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Abstract
Due to its high external and low internal concentration the Ca(2+) ion is used ubiquitously as an intracellular signaling molecule, and a great many Ca(2+)-sensing proteins have evolved to receive and propagate Ca(2+) signals. Among them are ion channel proteins, whose Ca(2+) sensitivity allows internal Ca(2+) to influence the electrical activity of cell membranes and to feedback-inhibit further Ca(2+) entry into the cytoplasm. In this review I will describe what is understood about the Ca(2+) sensing mechanisms of the three best studied classes of Ca(2+)-sensitive ion channels: Large-conductance Ca(2+)-activated K(+) channels, small-conductance Ca(2+)-activated K(+) channels, and voltage- gated Ca(2+) channels. Great strides in mechanistic understanding have be made for each of these channel types in just the past few years.
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Affiliation(s)
- Daniel H Cox
- Department of Neuroscience, Tufts University School of Medicine, Boston MA, 02420, USA.
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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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53
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Inhibition of the Ca²⁺-dependent K⁺ channel, KCNN4/KCa3.1, improves tissue protection and locomotor recovery after spinal cord injury. J Neurosci 2012; 31:16298-308. [PMID: 22072681 DOI: 10.1523/jneurosci.0047-11.2011] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Spinal cord injury (SCI) triggers inflammatory responses that involve neutrophils, macrophages/microglia and astrocytes and molecules that potentially cause secondary tissue damage and functional impairment. Here, we assessed the contribution of the calcium-dependent K⁺ channel KCNN4 (KCa3.1, IK1, SK4) to secondary damage after moderate contusion lesions in the lower thoracic spinal cord of adult mice. Changes in KCNN4 mRNA levels (RT-PCR), KCa3.1 protein expression (Western blots), and cellular expression (immunofluorescence) in the mouse spinal cord were monitored between 1 and 28 d after SCI. KCNN4 mRNA and KCa3.1 protein rapidly increased after SCI; double labeling identified astrocytes as the main cellular source accounting for this upregulation. Locomotor function after SCI, evaluated for 28 d in an open-field test using the Basso Mouse Scale, was improved in a dose-dependent manner by treating mice with a selective inhibitor of KCa3.1 channels, TRAM-34 (triarylmethane-34). Improved locomotor function was accompanied by reduced tissue loss at 28 d and increased neuron and axon sparing. The rescue of tissue by TRAM-34 treatment was preceded by reduced expression of the proinflammatory mediators, tumor necrosis factor-α and interleukin-1β in spinal cord tissue at 12 h after injury, and reduced expression of inducible nitric oxide synthase at 7 d after SCI. In astrocytes in vitro, TRAM-34 inhibited Ca²⁺ signaling in response to metabotropic purinergic receptor stimulation. These results suggest that blocking the KCa3.1 channel could be a potential therapeutic approach for treating secondary damage after spinal cord injury.
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54
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Jin M, Berrout J, Chen L, O'Neil RG. Hypotonicity-induced TRPV4 function in renal collecting duct cells: modulation by progressive cross-talk with Ca2+-activated K+ channels. Cell Calcium 2011; 51:131-9. [PMID: 22204737 DOI: 10.1016/j.ceca.2011.11.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 11/11/2011] [Accepted: 11/29/2011] [Indexed: 12/16/2022]
Abstract
The mouse cortical collecting duct (CCD) M-1 cells were grown to confluency on coverslips to assess the interaction between TRPV4 and Ca(2+)-activated K(+) channels. Immunocytochemistry demonstrated strong expression of TRPV4, along with the CCD marker, aquaporin-2, and the Ca(2+)-activated K(+) channels, the small conductance SK3 (K(Ca)2.3) channel and large conductance BKα channel (K(Ca)1.1). TRPV4 overexpression studies demonstrated little physical dependency of the K(+) channels on TRPV4. However, activation of TRPV4 by hypotonic swelling (or GSK1016790A, a selective agonist) or inhibition by the selective antagonist, HC-067047, demonstrated a strong dependency of SK3 and BK-α activation on TRPV4-mediated Ca(2+) influx. Selective inhibition of BK-α channel (Iberiotoxin) or SK3 channel (apamin), thereby depolarizing the cells, further revealed a significant dependency of TRPV4-mediated Ca(2+) influx on activation of both K(+) channels. It is concluded that a synergistic cross-talk exists between the TRPV4 channel and SK3 and BK-α channels to provide a tight functional regulation between the channel groups. This cross-talk may be progressive in nature where the initial TRPV4-mediated Ca(2+) influx would first activate the highly Ca(2+)-sensitive SK3 channel which, in turn, would lead to enhanced Ca(2+) influx and activation of the less Ca(2+)-sensitive BK channel.
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Affiliation(s)
- Min Jin
- Dept. of Integrative Biology and Pharmacology, The University of Texas Health Science Center, Houston, TX 77030, USA
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55
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Edelmann E, Lessmann V. Dopamine Modulates Spike Timing-Dependent Plasticity and Action Potential Properties in CA1 Pyramidal Neurons of Acute Rat Hippocampal Slices. Front Synaptic Neurosci 2011; 3:6. [PMID: 22065958 PMCID: PMC3207259 DOI: 10.3389/fnsyn.2011.00006] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Accepted: 10/17/2011] [Indexed: 12/25/2022] Open
Abstract
Spike timing-dependent plasticity (STDP) is a cellular model of Hebbian synaptic plasticity which is believed to underlie memory formation. In an attempt to establish a STDP paradigm in CA1 of acute hippocampal slices from juvenile rats (P15–20), we found that changes in excitability resulting from different slice preparation protocols correlate with the success of STDP induction. Slice preparation with sucrose containing ACSF prolonged rise time, reduced frequency adaptation, and decreased latency of action potentials in CA1 pyramidal neurons compared to preparation in conventional ASCF, while other basal electrophysiological parameters remained unaffected. Whereas we observed prominent timing-dependent long-term potentiation (t-LTP) to 171 ± 10% of controls in conventional ACSF, STDP was absent in sucrose prepared slices. This sucrose-induced STDP deficit could not be rescued by stronger STDP paradigms, applying either more pre- and/or postsynaptic stimuli, or by a higher stimulation frequency. Importantly, slice preparation with sucrose containing ACSF did not eliminate theta-burst stimulation induced LTP in CA1 in field potential recordings in our rat hippocampal slices. Application of dopamine (for 10–20 min) to sucrose prepared slices completely rescued t-LTP and recovered action potential properties back to levels observed in ACSF prepared slices. Conversely, acute inhibition of D1 receptor signaling impaired t-LTP in ACSF prepared slices. No similar restoring effect for STDP as seen with dopamine was observed in response to the β-adrenergic agonist isoproterenol. ELISA measurements demonstrated a significant reduction of endogenous dopamine levels (to 61.9 ± 6.9% of ACSF values) in sucrose prepared slices. These results suggest that dopamine signaling is involved in regulating the efficiency to elicit STDP in CA1 pyramidal neurons.
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Affiliation(s)
- Elke Edelmann
- Institute of Physiology, Medical School, Otto-von-Guericke University Magdeburg Magdeburg, Germany
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56
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Synthesis and radioligand binding studies of bis-(8-isopropyl-isoquinolinium) derivatives as ligands for apamin-sensitive sites on cloned SK2 and SK3 channels. Bioorg Med Chem Lett 2011; 21:6756-9. [DOI: 10.1016/j.bmcl.2011.09.043] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 09/08/2011] [Accepted: 09/13/2011] [Indexed: 11/20/2022]
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de Oliveira RW, Martin S, de Oliveira CL, Milani H, Schiavon A, Joca S, Pardo L, Stühmer W, Del Bel E. Eag1, Eag2, and SK3 potassium channel expression in the rat hippocampus after global transient brain ischemia. J Neurosci Res 2011; 90:632-40. [DOI: 10.1002/jnr.22772] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Revised: 07/19/2011] [Accepted: 07/28/2011] [Indexed: 11/08/2022]
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58
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Braun MH, Lukowiak K. Intermediate and long-term memory are different at the neuronal level in Lymnaea stagnalis (L.). Neurobiol Learn Mem 2011; 96:403-16. [PMID: 21757019 DOI: 10.1016/j.nlm.2011.06.016] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Revised: 06/26/2011] [Accepted: 06/29/2011] [Indexed: 12/25/2022]
Abstract
Both intermediate-term memory (ITM) and long-term memory (LTM) require novel protein synthesis; however, LTM also requires gene transcription. This suggests that the behavioural output of the two processes may be produced differently at the neuronal level. The fresh-water snail, Lymnaea stagnalis, can be operantly conditioned to decrease its rate of aerial respiration and, depending on the training procedure, the memory can last 3h (ITM) or >24h (LTM). RPeD1, one of the 3 interneurons that form the respiratory central pattern generator (CPG) that drives aerial respiration, is necessary for memory formation. By comparing RPeD1's electrophysiological properties in naïve, 'ITM-trained', 'LTM-trained' and yoked control snails we discovered that while the behavioural phenotype of memory at 3 and 24h is identical, the situation at the neuronal level is different. When examined 3h after either the 'ITM' or 'LTM' training procedure RPeD1 activity is significantly depressed. That is, the firing rate, input resistance, excitability and the number of action potential bursts are all significantly decreased. In snails receiving the ITM-training, these changes return to normal 24h post-training. However, in snails receiving the 'LTM-training', measured RPeD1 properties (firing rate, excitability, membrane resistance, and the number of action potential bursts fired) are significantly different at 24h than they were at 3h. Additionally, 24h following LTM training RPeD1 appears to be functionally "uncoupled" from its control of the pneumostome as the link between RPeD1 excitation and pneumostome opening is weakened. These data suggest that the behavioural changes occurring during LTM are due to more widespread neuronal reorganization than similar behavioural changes occurring during ITM. Thus ITM and LTM are not just distinct in a chronological and transcriptional manner but are also distinct at the level of neuronal properties.
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Affiliation(s)
- Marvin H Braun
- Hotchkiss Brain Institute, Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, Canada.
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59
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Mulholland PJ, Becker HC, Woodward JJ, Chandler LJ. Small conductance calcium-activated potassium type 2 channels regulate alcohol-associated plasticity of glutamatergic synapses. Biol Psychiatry 2011; 69:625-32. [PMID: 21056409 PMCID: PMC3103782 DOI: 10.1016/j.biopsych.2010.09.025] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/24/2010] [Revised: 09/08/2010] [Accepted: 09/10/2010] [Indexed: 01/22/2023]
Abstract
BACKGROUND Small conductance calcium-activated potassium type 2 channels (SK2) control excitability and contribute to plasticity by reducing excitatory postsynaptic potentials. Recent evidence suggests that SK2 channels form a calcium-dependent negative-feedback loop with synaptic N-methyl-D-aspartate (NMDA) receptors. Addiction to alcohol and other drugs of abuse induces plastic changes in glutamatergic synapses that include the targeting of NMDA receptors to synaptic sites; however, the role of SK2 channels in alcohol-associated homeostatic plasticity is unknown. METHODS Electrophysiology, Western blot, and behavioral analyses were used to quantify changes in hippocampal small conductance calcium-activated potassium (SK) channel function and expression using well-characterized in vitro and in vivo models of chronic alcohol exposure. RESULTS Chronic ethanol reduced apamin-sensitive SK currents in cornu ammonis 1 pyramidal neurons that were associated with a downregulation of surface SK2 channels. Blocking SK channels with apamin potentiated excitatory postsynaptic potentials in control but not ethanol-treated cornu ammonis 1 pyramidal neurons, suggesting that chronic ethanol disrupts the SK channel-NMDA receptor feedback loop. Alcohol reduced expression of SK2 channels and increased expression of NMDA receptors at synaptic sites in a mouse model. Positive modulation of SK function by 1-EBIO decreased alcohol withdrawal hyperexcitability and attenuated ethanol withdrawal neurotoxicity in hippocampus. The 1-EBIO also reduced seizure activity in mice undergoing withdrawal. CONCLUSIONS These results provide evidence that SK2 channels contribute to alcohol-associated adaptive plasticity of glutamatergic synapses and that positive modulation of SK channels reduces the severity of withdrawal-related hyperexcitability. Therefore, SK2 channels appear to be critical regulators of alcohol-associated plasticity and may be novel therapeutic targets for the treatment of addiction.
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Affiliation(s)
- Patrick J. Mulholland
- Department of Neurosciences, Medical University of South Carolina, 67 President Street, Charleston, SC, 29425
| | - Howard C. Becker
- Department of Psychiatry and VAMC, Medical University of South Carolina, 67 President Street, Charleston, SC, 29425
| | - John J. Woodward
- Department of Neurosciences, Medical University of South Carolina, 67 President Street, Charleston, SC, 29425
| | - L. Judson Chandler
- Department of Neurosciences, Medical University of South Carolina, 67 President Street, Charleston, SC, 29425
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60
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Grube S, Gerchen MF, Adamcio B, Pardo LA, Martin S, Malzahn D, Papiol S, Begemann M, Ribbe K, Friedrichs H, Radyushkin KA, Müller M, Benseler F, Riggert J, Falkai P, Bickeböller H, Nave KA, Brose N, Stühmer W, Ehrenreich H. A CAG repeat polymorphism of KCNN3 predicts SK3 channel function and cognitive performance in schizophrenia. EMBO Mol Med 2011; 3:309-19. [PMID: 21433290 PMCID: PMC3377084 DOI: 10.1002/emmm.201100135] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 02/24/2011] [Accepted: 02/25/2011] [Indexed: 12/11/2022] Open
Abstract
KCNN3, encoding the small conductance calcium-activated potassium channel SK3, harbours a polymorphic CAG repeat in the amino-terminal coding region with yet unproven function. Hypothesizing that KCNN3 genotypes do not influence susceptibility to schizophrenia but modify its phenotype, we explored their contribution to specific schizophrenic symptoms. Using the Göttingen Research Association for Schizophrenia (GRAS) data collection of schizophrenic patients (n = 1074), we performed a phenotype-based genetic association study (PGAS) of KCNN3. We show that long CAG repeats in the schizophrenic sample are specifically associated with better performance in higher cognitive tasks, comprising the capacity to discriminate, select and execute (p < 0.0001). Long repeats reduce SK3 channel function, as we demonstrate by patch-clamping of transfected HEK293 cells. In contrast, modelling the opposite in mice, i.e. KCNN3 overexpression/channel hyperfunction, leads to selective deficits in higher brain functions comparable to those influenced by SK3 conductance in humans. To conclude, KCNN3 genotypes modify cognitive performance, shown here in a large sample of schizophrenic patients. Reduction of SK3 function may constitute a pharmacological target to improve cognition in schizophrenia and other conditions with cognitive impairment.
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Affiliation(s)
- Sabrina Grube
- Divison of Clinical Neuroscience, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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61
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Electrostatic influences of charged inner pore residues on the conductance and gating of small conductance Ca2+ activated K+ channels. Proc Natl Acad Sci U S A 2011; 108:5946-53. [PMID: 21422289 DOI: 10.1073/pnas.1103090108] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
SK channels underlie important physiological functions by linking calcium signaling with neuronal excitability. Potassium currents through SK channels demonstrate inward rectification, which further reduces their small outward conductance. Although it has been generally attributed to block of outward current by intracellular divalent ions, we find that inward rectification is in fact an intrinsic property of SK channels independent of intracellular blockers. We identified three charged residues in the S6 transmembrane domain of SK channels near the inner mouth of the pore that collectively control the conductance and rectification through an electrostatic mechanism. Additionally, electrostatic contributions from these residues also play an important role in determining the intrinsic open probability of SK channels in the absence of Ca(2+), affecting the apparent Ca(2+) affinity for activation.
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62
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Hadi-Alijanvand H, Rouhani M, Proctor EA, Dokholyan NV, Moosavi-Movahedi AA. A folding pathway-dependent score to recognize membrane proteins. PLoS One 2011; 6:e16778. [PMID: 21390303 PMCID: PMC3046963 DOI: 10.1371/journal.pone.0016778] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2010] [Accepted: 12/29/2010] [Indexed: 12/11/2022] Open
Abstract
While various approaches exist to study protein localization, it is still a challenge to predict where proteins localize. Here, we consider a mechanistic viewpoint for membrane localization. Taking into account the steps for the folding pathway of α-helical membrane proteins and relating biophysical parameters to each of these steps, we create a score capable of predicting the propensity for membrane localization and call it FP(3)mem. This score is driven from the principal component analysis (PCA) of the biophysical parameters related to membrane localization. FP(3)mem allows us to rationalize the colocalization of a number of channel proteins with the Cav1.2 channel by their fewer propensities for membrane localization.
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Affiliation(s)
| | - Maryam Rouhani
- Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran
| | - Elizabeth A. Proctor
- Genetics Medicine, Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Nikolay V. Dokholyan
- Genetics Medicine, Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
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63
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Wersinger E, Fuchs PA. Modulation of hair cell efferents. Hear Res 2010; 279:1-12. [PMID: 21187136 DOI: 10.1016/j.heares.2010.12.018] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Revised: 12/10/2010] [Accepted: 12/20/2010] [Indexed: 02/01/2023]
Abstract
Outer hair cells (OHCs) amplify the sound-evoked motion of the basilar membrane to enhance acoustic sensitivity and frequency selectivity. Medial olivocochlear (MOC) efferents inhibit OHCs to reduce the sound-evoked response of cochlear afferent neurons. OHC inhibition occurs through the activation of postsynaptic α9α10 nicotinic receptors tightly coupled to calcium-dependent SK2 channels that hyperpolarize the hair cell. MOC neurons are cholinergic but a number of other neurotransmitters and neuromodulators have been proposed to participate in efferent transmission, with emerging evidence for both pre- and postsynaptic effects. Cochlear inhibition in vivo is maximized by repetitive activation of the efferents, reflecting facilitation and summation of transmitter release onto outer hair cells. This review summarizes recent studies on cellular and molecular mechanisms of cholinergic inhibition and the regulation of those molecular components, in particular the involvement of intracellular calcium. Facilitation at the efferent synapse is compared in a variety of animals, as well as other possible mechanisms of modulation of ACh release. These results suggest that short-term plasticity contributes to effective cholinergic inhibition of hair cells.
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Affiliation(s)
- Eric Wersinger
- The Center for Hearing and Balance, Department of Otolaryngology Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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64
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A small-conductance Ca2+-dependent K+ current regulates dopamine neuron activity: a combined approach of dynamic current clamping and intracellular imaging of calcium signals. Neuroreport 2010; 21:667-74. [PMID: 20508546 DOI: 10.1097/wnr.0b013e32833add56] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
To analyze the small-conductance calcium-dependent K current observed in dopaminergic neurons of the rat midbrain, we have developed a new dynamic current clamping method that incorporates recording of intracellular Ca levels. As reported earlier, blocking the small-conductance current with apamin shifted the firing modes of dopaminergic neurons and changed the firing rate and spike afterhyperpolarization. We modeled the kinetic properties of the current and assessed the model in a real-time computational system. Here, we show that the spike afterhyperpolarization is regulated by the small-conductance current, an effect that is observed in dopaminergic neurons. Thus, this current can effectively shape the autonomous firing patterns of dopaminergic neurons.
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The sigma agonist 1,3-di-o-tolyl-guanidine directly blocks SK channels in dopaminergic neurons and in cell lines. Eur J Pharmacol 2010; 641:23-8. [DOI: 10.1016/j.ejphar.2010.05.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 04/27/2010] [Accepted: 05/06/2010] [Indexed: 11/18/2022]
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66
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Oliveira MS, Skinner F, Arshadmansab MF, Garcia I, Mello CF, Knaus HG, Ermolinsky BS, Otalora LFP, Garrido-Sanabria ER. Altered expression and function of small-conductance (SK) Ca(2+)-activated K+ channels in pilocarpine-treated epileptic rats. Brain Res 2010; 1348:187-99. [PMID: 20553876 DOI: 10.1016/j.brainres.2010.05.095] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2009] [Revised: 05/28/2010] [Accepted: 05/30/2010] [Indexed: 01/09/2023]
Abstract
Small conductance calcium (Ca(2+)) activated SK channels are critical regulators of neuronal excitability in hippocampus. Accordingly, these channels are thought to play a key role in controlling neuronal activity in acute models of epilepsy. In this study, we investigate the expression and function of SK channels in the pilocarpine model of mesial temporal lobe epilepsy. For this purpose, protein expression was assessed using western blotting assays and gene expression was analyzed using TaqMan-based probes and the quantitative real-time polymerase chain reaction (qPCR) comparative method delta-delta cycle threshold ( big up tri, open big up tri, openCT) in samples extracted from control and epileptic rats. In addition, the effect of SK channel antagonist UCL1684 and agonist NS309 on CA1 evoked population spikes was studied in hippocampal slices. Western blotting analysis showed a significant reduction in the expression of SK1 and SK2 channels at 10days following status epilepticus (SE), but levels recovered at 1month and at more than 2months after SE. In contrast, a significant down-regulation of SK3 channels was detected after 10days of SE. Analysis of gene expression by qPCR revealed a significant reduction of transcripts for SK2 (Kcnn1) and SK3 (Kcnn3) channels as early as 10days following pilocarpine-induced SE and during the chronic phase of the pilocarpine model. Moreover, bath application of UCL1684 (100nM for 15min) induced a significant increase of the population spike amplitude and number of spikes in the hippocampal CA1 area of slices obtained control and chronic epileptic rats. This effect was obliterated by co-administration of UCL1684 with SK channel agonist NS309 (1microM). Application of NS309 failed to modify population spikes in the CA1 area of slices taken from control and epileptic rats. These data indicate an abnormal expression of SK channels and a possible dysfunction of these channels in experimental MTLE.
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Affiliation(s)
- Mauro S Oliveira
- Departamento de Fisiologia e Farmacologia, Centro de Ciências da Saúde, Universidade Federal de Santa Maria, RS, Brazil
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Luján R. Organisation of potassium channels on the neuronal surface. J Chem Neuroanat 2010; 40:1-20. [PMID: 20338235 DOI: 10.1016/j.jchemneu.2010.03.003] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2010] [Revised: 03/10/2010] [Accepted: 03/11/2010] [Indexed: 11/30/2022]
Abstract
Potassium channels are a family of ion channels that govern the intrinsic electrical properties of neurons in the brain. Molecular cloning has revealed over 100 genes encoding the pore-forming alpha subunits of potassium channels in mammals, making them the most diverse subset of ion channels. Multiplicity in this ion channel family is further generated through alternative splicing. The precise location of potassium channels along the dendro-somato-axonic surface of the neurons is an important factor in determining its functional impact. Today, it is widely accepted that potassium channels can be located at any subcellular compartment on the neuronal surface, at synaptic and extrasynaptic sites, from somata to dendritic shafts, dendritic spines, axons or axon terminals. However, they are not evenly distributed on the neuronal surface and depending on the potassium channel subtype, are instead concentrated at different compartments. This selective localization of ion channels to specific neuronal compartments has many different functional implications. One factor necessary to understand the role of potassium channels in neuronal function is to unravel their specialized distribution and subcellular localization within a cell, and this can only be achieved by electron microscopy. In this review, I summarize anatomical findings, describing their distribution in the central nervous system. The distinct regional, cellular and subcellular distribution of potassium channels in the brain will be discussed in view of their possible functional implications.
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Affiliation(s)
- Rafael Luján
- Departamento de Ciencias Médicas, Instituto de Investigación en Discapacidades Neurológicas (IDINE), Facultad de Medicina, Universidad de Castilla-La Mancha, Campus Biosanitario, C/Almansa 14, 02006 Albacete, Spain.
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Pugh PC, Jayakar SS, Margiotta JF. PACAP/PAC1R signaling modulates acetylcholine release at neuronal nicotinic synapses. Mol Cell Neurosci 2009; 43:244-57. [PMID: 19958833 DOI: 10.1016/j.mcn.2009.11.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2009] [Revised: 11/18/2009] [Accepted: 11/19/2009] [Indexed: 12/11/2022] Open
Abstract
Neuropeptides collaborate with conventional neurotransmitters to regulate synaptic output. Pituitary adenylate cyclase-activating polypeptide (PACAP) co-localizes with acetylcholine in presynaptic nerve terminals, is released by stimulation, and enhances nicotinic acetylcholine receptor- (nAChR-) mediated responses. Such findings implicate PACAP in modulating nicotinic neurotransmission, but relevant synaptic mechanisms have not been explored. We show here that PACAP acts via selective high-affinity G-protein coupled receptors (PAC(1)Rs) to enhance transmission at nicotinic synapses on parasympathetic ciliary ganglion (CG) neurons by rapidly and persistently increasing the frequency and amplitude of spontaneous, impulse-dependent nicotinic excitatory postsynaptic currents (sEPSCs). Of the canonical adenylate cyclase (AC) and phospholipase-C (PLC) transduction cascades stimulated by PACAP/PAC(1)R signaling, only AC-generated signals are critical for synaptic modulation since the increases in sEPSC frequency and amplitude were mimicked by 8-Bromo-cAMP, blocked by inhibiting AC or cAMP-dependent protein kinase (PKA), and unaffected by inhibiting PLC. Despite its ability to increase agonist-induced nAChR currents, PACAP failed to influence nAChR-mediated impulse-independent miniature EPSC amplitudes (quantal size). Instead, evoked transmission assays reveal that PACAP/PAC(1)R signaling increased quantal content, indicating that it modulates synaptic function by increasing vesicular ACh release from presynaptic terminals. Lastly, signals generated by the retrograde messenger, nitric oxide- (NO-) are critical for the synaptic modulation since the PACAP-induced increases in spontaneous EPSC frequency, amplitude and quantal content were mimicked by NO donor and absent after inhibiting NO synthase (NOS). These results indicate that PACAP/PAC(1)R activation recruits AC-dependent signaling that stimulates NOS to increase NO production and control presynaptic transmitter output at neuronal nicotinic synapses.
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Affiliation(s)
- Phyllis C Pugh
- University of Toledo College of Medicine, Department of Neurosciences, Toledo, OH 43614-5804, USA
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