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Quantal Ca 2+ release mediated by very few IP 3 receptors that rapidly inactivate allows graded responses to IP 3. Cell Rep 2021; 37:109932. [PMID: 34731613 PMCID: PMC8578705 DOI: 10.1016/j.celrep.2021.109932] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 07/16/2021] [Accepted: 10/12/2021] [Indexed: 11/22/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3Rs) are intracellular Ca2+ channels that link extracellular stimuli to Ca2+ signals. Ca2+ release from intracellular stores is "quantal": low IP3 concentrations rapidly release a fraction of the stores. Ca2+ release then slows or terminates without compromising responses to further IP3 additions. The mechanisms are unresolved. Here, we synthesize a high-affinity partial agonist of IP3Rs and use it to demonstrate that quantal responses do not require heterogenous Ca2+ stores. IP3Rs respond incrementally to IP3 and close after the initial response to low IP3 concentrations. Comparing functional responses with IP3 binding shows that only a tiny fraction of a cell's IP3Rs mediate incremental Ca2+ release; inactivation does not therefore affect most IP3Rs. We conclude, and test by simulations, that Ca2+ signals evoked by IP3 pulses arise from rapid activation and then inactivation of very few IP3Rs. This allows IP3Rs to behave as increment detectors mediating graded Ca2+ release.
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Takeshima H, Venturi E, Sitsapesan R. New and notable ion-channels in the sarcoplasmic/endoplasmic reticulum: do they support the process of intracellular Ca²⁺ release? J Physiol 2014; 593:3241-51. [PMID: 26228553 DOI: 10.1113/jphysiol.2014.281881] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Accepted: 10/10/2014] [Indexed: 12/11/2022] Open
Abstract
Intracellular Ca(2+) release through ryanodine receptor (RyR) and inositol trisphosphate receptor (IP3 R) channels is supported by a complex network of additional proteins that are located in or near the Ca(2+) release sites. In this review, we focus, not on RyR/IP3 R, but on other ion-channels that are known to be present in the sarcoplasmic/endoplasmic reticulum (ER/SR) membranes. We review their putative physiological roles and the evidence suggesting that they may support the process of intracellular Ca(2+) release, either indirectly by manipulating ionic fluxes across the ER/SR membrane or by directly interacting with a Ca(2+) -release channel. These channels rarely receive scientific attention because of the general lack of information regarding their biochemical and/or electrophysiological characteristics makes it difficult to predict their physiological roles and their impact on SR Ca(2+) fluxes. We discuss the possible role of SR K(+) channels and, in parallel, detail the known biochemical and biophysical properties of the trimeric intracellular cation (TRIC) proteins and their possible biological and pathophysiological roles in ER/SR Ca(2+) release. We summarise what is known regarding Cl(-) channels in the ER/SR and the non-selective cation channels or putative 'Ca(2+) leak channels', including mitsugumin23 (MG23), pannexins, presenilins and the transient receptor potential (TRP) channels that are distributed across ER/SR membranes but which have not yet been fully characterised functionally.
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Affiliation(s)
- Hiroshi Takeshima
- Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto, 606-8501, Japan
| | - Elisa Venturi
- Department of Pharmacology, University of Oxford, Oxford OX1 3QT, UK
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3
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Fedorenko OA, Marchenko SM. Ion channels of the nuclear membrane of hippocampal neurons. Hippocampus 2014; 24:869-76. [PMID: 24710998 DOI: 10.1002/hipo.22276] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/31/2014] [Indexed: 11/09/2022]
Abstract
Rise in Ca(2+) concentration in the nucleus affects gene transcription and has been implicated in neuroprotection, transcription-dependent neuronal plasticity, and pain modulation, but the mechanism of regulation of nuclear Ca(2+) remains poorly understood. The nuclear envelope is a part of the endoplasmic reticulum and may be one of the sources of nuclear Ca(2+) . Here, we studied ion channels in the nuclear membrane of hippocampal neurons using the patch-clamp technique. We have found that the nuclear membrane of CA1 pyramidal and dentate gyrus granule (DG), but not CA3 pyramidal neurons, was enriched in functional inositol 1,4,5-trisphosphate receptors/Ca(2+) -release channels (IP3 Rs) localized mainly in the inner nuclear membrane. A single nuclear ryanodine receptor (RyR) has been detected only in DG granule neurons. Nuclei of the hippocampal neurons also expressed a variety of spontaneously active cation and anion channels specific for each type of neuron. In particular, large-conductance ion channels selective for monovalent cations (LCC) were coexpressed with IP3 Rs. These data suggest that: (1) the nuclear membranes of hippocampal neurons contain distinct sets of ion channels, which are specific for each type of neuron; (2) IP3 Rs, but not RyRs are targeted to the inner nuclear membrane of CA1 pyramidal and DG granule, but they were not found in the nuclear membranes of CA3 pyramidal neurons; (3) the nuclear envelope of these neurons is specialized to release Ca(2+) into the nucleoplasm which may amplify Ca(2+) signals entering the nucleus from the cytoplasm or generate Ca(2+) transients on its own; (4) LCC channels are an integral part the of Ca(2+) -releasing machinery providing a route for counterflow of К(+) and thereby facilitating Ca(2+) movement in and out of the Ca(2+) store.
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Affiliation(s)
- Olena A Fedorenko
- Bogomoletz Institute of Physiology, Department of Brain Physiology, 4 Bogomoletz Street, Kiev, 01024, Ukraine; State Key Laboratory of Molecular and Cellular Biology, 4 Bogomoletz Street, Kiev, 01024, Ukraine
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Bi D, Toyama K, Lemaître V, Takai J, Fan F, Jenkins DP, Wulff H, Gutterman DD, Park F, Miura H. The intermediate conductance calcium-activated potassium channel KCa3.1 regulates vascular smooth muscle cell proliferation via controlling calcium-dependent signaling. J Biol Chem 2013; 288:15843-53. [PMID: 23609438 PMCID: PMC3668741 DOI: 10.1074/jbc.m112.427187] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2012] [Revised: 04/12/2013] [Indexed: 01/14/2023] Open
Abstract
The intermediate conductance calcium-activated potassium channel KCa3.1 contributes to a variety of cell activation processes in pathologies such as inflammation, carcinogenesis, and vascular remodeling. We examined the electrophysiological and transcriptional mechanisms by which KCa3.1 regulates vascular smooth muscle cell (VSMC) proliferation. Platelet-derived growth factor-BB (PDGF)-induced proliferation of human coronary artery VSMCs was attenuated by lowering intracellular Ca(2+) concentration ([Ca(2+)]i) and was enhanced by elevating [Ca(2+)]i. KCa3.1 blockade or knockdown inhibited proliferation by suppressing the rise in [Ca(2+)]i and attenuating the expression of phosphorylated cAMP-response element-binding protein (CREB), c-Fos, and neuron-derived orphan receptor-1 (NOR-1). This antiproliferative effect was abolished by elevating [Ca(2+)]i. KCa3.1 overexpression induced VSMC proliferation, and potentiated PDGF-induced proliferation, by inducing CREB phosphorylation, c-Fos, and NOR-1. Pharmacological stimulation of KCa3.1 unexpectedly suppressed proliferation by abolishing the expression and activity of KCa3.1 and PDGF β-receptors and inhibiting the rise in [Ca(2+)]i. The stimulation also attenuated the levels of phosphorylated CREB, c-Fos, and cyclin expression. After KCa3.1 blockade, the characteristic round shape of VSMCs expressing high l-caldesmon and low calponin-1 (dedifferentiation state) was maintained, whereas KCa3.1 stimulation induced a spindle-shaped cellular appearance, with low l-caldesmon and high calponin-1. In conclusion, KCa3.1 plays an important role in VSMC proliferation via controlling Ca(2+)-dependent signaling pathways, and its modulation may therefore constitute a new therapeutic target for cell proliferative diseases such as atherosclerosis.
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Affiliation(s)
- Dan Bi
- From the Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557
| | - Kazuyoshi Toyama
- the Department of Medicine and Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and
| | - Vincent Lemaître
- From the Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557
| | - Jun Takai
- From the Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557
| | - Fan Fan
- the Department of Medicine and Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and
| | - David P. Jenkins
- the Department of Pharmacology, University of California, Davis, California 95616
| | - Heike Wulff
- the Department of Pharmacology, University of California, Davis, California 95616
| | - David D. Gutterman
- the Department of Medicine and Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and
| | - Frank Park
- the Department of Medicine and Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and
| | - Hiroto Miura
- From the Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557
- the Department of Medicine and Cardiovascular Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53226, and
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5
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Abstract
The large conductance calcium- and voltage-activated potassium channel (BK(Ca)) is widely expressed at the plasma membrane. This channel is involved in a variety of fundamental cellular functions including excitability, smooth muscle contractility, and Ca(2+) homeostasis, as well as in pathological situations like proinflammatory responses in rheumatoid arthritis, and cancer cell proliferation. Immunochemical, biochemical and pharmacological studies from over a decade have intermittently shown the presence of BK(Ca) in intracellular organelles. To date, intracellular BK(Ca) (iBK(Ca)) has been localized in the mitochondria, endoplasmic reticulum, nucleus and Golgi apparatus but its functional role remains largely unknown except for the mitochondrial BK(Ca) whose opening is thought to play a role in protecting the heart from ischaemic injury. In the nucleus, pharmacology suggests a role in regulating nuclear Ca(2+), membrane potential and eNOS expression. Establishing the molecular correlates of iBK(Ca), the mechanisms defining iBK(Ca) organelle-specific targeting, and their modulation are challenging questions. This review summarizes iBK(Ca) channels, their possible functions, and efforts to identify their molecular correlates.
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Affiliation(s)
- Harpreet Singh
- Department of Anesthesiology, University of California, Los Angeles, CA 90095, USA
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Yamashita M. From neuroepithelial cells to neurons: changes in the physiological properties of neuroepithelial stem cells. Arch Biochem Biophys 2012; 534:64-70. [PMID: 22892549 DOI: 10.1016/j.abb.2012.07.016] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2012] [Revised: 07/04/2012] [Accepted: 07/27/2012] [Indexed: 10/28/2022]
Abstract
The central nervous system, which includes the spinal cord, retina, and brain, is derived from the neural tube. The neural tube is formed of a sheet of cells called the neuroepithelium. During embryonic development, neuroepithelial cells function as neural stem cells: they renew themselves while undergoing interkinetic nuclear movements along the apico-basal axis during the cell cycle, and they produce postmitotic cells that function as newborn neurons. Neuroepithelial cells exhibit a robust increase in nucleoplasmic [Ca(2+)] in response to G protein-coupled receptor activation during S-phase when the nucleus is located in the basal region of the cell. This Ca(2+) rise is caused by the release of Ca(2+) from intracellular Ca(2+) stores, and the Ca(2+) release in turn activates Ca(2+) entry from the extracellular space, which is called capacitative (or store-operated) Ca(2+) entry. The Ca(2+) release and store-operated Ca(2+) entry are essential for DNA synthesis during S-phase. The activity of this store-operated Ca(2+) signaling system declines in parallel with the decreasing proliferative activity of neuroepithelial cells. When exiting the cell cycle, the cells lose the apical process where gap junctions are located. Following the loss of gap junction coupling, the postmitotic cells show a high input resistance, which allows them to be readily depolarized. The Ca(2+) response to the excitatory neurotransmitter glutamate appears and develops during neuronal differentiation. The glutamate-induced Ca(2+) rise increases transiently during natural cell death (apoptosis). The rise in Ca(2+) levels mediated by voltage-gated Ca(2+) channels also develops during neuronal differentiation. Thus, when neuroepithelial cells differentiate into neurons, a transition from a store-operated system to a voltage-operated system occurs in the main Ca(2+) signaling system. This transition may reflect a change in the mode of intercellular communication from a stored Ca(2+)-dependent mode to a plasma membrane potential-dependent mode.
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Affiliation(s)
- Masayuki Yamashita
- Department of Physiology 1, Nara Medical University, Shijo-cho 840, Kashihara, Japan.
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Prole DL, Taylor CW. Identification and analysis of cation channel homologues in human pathogenic fungi. PLoS One 2012; 7:e42404. [PMID: 22876320 PMCID: PMC3410928 DOI: 10.1371/journal.pone.0042404] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Accepted: 07/05/2012] [Indexed: 01/08/2023] Open
Abstract
Fungi are major causes of human, animal and plant disease. Human fungal infections can be fatal, but there are limited options for therapy, and resistance to commonly used anti-fungal drugs is widespread. The genomes of many fungi have recently been sequenced, allowing identification of proteins that may become targets for novel therapies. We examined the genomes of human fungal pathogens for genes encoding homologues of cation channels, which are prominent drug targets. Many of the fungal genomes examined contain genes encoding homologues of potassium (K+), calcium (Ca2+) and transient receptor potential (Trp) channels, but not sodium (Na+) channels or ligand-gated channels. Some fungal genomes contain multiple genes encoding homologues of K+ and Trp channel subunits, and genes encoding novel homologues of voltage-gated Kv channel subunits are found in Cryptococcus spp. Only a single gene encoding a homologue of a plasma membrane Ca2+ channel was identified in the genome of each pathogenic fungus examined. These homologues are similar to the Cch1 Ca2+ channel of Saccharomyces cerevisiae. The genomes of Aspergillus spp. and Cryptococcus spp., but not those of S. cerevisiae or the other pathogenic fungi examined, also encode homologues of the mitochondrial Ca2+ uniporter (MCU). In contrast to humans, which express many K+, Ca2+ and Trp channels, the genomes of pathogenic fungi encode only very small numbers of K+, Ca2+ and Trp channel homologues. Furthermore, the sequences of fungal K+, Ca2+, Trp and MCU channels differ from those of human channels in regions that suggest differences in regulation and susceptibility to drugs.
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Affiliation(s)
- David L Prole
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, United Kingdom.
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Ion channel activities in neural stem cells of the neuroepithelium. Stem Cells Int 2012; 2012:247670. [PMID: 22848227 PMCID: PMC3398652 DOI: 10.1155/2012/247670] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Revised: 05/02/2012] [Accepted: 05/09/2012] [Indexed: 12/12/2022] Open
Abstract
During the embryonic development of the central nervous system, neuroepithelial cells act as neural stem cells. They undergo interkinetic nuclear movements along their apico-basal axis during the cell cycle. The neuroepithelial cell shows robust increases in the nucleoplasmic [Ca2+] in response to G protein-coupled receptor activation in S-phase, during which the nucleus is located in the basal region of the neuroepithelial cell. This response is caused by Ca2+ release from intracellular Ca2+ stores, which are comprised of the endoplasmic reticulum and the nuclear envelope. The Ca2+ release leads to the activation of Ca2+ entry from the extracellular space, which is called capacitative, or store-operated Ca2+ entry. These movements of Ca2+ are essential for DNA synthesis during S-phase. Spontaneous Ca2+ oscillations also occur synchronously across the cells. This synchronization is mediated by voltage fluctuations in the membrane potential of the nuclear envelope due to Ca2+ release and the counter movement of K+ ions; the voltage fluctuation induces alternating current (AC), which is transmitted via capacitative electrical coupling to the neighboring cells. The membrane potential across the plasma membrane is stabilized through gap junction coupling by lowering the input resistance. Thus, stored Ca2+ ions are a key player in the maintenance of the cellular activity of neuroepithelial cells.
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9
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Large conductance, calcium- and voltage-gated potassium (BK) channels: regulation by cholesterol. Pharmacol Ther 2012; 135:133-50. [PMID: 22584144 DOI: 10.1016/j.pharmthera.2012.05.002] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Accepted: 04/09/2012] [Indexed: 11/21/2022]
Abstract
Cholesterol (CLR) is an essential component of eukaryotic plasma membranes. CLR regulates the membrane physical state, microdomain formation and the activity of membrane-spanning proteins, including ion channels. Large conductance, voltage- and Ca²⁺-gated K⁺ (BK) channels link membrane potential to cell Ca²⁺ homeostasis. Thus, they control many physiological processes and participate in pathophysiological mechanisms leading to human disease. Because plasmalemma BK channels cluster in CLR-rich membrane microdomains, a major driving force for studying BK channel-CLR interactions is determining how membrane CLR controls the BK current phenotype, including its pharmacology, channel sorting, distribution, and role in cell physiology. Since both BK channels and CLR tissue levels play a pathophysiological role in human disease, identifying functional and structural aspects of the CLR-BK channel interaction may open new avenues for therapeutic intervention. Here, we review the studies documenting membrane CLR-BK channel interactions, dissecting out the many factors that determine the final BK current response to changes in membrane CLR content. We also summarize work in reductionist systems where recombinant BK protein is studied in artificial lipid bilayers, which documents a direct inhibition of BK channel activity by CLR and builds a strong case for a direct interaction between CLR and the BK channel-forming protein. Bilayer lipid-mediated mechanisms in CLR action are also discussed. Finally, we review studies of BK channel function during hypercholesterolemia, and underscore the many consequences that the CLR-BK channel interaction brings to cell physiology and human disease.
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Prole DL, Marrion NV. Identification of putative potassium channel homologues in pathogenic protozoa. PLoS One 2012; 7:e32264. [PMID: 22363819 PMCID: PMC3283738 DOI: 10.1371/journal.pone.0032264] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2011] [Accepted: 01/24/2012] [Indexed: 12/21/2022] Open
Abstract
K+ channels play a vital homeostatic role in cells and abnormal activity of these channels can dramatically alter cell function and survival, suggesting that they might be attractive drug targets in pathogenic organisms. Pathogenic protozoa lead to diseases such as malaria, leishmaniasis, trypanosomiasis and dysentery that are responsible for millions of deaths each year worldwide. The genomes of many protozoan parasites have recently been sequenced, allowing rational design of targeted therapies. We analyzed the genomes of pathogenic protozoa and show the existence within them of genes encoding putative homologues of K+ channels. These protozoan K+ channel homologues represent novel targets for anti-parasitic drugs. Differences in the sequences and diversity of human and parasite proteins may allow pathogen-specific targeting of these K+ channel homologues.
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Affiliation(s)
- David L Prole
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom.
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11
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Kuum M, Veksler V, Liiv J, Ventura-Clapier R, Kaasik A. Endoplasmic reticulum potassium–hydrogen exchanger and small conductance calcium-activated potassium channel activities are essential for ER calcium uptake in neurons and cardiomyocytes. J Cell Sci 2012; 125:625-33. [DOI: 10.1242/jcs.090126] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Calcium pumping into the endoplasmic reticulum (ER) lumen is thought to be coupled to a countertransport of protons through sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) and the members of the ClC family of chloride channels. However, pH in the ER lumen remains neutral, which suggests a mechanism responsible for proton re-entry. We studied whether cation–proton exchangers could act as routes for such a re-entry. ER Ca2+ uptake was measured in permeabilized immortalized hypothalamic neurons, primary rat cortical neurons and mouse cardiac fibers. Replacement of K+ in the uptake solution with Na+ or tetraethylammonium led to a strong inhibition of Ca2+ uptake in neurons and cardiomyocytes. Furthermore, inhibitors of the potassium–proton exchanger (quinine or propranolol) but not of the sodium–proton exchanger reduced ER Ca2+ uptake by 56–82%. Externally added nigericin, a potassium–proton exchanger, attenuated the inhibitory effect of propranolol. Inhibitors of small conductance calcium-sensitive K+ (SKCa) channels (UCL 1684, dequalinium) blocked the uptake of Ca2+ by the ER in all preparations by 48–94%, whereas inhibitors of other K+ channels (IKCa, BKCa and KATP) had no effect. Fluorescence microscopy and western blot analysis revealed the presence of both SKCa channels and the potassium–proton exchanger leucine zipper-EF-hand-containing transmembrane protein 1 (LETM1) in ER in situ and in the purified ER fraction. The data obtained demonstrate that SKCa channels and LETM1 reside in the ER membrane and that their activity is essential for ER Ca2+ uptake.
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Affiliation(s)
- Malle Kuum
- Department of Pharmacology, Centre of Excellence for Translational Medicine, University of Tartu, Ravila 19, Tartu EE-51014, Estonia
- INSERM, U-769, 5, rue Jean-Baptiste Clement, Châtenay-Malabry F-92296, France
- Université Paris-Sud, 5, rue Jean-Baptiste Clement, Châtenay-Malabry F-92296, France
| | - Vladimir Veksler
- INSERM, U-769, 5, rue Jean-Baptiste Clement, Châtenay-Malabry F-92296, France
- Université Paris-Sud, 5, rue Jean-Baptiste Clement, Châtenay-Malabry F-92296, France
| | - Joanna Liiv
- Department of Pharmacology, Centre of Excellence for Translational Medicine, University of Tartu, Ravila 19, Tartu EE-51014, Estonia
| | - Renee Ventura-Clapier
- INSERM, U-769, 5, rue Jean-Baptiste Clement, Châtenay-Malabry F-92296, France
- Université Paris-Sud, 5, rue Jean-Baptiste Clement, Châtenay-Malabry F-92296, France
| | - Allen Kaasik
- Department of Pharmacology, Centre of Excellence for Translational Medicine, University of Tartu, Ravila 19, Tartu EE-51014, Estonia
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Abstract
Calcium plays important role in biological systems where it is involved in diverse mechanisms such as signaling, muscle contraction and neuromodulation. Action potentials are generated by dynamic interaction of ionic channels located on the plasma-membrane and these drive the rhythmic activity of biological systems such as the smooth muscle and the heart. However, ionic channels are not the only pacemakers; an intimate interaction between intracellular Ca(2+) stores and ionic channels underlie rhythmic activity. In this review we will focus on the role of Ca(2+) stores in regulation of rhythmical behavior.
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Affiliation(s)
- Mohammad S Imtiaz
- Department of Physiology & Pharmacology, Faculty of Medicine, University of Calgary, Health Sciences Centre, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada.
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13
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Conserved BK channel-protein interactions reveal signals relevant to cell death and survival. PLoS One 2011; 6:e28532. [PMID: 22174833 PMCID: PMC3235137 DOI: 10.1371/journal.pone.0028532] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 11/09/2011] [Indexed: 12/28/2022] Open
Abstract
The large-conductance Ca2+-activated K+ (BK) channel and its β-subunit underlie tuning in non-mammalian sensory or hair cells, whereas in mammals its function is less clear. To gain insights into species differences and to reveal putative BK functions, we undertook a systems analysis of BK and BK-Associated Proteins (BKAPS) in the chicken cochlea and compared these results to other species. We identified 110 putative partners from cytoplasmic and membrane/cytoskeletal fractions, using a combination of coimmunoprecipitation, 2-D gel, and LC-MS/MS. Partners included 14-3-3γ, valosin-containing protein (VCP), stathmin (STMN), cortactin (CTTN), and prohibitin (PHB), of which 16 partners were verified by reciprocal coimmunoprecipitation. Bioinformatics revealed binary partners, the resultant interactome, subcellular localization, and cellular processes. The interactome contained 193 proteins involved in 190 binary interactions in subcellular compartments such as the ER, mitochondria, and nucleus. Comparisons with mice showed shared hub proteins that included N-methyl-D-aspartate receptor (NMDAR) and ATP-synthase. Ortholog analyses across six species revealed conserved interactions involving apoptosis, Ca2+ binding, and trafficking, in chicks, mice, and humans. Functional studies using recombinant BK and RNAi in a heterologous expression system revealed that proteins important to cell death/survival, such as annexinA5, γ-actin, lamin, superoxide dismutase, and VCP, caused a decrease in BK expression. This revelation led to an examination of specific kinases and their effectors relevant to cell viability. Sequence analyses of the BK C-terminus across 10 species showed putative binding sites for 14-3-3, RAC-α serine/threonine-protein kinase 1 (Akt), glycogen synthase kinase-3β (GSK3β) and phosphoinositide-dependent kinase-1 (PDK1). Knockdown of 14-3-3 and Akt caused an increase in BK expression, whereas silencing of GSK3β and PDK1 had the opposite effect. This comparative systems approach suggests conservation in BK function across different species in addition to novel functions that may include the initiation of signals relevant to cell death/survival.
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14
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Fedorenko EA, Semenova OV, Marchenko SM. Properties of Large-Conductance Cationic Channels in the Neuronal Nuclear Envelope. NEUROPHYSIOLOGY+ 2011. [DOI: 10.1007/s11062-011-9202-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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15
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Sakai Y, Harvey M, Sokolowski B. Identification and quantification of full-length BK channel variants in the developing mouse cochlea. J Neurosci Res 2011; 89:1747-60. [PMID: 21800349 DOI: 10.1002/jnr.22713] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Revised: 04/28/2011] [Accepted: 05/12/2011] [Indexed: 01/03/2023]
Abstract
Maxi-K(+) (BK) channel diversity is attributed to alternative splicing in the kcnma1 gene. The resultant variants manifest themselves in different cell types, tissues, and functions, such as excitation, metabolism, and signaling. Immunoelectron microscopy revealed immunogold particle labeling of BK in apical and basal regions of inner and outer hair cells, respectively. Additional labeling occurs in Deiters' cells and the inner mitochondrial membrane. Identification of full-length sequences reveals 27 BK variants from embryonic and postnatal mouse inner ear, per classification by tail motif, VYR, DEC, and ERL, and by exon usage. Three predicted start codons are found encoding MAN, MSS, and MDA, of which MDA shows the greatest expression through all stages in development, whereas MAN is undetectable. Complex splice sites occur between exons 9 and 10 and between 21 and 23. Spliced-in/out exons between 8 and 10 reveal a short fragment composed of exons 8 + 10, detectable on postnatal day (PD) 14 and PD30, and a longer fragment composed of exons 8 + 9 + 10 that is upregulated on embryonic day (ED) 14. Spliced-in exons 22 or 23 are expressed on ED14 but decrease over time; however, exon 22 increases again on PD34. Using tail-specific primers, qRT-PCR from ED14, PD4, -14, and -30 shows that BK-VYR and -ERL dominate expression on ED14, whereas DEC dominates after birth in all cochlear regions. The localization of BK and the changes in expression of its exons and tail types, by alternative splicing during development, may contribute to cochlear organization, acquisition of hearing, and intracellular signaling.
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Affiliation(s)
- Yoshihisa Sakai
- Department of Otolaryngology-Head and Neck Surgery, University of South Florida, Tampa, Florida 33612, USA
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Yamashita M. Fluctuations in nuclear envelope's potential mediate synchronization of early neural activity. Biochem Biophys Res Commun 2011; 406:107-11. [PMID: 21296053 DOI: 10.1016/j.bbrc.2011.02.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2011] [Accepted: 02/01/2011] [Indexed: 01/18/2023]
Abstract
Neural progenitor cells and developing neurons show periodic, synchronous Ca(2+) rises even before synapse formation, and the origin of the synchronous activity remains unknown. Here, fluorescence measurement revealed that the membrane potential of the nuclear envelope, which forms an intracellular Ca(2+) store, changed with a release of Ca(2+) and generated spontaneous, periodic bursts of fluctuations in potential. Furthermore, changes in the nuclear envelope's potential underlay spike burst generations. These results support the model that voltage fluctuations of the nuclear envelope synchronize Ca(2+) release between cells and also function as a current noise generator to cause synchronous burst discharges.
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Affiliation(s)
- Masayuki Yamashita
- Department of Physiology I, Nara Medical University, Shijo-cho 840, Kashihara 634-8521, Japan.
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Importance of Cationic Channels for Functioning of the Nuclear Envelope of Neurons as a Calcium Store. NEUROPHYSIOLOGY+ 2011. [DOI: 10.1007/s11062-011-9154-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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18
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Fedorenko OA, Marchenko SM. Spontaneously active ion channels of the nuclear envelope membrane. ACTA ACUST UNITED AC 2010. [DOI: 10.15407/fz56.05.095] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Fedorenko EA, Duzhii DE, Marchenko SM. Voltage Dependence of the Activity of Inositol Trisphosphate Receptors of the Nuclear Envelope of Hippocampal Pyramidal Neurons. NEUROPHYSIOLOGY+ 2010. [DOI: 10.1007/s11062-010-9106-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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20
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Imtiaz MS, von der Weid PY, van Helden DF. Synchronization of Ca2+ oscillations: a coupled oscillator-based mechanism in smooth muscle. FEBS J 2009; 277:278-85. [PMID: 19895582 DOI: 10.1111/j.1742-4658.2009.07437.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Entrained oscillations in Ca(2+) underlie many biological pacemaking phenomena. In this article, we review a long-range signaling mechanism in smooth muscle that results in global outcomes of local interactions. Our results are derived from studies of the following: (a) slow-wave depolarizations that underlie rhythmic contractions of gastric smooth muscle; and (b) membrane depolarizations that drive rhythmic contractions of lymphatic smooth muscle. The main feature of this signaling mechanism is a coupled oscillator-based synchronization of Ca(2+) oscillations across cells that drives membrane potential changes and causes coordinated contractions. The key elements of this mechanism are as follows: (a) the Ca(2+) release-refill cycle of endoplasmic reticulum Ca(2+) stores; (b) Ca(2+)-dependent modulation of membrane currents; (c) voltage-dependent modulation of Ca(2+) store release; and (d) cell-cell coupling through gap junctions or other mechanisms. In this mechanism, Ca(2+) stores alter the frequency of adjacent stores through voltage-dependent modulation of store release. This electrochemical coupling is many orders of magnitude stronger than the coupling through diffusion of Ca(2+) or inositol 1,4,5-trisphosphate, and thus provides an effective means of long-range signaling.
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Affiliation(s)
- Mohammad S Imtiaz
- Department of Physiology and Pharmacology, University of Calgary, Alberta, Canada.
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Yamashita M. Synchronization of Ca2+ oscillations: a capacitative (AC) electrical coupling model in neuroepithelium. FEBS J 2009; 277:293-9. [PMID: 19895580 DOI: 10.1111/j.1742-4658.2009.07439.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Increases in intracellular [Ca(2+)] occur synchronously between cells in the neuroepithelium. If neuroepithelial cells were capable of generating action potentials synchronized by gap junctions (direct current electrical coupling), the influx of Ca(2+) through voltage-activated Ca(2+) channels would lead to a synchronous increase in intracellular [Ca(2+)]. However, no action potential is generated in neuroepithelial cells, and the [Ca(2+)] increase is instead produced by the release of Ca(2+) from intracellular Ca(2+) stores. Recently, synchronous fluctuations in the membrane potential of Ca(2+) stores were recorded using an organelle-specific voltage-sensitive dye. On the basis of these recordings, a capacitative [alternating current (AC)] electrical coupling model for the synchronization of voltage fluctuations of Ca(2+) store potential was proposed [Yamashita M (2006) FEBS Lett580, 4979-4983; Yamashita M (2008) FEBS J275, 4022-4032]. Ca(2+) efflux from the Ca(2+) store and K(+) counterinflux into the store cause alternating voltage changes across the store membrane, and the voltage fluctuation induces ACs. In cases where the store membrane is closely apposed to the plasma membrane and the cells are tightly packed, which is true of neuroepithelial cells, the voltage fluctuation of the store membrane is synchronized between the cells by the AC currents through the series capacitance of these membranes. This article provides a short review of the model and its relationship to the structural organization of the Ca(2+) store. This is followed by a discussion of how the mode of synchronization of [Ca(2+)] increase may change during central nervous system development and new molecular insights into the synchronicity of [Ca(2+)] increase.
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22
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Kathiresan T, Harvey M, Orchard S, Sakai Y, Sokolowski B. A protein interaction network for the large conductance Ca(2+)-activated K(+) channel in the mouse cochlea. Mol Cell Proteomics 2009; 8:1972-87. [PMID: 19423573 PMCID: PMC2722780 DOI: 10.1074/mcp.m800495-mcp200] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Revised: 05/06/2009] [Indexed: 12/21/2022] Open
Abstract
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 BKalpha expression in CHO cells. Studies of BKalpha 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.
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Affiliation(s)
- Thandavarayan Kathiresan
- From the ‡Department of Otolaryngology – Head and Neck Surgery, University of South Florida, College of Medicine, Tampa, Florida 33612 and
| | - Margaret Harvey
- From the ‡Department of Otolaryngology – Head and Neck Surgery, University of South Florida, College of Medicine, Tampa, Florida 33612 and
| | - Sandra Orchard
- §European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton Cambridge, CB10 1SD, United Kingdom
| | - Yoshihisa Sakai
- From the ‡Department of Otolaryngology – Head and Neck Surgery, University of South Florida, College of Medicine, Tampa, Florida 33612 and
| | - Bernd Sokolowski
- From the ‡Department of Otolaryngology – Head and Neck Surgery, University of South Florida, College of Medicine, Tampa, Florida 33612 and
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The large-conductance Ca(2+)-activated K(+) channel interacts with the apolipoprotein ApoA1. Biochem Biophys Res Commun 2009; 387:671-5. [PMID: 19619511 DOI: 10.1016/j.bbrc.2009.07.074] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Accepted: 07/14/2009] [Indexed: 01/01/2023]
Abstract
Owing to the multifaceted functions of the large conductance Ca(2+)-activated K(+) channel (BK), identification of protein-protein interactions is essential in determining BK regulation. A yeast two-hybrid screening of a cochlear cDNA library revealed a BK-ApoA1 interaction. Patch clamp recordings of excised membrane patches from transfected HEK293 cells showed that ApoA1 inhibits the BK alpha-subunit by significantly increasing activation and deactivation times, and shifting half-activation voltage to more positive potentials. Reciprocal coimmunoprecipitations verified the BK-ApoA1 interaction using excised sensory epithelium and ganglia. Additionally, immunocolocalization studies revealed BK and ApoA1 expression in both receptor cells and auditory neurons. These data suggest new avenues of investigation, given the importance of apolipoproteins in neurological diseases.
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Sekiguchi-Tonosaki M, Obata M, Haruki A, Himi T, Kosaka J. Acetylcholine induces Ca2+ signaling in chicken retinal pigmented epithelial cells during dedifferentiation. Am J Physiol Cell Physiol 2009; 296:C1195-206. [PMID: 19244481 DOI: 10.1152/ajpcell.00423.2008] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Retinal pigmented epithelial cells exchange their cellular phenotypes into lens cells and neurons, via depigmented and non-epithelial-shaped dedifferentiated intermediates. Because these dedifferentiated cells can either revert to pigmented epithelial cells or transdifferentiate into lens cells and/or neurons, they are recognized as candidates for lens and retinal cell regeneration. The purpose of the present study was to elucidate the signal transduction pathways between chicken retinal pigmented epithelial cells and their dedifferentiated intermediates. We monitored intracellular Ca(2+) concentrations using Fluo-4-based Ca(2+) optical imaging and focused on cellular responses to the neurotransmitter acetylcholine. Muscarinic Ca(2+) mobilization was observed both in retinal pigmented epithelial cells and in dedifferentiated cells, and was inhibited by atropine. The muscarine-dependent acetylcholine response depended on Ca(2+) release from intracellular Ca(2+) stores, which was completely blocked by thapsigargin. In contrast, the nicotine-dependent acetylcholine response that led to Ca(2+) influx through L-type Ca(2+) channels was inhibited by alpha-bungarotoxin and attenuated by nifedipine, and it was detected only in the dedifferentiated intermediates. Application of (S)-(-)-BayK8644 elevated intracellular Ca(2+) both in retinal pigmented epithelial cells and in dedifferentiated intermediates; however, the nicotinic response was not observed in pigmented epithelial cells. Another L-type Ca(2+) channel blocker, diltiazem, also blocked the nicotine-dependent acetylcholine response in dedifferentiated cells and maintained the epithelial-like morphology of retinal pigmented epithelial cells. Our results indicate that an alternative acetylcholine signaling pathway is used during the dedifferentiation process of retinal pigmented epithelial cells.
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Affiliation(s)
- Mariko Sekiguchi-Tonosaki
- Dept. of Cytology and Histology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Okayama 700-8558, Japan
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Pacheco Otalora LF, Hernandez EF, Arshadmansab MF, rancisco SF, Willis M, Ermolinsky B, Zarei M, Knaus HG, Garrido-Sanabria ER. Down-regulation of BK channel expression in the pilocarpine model of temporal lobe epilepsy. Brain Res 2008; 1200:116-31. [PMID: 18295190 PMCID: PMC2346580 DOI: 10.1016/j.brainres.2008.01.017] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2007] [Revised: 12/23/2007] [Accepted: 01/03/2008] [Indexed: 11/24/2022]
Abstract
In the hippocampus, BK channels are preferentially localized in presynaptic glutamatergic terminals including mossy fibers where they are thought to play an important role regulating excessive glutamate release during hyperactive states. Large conductance calcium-activated potassium channels (BK, MaxiK, Slo) have recently been implicated in the pathogenesis of genetic epilepsy. However, the role of BK channels in acquired mesial temporal lobe epilepsy (MTLE) remains unknown. Here we used immunohistochemistry, laser scanning confocal microscopy (LSCM), Western immunoblotting and RT-PCR to investigate the expression pattern of the alpha-pore-forming subunit of BK channels in the hippocampus and cortex of chronically epileptic rats obtained by the pilocarpine model of MTLE. All epileptic rats experiencing recurrent spontaneous seizures exhibited a significant down-regulation of BK channel immunostaining in the mossy fibers at the hilus and stratum lucidum of the CA3 area. Quantitative analysis of immunofluorescence signals by LSCM revealed a significant 47% reduction in BK channel immunofluorescent signals in epileptic rats when compared to age-matched non-epileptic control rats. These data correlate with a similar reduction in BK channel protein levels and transcripts in the cortex and hippocampus. Our data indicate a seizure-related down-regulation of BK channels in chronically epileptic rats. Further functional assays are necessary to determine whether altered BK channel expression is an acquired channelopathy or a compensatory mechanism affecting the network excitability in MTLE. Moreover, seizure-mediated BK down-regulation may disturb neuronal excitability and presynaptic control at glutamatergic terminals triggering exaggerated glutamate release and seizures.
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Affiliation(s)
- Luis F. Pacheco Otalora
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
| | - Eder F. Hernandez
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
| | - Massoud F. Arshadmansab
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
| | - Sebastian F rancisco
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
| | - Michael Willis
- Department of General Psychiatry, Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria
- Department of Molecular and Cellular Pharmacology, Medical University Innsbruck, Peter-Mayr Strasse 1, 6020 Innsbruck, Austria
| | - Boris Ermolinsky
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
| | - Masoud Zarei
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
- The Center for Biomedical Studies, Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria
| | - Hans-Guenther Knaus
- Department of Molecular and Cellular Pharmacology, Medical University Innsbruck, Peter-Mayr Strasse 1, 6020 Innsbruck, Austria
| | - Emilio R. Garrido-Sanabria
- Department of Biological Sciences at the University of Texas at Brownsville/Texas Southmost College, Brownsville, Texas 78520 USA
- The Center for Biomedical Studies, Medical University Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria
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Fedorenko EA, Dyzhii DE, Marchenko SM. Large-conductance cationic channels in the nuclear envelope of Purkinje neurons from the rat cerebellum. NEUROPHYSIOLOGY+ 2007. [DOI: 10.1007/s11062-007-0014-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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28
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Yamashita M. ‘Quantal’ Ca2+release reassessed - a clue to oscillation and synchronization. FEBS Lett 2006; 580:4979-83. [PMID: 16938295 DOI: 10.1016/j.febslet.2006.08.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Accepted: 08/14/2006] [Indexed: 11/26/2022]
Abstract
Ca(2+) release from intracellular Ca(2+) stores, a pivotal event in Ca(2+) signaling, is a 'quantal' process; it terminates after a rapid release of a fraction of stored Ca(2+). To explain the 'quantal' nature, 'all-or-none' model and 'steady-state' model were proposed. This article shortly reviews these hypotheses and considers a recently proposed mechanism, 'luminal potential' model, in which the membrane potential of Ca(2+) store regulates Ca(2+) efflux. By reassessing the 'quantal' nature, other important features of Ca(2+) signaling, oscillation and synchronization, are highlighted. The mechanism for 'quantal' Ca(2+) release may underlie the temporal and spatial control of Ca(2+) signaling.
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Affiliation(s)
- Masayuki Yamashita
- Department of Physiology I, Nara Medical University, Shijo-cho 840, Kashihara 634-8521, Japan.
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