore forming region, between S5-S6, conducts ions. BK has a large C-terminal region that contains target sequences for channel modulation such as a Ca 2ϩ bowl, two domains that regulate the conductance of K ϩ (RCK1 and RCK2), a tetramerization domain, leucine zipper motifs, a hemebinding motif, two phosphorylation sites, and a caveolin-targ...

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Section: Bkmentioning

confidence: 99%

“…The BK channel has been localized to both the outer hair cells (OHC) (10) and inner hair cells (IHC) (7,(11)(12)(13) in mammals. However, unlike non-mammals, the BK channel appears in both synaptic and extrasynaptic sites near the apical end or neck of the IHC (9).…”

Section: Bkmentioning

confidence: 99%

A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

Kathiresan

Harvey

Orchard

et al. 2009

Molecular & Cellular Proteomics

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“…BK channel proteins are homotetramers formed by BK α-subunits, which then associate with different β-or γ-subunits in a tissue-specific manner (13)(14)(15)(16)(17)(18)(19)(20)(21)(22). The α-subunit of the BK (K Ca 1.1) channel is encoded by the KCNMA1 gene, first discovered in Drosophila as the slowpoke mutation (dSlo) (23, 24), and later identified in mouse (mSlo1) and human (hSlo1) (25, 26).…”

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confidence: 99%

BK channel opening involves side-chain reorientation of multiple deep-pore residues

Chen

Yan

Aldrich

2013

Proc. Natl. Acad. Sci. U.S.A.

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Three deep-pore locations, L312, A313, and A316, were identified in a scanning mutagenesis study of the BK (Ca 2+ -activated, largeconductance K + ) channel S6 pore, where single aspartate substitutions led to constitutively open mutant channels (L312D, A313D, and A316D). To understand the mechanisms of the constitutive openness of these mutant channels, we individually mutated these three sites into the other 18 amino acids. We found that charged or polar side-chain substitutions at each of the sites resulted in constitutively open mutant BK channels, with high open probability at negative voltages, as well as a loss of voltage and Ca 2+ dependence. Given the fact that multiple pore residues in BK displayed side-chain hydrophilicity-dependent constitutive openness, we propose that BK channel opening involves structural rearrangement of the deep-pore region, where multiple residues undergo conformational changes that may increase the exposure of their side chains to the polar environment of the pore.2+ -activated K + (BK) channels regulate physiological processes such as neurotransmitter release, smooth muscle contraction, and hair cell frequency tuning (1-12). BK channel proteins are homotetramers formed by BK α-subunits, which then associate with different β-or γ-subunits in a tissue-specific manner (13)(14)(15)(16)(17)(18)(19)(20)(21)(22). The α-subunit of the BK (K Ca 1.1) channel is encoded by the KCNMA1 gene, first discovered in Drosophila as the slowpoke mutation (dSlo) (23, 24), and later identified in mouse (mSlo1) and human (hSlo1) (25, 26). Each α-subunit has seven transmembrane segments (S0-S6), with the S6 segments lining the pore. A similar structural arrangement is found in other members of the K + channel protein family. From a functional point of view, the gating behavior of BK channels can be described as a central C⇔O (i.e., closed⇔open) transition, influenced by voltage sensor movement and/or Ca 2+ binding (27-31). The structural basis for this C⇔O transition is believed to be conformational changes of the S6 segment and/or the selectivity filter (32, 33), controlling the passage of K + ions across the membrane.Molecular details of gating-related conformational changes have been probed with mutagenesis-based methods for BK and related channels. Although it has been demonstrated that voltage-gated (Kv) K + channels open by a cytoplasmic S6 "bundle crossing" gate (34-37), evidence has accumulated that the opening conformational change of BK, like cyclic nucleotidegated (CNG) channels, occurs deeper in the pore, closer to the selectivity filter (38)(39)(40)(41)(42)(43)(44)(45)(46). With the goal of further understanding the opening conformational change in BK channels, we used a histidine substitution/protonation strategy and identified a residue in BK S6 (M314 in hSlo1) whose side chain turns more toward the pore when the channel is open. The open conformation can be stabilized by the presence of side-chain charges at this location, with the aspartate mutant being the most effective in keeping...

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“…Taken together, these results demonstrate that the secretion of K ϩ requires and is likely mediated by KCa1.1 potassium channels localized to the apical membranes of striated and excretory duct cells in the mouse submandibular exocrine gland. salivary gland; potassium secretion; calcium-activated K channels; duct cells MAXI-K CHANNELS ARE ASSOCIATED with a diverse array of cellular functions including, for example, smooth muscle contractility (22,37), cell volume control (32,42), neuronal action potentials (26,27,39), hearing loss in cochlear hair cells (31,34), and K ϩ secretion by the renal tubules and the crypt cells of the distal colon (29,38). We have previously demonstrated that the K Ca 1.1 gene (also known as Kcnma1) encodes the maxi-K channel in the acinar cells of parotid and submandibular exocrine glands (32,33).…”

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confidence: 99%

Apical maxi-K (K_Ca1.1) channels mediate K⁺ secretion by the mouse submandibular exocrine gland

Nakamoto¹,

Romanenko²,

Takahashi³

et al. 2008

American Journal of Physiology-Cell Physiology

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The exocrine salivary glands of mammals secrete K+ by an unknown pathway that has been associated with HCO3− efflux. However, the present studies found that K+ secretion in the mouse submandibular gland did not require HCO3−, demonstrating that neither K+/HCO3− cotransport nor K+/H+ exchange mechanisms were involved. Because HCO3− did not appear to participate in this process, we tested whether a K channel is required. Indeed, K+ secretion was inhibited >75% in mice with a null mutation in the maxi-K, Ca2+-activated K channel (KCa1.1) but was unchanged in mice lacking the intermediate-conductance IKCa1 channel (KCa3.1). Moreover, paxilline, a specific maxi-K channel blocker, dramatically reduced the K+ concentration in submandibular saliva. The K+ concentration of saliva is well known to be flow rate dependent, the K+ concentration increasing as the flow decreases. The flow rate dependence of K+ secretion was nearly eliminated in K Ca 1.1 null mice, suggesting an important role for KCa1.1 channels in this process as well. Importantly, a maxi-K-like current had not been previously detected in duct cells, the theoretical site of K+ secretion, but we found that KCa1.1 channels localized to the apical membranes of both striated and excretory duct cells, but not granular duct cells, using immunohistochemistry. Consistent with this latter observation, maxi-K currents were not detected in granular duct cells. Taken together, these results demonstrate that the secretion of K+ requires and is likely mediated by KCa1.1 potassium channels localized to the apical membranes of striated and excretory duct cells in the mouse submandibular exocrine gland.

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Cochlear Function in Mice Lacking the BK Channel α, β1, or β4 Subunits

Cited by 96 publications

References 63 publications

A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

BK channel opening involves side-chain reorientation of multiple deep-pore residues

Apical maxi-K (K_Ca1.1) channels mediate K⁺ secretion by the mouse submandibular exocrine gland

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Cochlear Function in Mice Lacking the BK Channel α, β1, or β4 Subunits

Cited by 96 publications

References 63 publications

A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

A Protein Interaction Network for the Large Conductance Ca2+-activated K+ Channel in the Mouse Cochlea

BK channel opening involves side-chain reorientation of multiple deep-pore residues

Apical maxi-K (KCa1.1) channels mediate K+ secretion by the mouse submandibular exocrine gland

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Apical maxi-K (K_Ca1.1) channels mediate K⁺ secretion by the mouse submandibular exocrine gland