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Ramis R, Ballesteros ÓR, Muguruza-Montero A, M-Alicante S, Núñez E, Villarroel Á, Leonardo A, Bergara A. Molecular dynamics simulations of the calmodulin-induced α-helix in the SK2 calcium-gated potassium ion channel. J Biol Chem 2022; 299:102850. [PMID: 36587765 PMCID: PMC9874072 DOI: 10.1016/j.jbc.2022.102850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Revised: 12/21/2022] [Accepted: 12/23/2022] [Indexed: 12/30/2022] Open
Abstract
The family of small-conductance Ca2+-activated potassium ion channels (SK channels) is composed of four members (SK1, SK2, SK3, and SK4) involved in neuron-firing regulation. The gating of these channels depends on the intracellular Ca2+ concentration, and their sensitivity to this ion is provided by calmodulin (CaM). This protein binds to a specific region in SK channels known as the calmodulin-binding domain (CaMBD), an event which is essential for their gating. While CaMBDs are typically disordered in the absence of CaM, the SK2 channel subtype displays a small prefolded α-helical region in its CaMBD even if CaM is not present. This small helix is known to turn into a full α-helix upon CaM binding, although the molecular-level details for this conversion are not fully understood yet. In this work, we offer new insights on this physiologically relevant process by means of enhanced sampling, atomistic Hamiltonian replica exchange molecular dynamics simulations, providing a more detailed understanding of CaM binding to this target. Our results show that CaM is necessary for inducing a full α-helix along the SK2 CaMBD through hydrophobic interactions with V426 and L427. However, it is also necessary that W431 does not compete for these interactions; the role of the small prefolded α-helix in the SK2 CaMBD would be to stabilize W431 so that this is the case. In conclusion, our findings provide further insight into a key interaction between CaM and SK channels that is important for channel sensitivity to Ca2+.
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Affiliation(s)
- Rafael Ramis
- Donostia International Physics Center, Donostia, Spain; Departamento de Física, Universidad del País Vasco, UPV/EHU, Leioa, Spain.
| | - Óscar R. Ballesteros
- Departamento de Física, Universidad del País Vasco, UPV/EHU, Leioa, Spain,Centro de Física de Materiales CFM, CSIC-UPV/EHU, Donostia, Spain
| | | | - Sara M-Alicante
- Departamento de Física, Universidad del País Vasco, UPV/EHU, Leioa, Spain,Instituto Biofisika, CSIC-UPV/EHU, Leioa, Spain
| | - Eider Núñez
- Departamento de Física, Universidad del País Vasco, UPV/EHU, Leioa, Spain,Instituto Biofisika, CSIC-UPV/EHU, Leioa, Spain
| | | | - Aritz Leonardo
- Donostia International Physics Center, Donostia, Spain,Departamento de Física, Universidad del País Vasco, UPV/EHU, Leioa, Spain
| | - Aitor Bergara
- Donostia International Physics Center, Donostia, Spain,Departamento de Física, Universidad del País Vasco, UPV/EHU, Leioa, Spain,Centro de Física de Materiales CFM, CSIC-UPV/EHU, Donostia, Spain
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2
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A Neuro-hormonal Circuit for Paternal Behavior Controlled by a Hypothalamic Network Oscillation. Cell 2020; 182:960-975.e15. [PMID: 32763155 PMCID: PMC7445434 DOI: 10.1016/j.cell.2020.07.007] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 10/21/2019] [Accepted: 07/09/2020] [Indexed: 02/08/2023]
Abstract
Parental behavior is pervasive throughout the animal kingdom and essential for species survival. However, the relative contribution of the father to offspring care differs markedly across animals, even between related species. The mechanisms that organize and control paternal behavior remain poorly understood. Using Sprague-Dawley rats and C57BL/6 mice, two species at opposite ends of the paternal spectrum, we identified that distinct electrical oscillation patterns in neuroendocrine dopamine neurons link to a chain of low dopamine release, high circulating prolactin, prolactin receptor-dependent activation of medial preoptic area galanin neurons, and paternal care behavior in male mice. In rats, the same parameters exhibit inverse profiles. Optogenetic manipulation of these rhythms in mice dramatically shifted serum prolactin and paternal behavior, whereas injecting prolactin into non-paternal rat sires triggered expression of parental care. These findings identify a frequency-tuned brain-endocrine-brain circuit that can act as a gain control system determining a species’ parental strategy. Species-specific hypothalamic dopamine neuron rhythms yield distinct prolactin release Serum prolactin primes the “parental” neural circuit for pup care during fatherhood Optogenetic control of TIDA frequency tunes prolactin and paternal behavior Prolactin receptors in the MPOA are required for paternal behavior
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3
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Cui ED, Strowbridge BW. Selective attenuation of Ether-a-go-go related K + currents by endogenous acetylcholine reduces spike-frequency adaptation and network correlation. eLife 2019; 8:44954. [PMID: 31032798 PMCID: PMC6488300 DOI: 10.7554/elife.44954] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 04/11/2019] [Indexed: 12/21/2022] Open
Abstract
Most neurons do not simply convert inputs into firing rates. Instead, moment-to-moment firing rates reflect interactions between synaptic inputs and intrinsic currents. Few studies investigated how intrinsic currents function together to modulate output discharges and which of the currents attenuated by synthetic cholinergic ligands are actually modulated by endogenous acetylcholine (ACh). In this study we optogenetically stimulated cholinergic fibers in rat neocortex and find that ACh enhances excitability by reducing Ether-à-go-go Related Gene (ERG) K+ current. We find ERG mediates the late phase of spike-frequency adaptation in pyramidal cells and is recruited later than both SK and M currents. Attenuation of ERG during coincident depolarization and ACh release leads to reduced late phase spike-frequency adaptation and persistent firing. In neuronal ensembles, attenuating ERG enhanced signal-to-noise ratios and reduced signal correlation, suggesting that these two hallmarks of cholinergic function in vivo may result from modulation of intrinsic properties.
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Affiliation(s)
- Edward D Cui
- Department of Neurosciences, Case Western Reserve University, Cleveland, United States
| | - Ben W Strowbridge
- Department of Neurosciences, Case Western Reserve University, Cleveland, United States
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4
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Cho LTY, Alexandrou AJ, Torella R, Knafels J, Hobbs J, Taylor T, Loucif A, Konopacka A, Bell S, Stevens EB, Pandit J, Horst R, Withka JM, Pryde DC, Liu S, Young GT. An Intracellular Allosteric Modulator Binding Pocket in SK2 Ion Channels Is Shared by Multiple Chemotypes. Structure 2018; 26:533-544.e3. [PMID: 29576321 DOI: 10.1016/j.str.2018.02.017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Revised: 12/03/2017] [Accepted: 02/23/2018] [Indexed: 01/22/2023]
Abstract
Small conductance potassium (SK) ion channels define neuronal firing rates by conducting the after-hyperpolarization current. They are key targets in developing therapies where neuronal firing rates are dysfunctional, such as in epilepsy, Parkinson's, and amyotrophic lateral sclerosis (ALS). Here, we characterize a binding pocket situated at the intracellular interface of SK2 and calmodulin, which we show to be shared by multiple small-molecule chemotypes. Crystallization of this complex revealed that riluzole (approved for ALS) and an analog of the anti-ataxic agent (4-chloro-phenyl)-[2-(3,5-dimethyl-pyrazol-1-yl)-pyrimidin-4-yl]-amine (CyPPA) bind to and allosterically modulate via this site. Solution-state nuclear magnetic resonance demonstrates that riluzole, NS309, and CyPPA analogs bind at this bipartite pocket. We demonstrate, by patch-clamp electrophysiology, that both classes of ligand interact with overlapping but distinct residues within this pocket. These data define a clinically important site, laying the foundations for further studies of the mechanism of action of riluzole and related molecules.
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Affiliation(s)
- Lily T-Y Cho
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Aristos J Alexandrou
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Rubben Torella
- Pfizer Worldwide Medicinal Chemistry, Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - John Knafels
- Pfizer Structural Biology and Biophysics, Groton, Eastern Point Road, Groton, CT 06340, USA
| | - Jake Hobbs
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Toni Taylor
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Alex Loucif
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Agnieszka Konopacka
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Sigourney Bell
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Edward B Stevens
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Jay Pandit
- Pfizer Structural Biology and Biophysics, Groton, Eastern Point Road, Groton, CT 06340, USA
| | - Reto Horst
- Pfizer Structural Biology and Biophysics, Groton, Eastern Point Road, Groton, CT 06340, USA
| | - Jane M Withka
- Pfizer Structural Biology and Biophysics, Groton, Eastern Point Road, Groton, CT 06340, USA
| | - David C Pryde
- Pfizer Worldwide Medicinal Chemistry, Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK
| | - Shenping Liu
- Pfizer Structural Biology and Biophysics, Groton, Eastern Point Road, Groton, CT 06340, USA.
| | - Gareth T Young
- Pfizer Neuroscience and Pain Research Unit, Granta Park, Great Abington, Cambridge CB21 6GS, UK.
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5
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Paeger L, Pippow A, Hess S, Paehler M, Klein AC, Husch A, Pouzat C, Brüning JC, Kloppenburg P. Energy imbalance alters Ca 2+ handling and excitability of POMC neurons. eLife 2017; 6. [PMID: 28762947 PMCID: PMC5538824 DOI: 10.7554/elife.25641] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2017] [Accepted: 06/29/2017] [Indexed: 01/16/2023] Open
Abstract
Satiety-signaling, pro-opiomelanocortin (POMC)-expressing neurons in the arcuate nucleus of the hypothalamus play a pivotal role in the regulation of energy homeostasis. Recent studies reported altered mitochondrial dynamics and decreased mitochondria- endoplasmic reticulum contacts in POMC neurons during diet-induced obesity. Since mitochondria play a crucial role in Ca2+ signaling, we investigated whether obesity alters Ca2+ handling of these neurons in mice. In diet-induced obesity, cellular Ca2+ handling properties including mitochondrial Ca2+ uptake capacity are impaired, and an increased resting level of free intracellular Ca2+ is accompanied by a marked decrease in neuronal excitability. Experimentally increasing or decreasing intracellular Ca2+ concentrations reproduced electrophysiological properties observed in diet-induced obesity. Taken together, we provide the first direct evidence for a diet-dependent deterioration of Ca2+ homeostasis in POMC neurons during obesity development resulting in impaired function of these critical energy homeostasis-regulating neurons. DOI:http://dx.doi.org/10.7554/eLife.25641.001
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Affiliation(s)
- Lars Paeger
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
| | - Andreas Pippow
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
| | - Simon Hess
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
| | - Moritz Paehler
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
| | - Andreas C Klein
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
| | - Andreas Husch
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
| | - Christophe Pouzat
- MAP5 - Mathématiques Appliquées à Paris 5, CNRS UMR 8145, Paris, France
| | - Jens C Brüning
- Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany.,Department of Mouse Genetics and Metabolism, Institute for Genetics, Center of Molecular Medicine Cologne, Center for Endocrinology, Diabetes and Preventive Medicine, University Hospital of Cologne, Cologne, Germany.,Max Planck Institute for Metabolism Research, Cologne, Germany
| | - Peter Kloppenburg
- Biocenter, Institute for Zoology, University of Cologne, Cologne, Germany.,Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, University of Cologne, Cologne, Germany
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6
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Nenov MN, Tempia F, Denner L, Dineley KT, Laezza F. Impaired firing properties of dentate granule neurons in an Alzheimer's disease animal model are rescued by PPARγ agonism. J Neurophysiol 2014; 113:1712-26. [PMID: 25540218 PMCID: PMC4359997 DOI: 10.1152/jn.00419.2014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Early cognitive impairment in Alzheimer's disease (AD) correlates with medial temporal lobe dysfunction, including two areas essential for memory formation: the entorhinal cortex and dentate gyrus (DG). In the Tg2576 animal model for AD amyloidosis, activation of the peroxisome proliferator-activated receptor-gamma (PPARγ) with rosiglitazone (RSG) ameliorates hippocampus-dependent cognitive impairment and restores aberrant synaptic activity at the entorhinal cortex to DG granule neuron inputs. It is unknown, however, whether intrinsic firing properties of DG granule neurons in these animals are affected by amyloid-β pathology and if they are sensitive to RSG treatment. Here, we report that granule neurons from 9-mo-old wild-type and Tg2576 animals can be segregated into two cell types with distinct firing properties and input resistance that correlate with less mature type I and more mature type II neurons. The DG type I cell population was greater than type II in wild-type littermates. In the Tg2576 animals, the type I and type II cell populations were nearly equal but could be restored to wild-type levels through cognitive enhancement with RSG. Furthermore, Tg2576 cell firing frequency and spike after depolarization were decreased in type I and increased in type II cells, both of which could also be restored to wild-type levels upon RSG treatment. That these parameters were restored by PPARγ activation emphasizes the therapeutic value of RSG against early AD cognitive impairment.
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Affiliation(s)
- Miroslav N Nenov
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas
| | - Filippo Tempia
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas
| | - Larry Denner
- Department of Internal Medicine, The University of Texas Medical Branch, Galveston, Texas; Center for Addiction Research, The University of Texas Medical Branch, Galveston, Texas; Mitchell Center for Neurodegenerative Diseases, The University of Texas Medical Branch, Galveston, Texas; and
| | - Kelly T Dineley
- Department of Neurology, The University of Texas Medical Branch, Galveston, Texas; Center for Addiction Research, The University of Texas Medical Branch, Galveston, Texas; Mitchell Center for Neurodegenerative Diseases, The University of Texas Medical Branch, Galveston, Texas; and
| | - Fernanda Laezza
- Department of Pharmacology and Toxicology, The University of Texas Medical Branch, Galveston, Texas; Center for Addiction Research, The University of Texas Medical Branch, Galveston, Texas; Mitchell Center for Neurodegenerative Diseases, The University of Texas Medical Branch, Galveston, Texas; and Center for Biomedical Engineering, The University of Texas Medical Branch, Galveston, Texas
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7
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Voisin AN, Mouginot D, Drolet G. Multiple episodes of sodium depletion in the rat: a remodeling of the electrical properties of median preoptic nucleus neurons. Eur J Neurosci 2013; 38:2730-41. [DOI: 10.1111/ejn.12273] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 05/06/2013] [Accepted: 05/08/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Aurore N. Voisin
- Axe Neurosciences du Centre de recherche du CHU and Université Laval; P-09800, 2705 Laurier; Québec; QC; G1V4G2; Canada
| | - Didier Mouginot
- Axe Neurosciences du Centre de recherche du CHU and Université Laval; P-09800, 2705 Laurier; Québec; QC; G1V4G2; Canada
| | - Guy Drolet
- Axe Neurosciences du Centre de recherche du CHU and Université Laval; P-09800, 2705 Laurier; Québec; QC; G1V4G2; Canada
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8
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Voisin AN, Drolet G, Mouginot D. Intrinsic properties of the sodium sensor neurons in the rat median preoptic nucleus. Am J Physiol Regul Integr Comp Physiol 2012; 303:R834-42. [PMID: 22874426 DOI: 10.1152/ajpregu.00260.2012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The essential role of the median preoptic nucleus (MnPO) in the integration of chemosensory information associated with the hydromineral state of the rat relies on the presence of a unique population of sodium (Na+) sensor neurons. Little is known about the intrinsic properties of these neurons; therefore, we used whole cell recordings in acute brain slices to determine the electrical fingerprints of this specific neural population of rat MnPO. The data collected from a large sample of neurons (115) indicated that the Na+ sensor neurons represent a majority of the MnPO neurons in situ (83%). These neurons displayed great diversity in both firing patterns induced by transient depolarizing current steps and rectifying properties activated by hyperpolarizing current steps. This diversity of electrical properties was also present in non-Na+ sensor neurons. Subpopulations of Na+ sensor neurons could be distinguished, however, from the non-Na+ sensor neurons. The firing frequency was higher in Na+ sensor neurons, showing irregular spike discharges, and the amplitude of the time-dependent rectification was weaker in the Na+ sensor neurons than in non-Na+ sensor neurons. The diversity among the electrical properties of the MnPO neurons contrasts with the relative function homogeneity (Na+ sensing). However, this diversity might be correlated with a variety of direct synaptic connections linking the MnPO to different brain areas involved in various aspects of the restoration and conservation of the body fluid homeostasis.
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Affiliation(s)
- Aurore N Voisin
- Axe Neurosciences du Centre de recherche du CHUQ, Université Laval, Québec, QC, Canada
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9
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Kaffashian M, Shabani M, Goudarzi I, Behzadi G, Zali A, Janahmadi M. Profound alterations in the intrinsic excitability of cerebellar Purkinje neurons following neurotoxin 3-acetylpyridine (3-AP)-induced ataxia in rat: new insights into the role of small conductance K+ channels. Physiol Res 2010; 60:355-65. [PMID: 21114365 DOI: 10.33549/physiolres.932032] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Alterations in the intrinsic properties of Purkinje cells (PCs) may contribute to the abnormal motor performance observed in ataxic rats. To investigate whether such changes in the intrinsic neuronal excitability could be attributed to the role of Ca(2+)-activated K(+) channels (K(Ca)), whole cell current clamp recordings were made from PCs in cerebellar slices of control and ataxic rats. 3-AP induced profound alterations in the intrinsic properties of PCs, as evidenced by a significant increase in both the membrane input resistance and the initial discharge frequency, along with the disruption of the firing regularity. In control PCs, the blockade of small conductance K(Ca) channels by UCL1684 resulted in a significant increase in the membrane input resistance, action potential (AP) half-width, time to peak of the AP and initial discharge frequency. SK channel blockade also significantly decreased the neuronal discharge regularity, the peak amplitude of the AP, the amplitude of the afterhyperpolarization and the spike frequency adaptation ratio. In contrast, in ataxic rats, both the firing regularity and the initial firing frequency were significantly increased by the blockade of SK channels. In conclusion, ataxia may arise from alterations in the functional contribution of SK channels, to the intrinsic properties of PCs.
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Affiliation(s)
- M Kaffashian
- Neuroscience Research Centre and Department of Physiology, Medical School, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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10
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Vatanparast J, Janahmadi M. Contribution of apamin-sensitive SK channels to the firing precision but not to the slow afterhyperpolarization and spike frequency adaptation in snail neurons. Brain Res 2008; 1255:57-66. [PMID: 19100724 DOI: 10.1016/j.brainres.2008.12.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2008] [Revised: 12/01/2008] [Accepted: 12/02/2008] [Indexed: 10/21/2022]
Abstract
Apamin-sensitive small conductance Ca(2+)-dependent K(+)(SK) channels are generally accepted as responsible for the medium afterhyperpolarization (mAHP) after single or train of action potentials. Here, we examined the functional involvement of these channels in the firing precision, post train AHP and spike frequency adaptation (SFA) in neurons of snail Caucasotachea atrolabiata. Apamin, a selective SK channel antagonist, reduced the duration of single-spike AHP and disrupted the spontaneous rhythmic activity. High frequency trains of evoked action potentials showed a time-dependent decrease in the action potential discharge rate (spike frequency adaptation) and followed by a prominent post stimulus inhibitory period (PSIP) as a marker of slow AHP (sAHP). Neither sAHP nor SFA was attenuated by apamin, suggesting that apamin-sensitive SK channels can strongly affect the rhythmicity, but are probably not involved in the SFA and sAHP. Nifedipine, antagonist of L-type Ca(2+) channels, decreased the firing frequency and neuronal rhythmicity. When PSIP was normalized to the background interspike interval, a suppressing effect of nifedipine on PSIP was also observed. Intracellular iontophoretic injection of BAPTA, a potent Ca(2+) chelator, dramatically suppressed PSIP that confirms the intracellular Ca(2+) dependence of the sAHP, but had no discernable effect on the SFA. During train-evoked activity a reduction in the action potential overshoot and maximum depolarization rate was also observed, along with a decrease in the firing frequency, while the action potential threshold increased, which indicated that Na(+) channels, rather than Ca(2+)-dependent K(+) channels, are involved in the SFA.
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Affiliation(s)
- Jafar Vatanparast
- Department of Biology, College of Sciences, Shiraz University, Adabiat Intersection, Shiraz 71454, Iran.
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11
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Brenner R, Chen QH, Vilaythong A, Toney GM, Noebels JL, Aldrich RW. BK channel beta4 subunit reduces dentate gyrus excitability and protects against temporal lobe seizures. Nat Neurosci 2005; 8:1752-9. [PMID: 16261134 DOI: 10.1038/nn1573] [Citation(s) in RCA: 274] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Accepted: 09/23/2005] [Indexed: 11/08/2022]
Abstract
Synaptic inhibition within the hippocampus dentate gyrus serves a 'low-pass filtering' function that protects against hyperexcitability that leads to temporal lobe seizures. Here we demonstrate that calcium-activated potassium (BK) channel accessory beta4 subunits serve as key regulators of intrinsic firing properties that contribute to the low-pass filtering function of dentate granule cells. Notably, a critical beta4 subunit function is to preclude BK channels from contributing to membrane repolarization and thereby broaden action potentials. Longer-duration action potentials secondarily recruit SK channels, leading to greater spike frequency adaptation and reduced firing rates. In contrast, granule cells from beta4 knockout mice show a gain-of-function for BK channels that sharpens action potentials and supports higher firing rates. Consistent with breakdown of the dentate filter, beta4 knockouts show distinctive seizures emanating from the temporal cortex, demonstrating a unique nonsynaptic mechanism for gate control of hippocampal synchronization leading to temporal lobe epilepsy.
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Affiliation(s)
- Robert Brenner
- Department of Physiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229, USA
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12
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Liu X, Chen D, Xie L, Zhang R. Effect of honey bee venom on proliferation of K1735M2 mouse melanoma cells in-vitro and growth of murine B16 melanomas in-vivo. J Pharm Pharmacol 2002; 54:1083-9. [PMID: 12195822 DOI: 10.1211/002235702320266235] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Bee venom has been reported to exhibit antitumour activity in-vitro and in-vivo. Apoptosis, necrosis and lysis of tumour cells were suggested as possible mechanisms by which bee venom inhibited tumour growth. The aim of this study was to investigate potential mechanisms by which bee venom inhibits K1735M2 mouse melanoma cells in-vitro and B16 melanoma, a transplantable solid melanoma in C57BL/6 mice, in-vivo. The proliferation of K1735M2 cells in-vitro was inhibited by bee venom in a concentration- and time-dependent manner. The inhibition was indicated by the arrest of the cell cycle at the G1 stage, as detected by flow cytometric measurements. The bee venom induced apoptosis-like cell death as identified by histological observations and by DNA fragmentation. In the in-vivo experiments, the bee venom (1.0, 3.0, 9.0 mg kg-1 of body weight, on days 1-12) was injected intraperitoneally into mice 24 h after the mice were inoculated with B16 cells. Inhibition of the solid tumour was observed. Apoptosis of the K1735M2 cells was suggested as the possible mechanism by which bee venom inhibited cell proliferation and induced K1735M2 cell differentiation in-vitro. The in-vivo experiment indicated that bee venom could be used as a chemotherapeutic agent against malignant tumours.
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Affiliation(s)
- Xing Liu
- Department of Biological Science and Biotechnology, Tsinghua University, Beijing 100084, P.R. China
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Abstract
Individual brainstem neurons involved in vestibular reflexes respond to identical head movements with a wide range of firing responses. This diversity of firing dynamics has been commonly assumed to arise from differences in the types of vestibular nerve inputs to vestibular nucleus neurons. In this study we show that, independent of the nature of inputs, the intrinsic membrane properties of neurons in the medial vestibular nucleus substantially influence firing response dynamics. Hyperpolarizing and depolarizing inputs evoked a markedly heterogenous range of firing responses. Strong postinhibitory rebound firing (PRF) was associated with strong firing rate adaptation (FRA) and occurred preferentially in large multipolar neurons. In response to sinusoidally modulated input current, these neurons showed a pronounced phase lead with respect to neurons lacking strong PRF and FRA. A combination of the hyperpolarization-activated H current and slow potassium currents contributed to PRF, whereas FRA was predominantly mediated by slow potassium currents. An integrate-and-fire-type model, which simulated FRA and PRF, reproduced the phase lead observed in large neurons and showed that adaptation currents were primarily responsible for variations in response phase. We conclude that the heterogeneity of firing dynamics observed in response to head movements in intact animals reflects intrinsic as well as circuit properties.
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14
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Biomedical vignette. J Biomed Sci 1999. [DOI: 10.1007/bf02253666] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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