201
|
Waszkielewicz AM, Gunia A, Szkaradek N, Słoczyńska K, Krupińska S, Marona H. Ion channels as drug targets in central nervous system disorders. Curr Med Chem 2013; 20:1241-85. [PMID: 23409712 PMCID: PMC3706965 DOI: 10.2174/0929867311320100005] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Revised: 01/14/2013] [Accepted: 01/18/2013] [Indexed: 12/27/2022]
Abstract
Ion channel targeted drugs have always been related with either the central nervous system (CNS), the peripheral nervous system, or the cardiovascular system. Within the CNS, basic indications of drugs are: sleep disorders, anxiety, epilepsy, pain, etc. However, traditional channel blockers have multiple adverse events, mainly due to low specificity of mechanism of action. Lately, novel ion channel subtypes have been discovered, which gives premises to drug discovery process led towards specific channel subtypes. An example is Na(+) channels, whose subtypes 1.3 and 1.7-1.9 are responsible for pain, and 1.1 and 1.2 - for epilepsy. Moreover, new drug candidates have been recognized. This review is focusing on ion channels subtypes, which play a significant role in current drug discovery and development process. The knowledge on channel subtypes has developed rapidly, giving new nomenclatures of ion channels. For example, Ca(2+)s channels are not any more divided to T, L, N, P/Q, and R, but they are described as Ca(v)1.1-Ca(v)3.3, with even newer nomenclature α1A-α1I and α1S. Moreover, new channels such as P2X1-P2X7, as well as TRPA1-TRPV1 have been discovered, giving premises for new types of analgesic drugs.
Collapse
Affiliation(s)
- A M Waszkielewicz
- Department of Bioorganic Chemistry, Chair of Organic Chemistry, Faculty of Pharmacy, Jagiellonian University Medical College, 9 Medyczna Street, 30-688 Krakow, Poland.
| | | | | | | | | | | |
Collapse
|
202
|
Albertazzi L, Storti B, Brondi M, Sulis Sato S, Ratto GM, Signore G, Beltram F. Synthesis, cellular delivery and in vivo application of dendrimer-based pH sensors. J Vis Exp 2013. [PMID: 24056638 DOI: 10.3791/50545] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The development of fluorescent indicators represented a revolution for life sciences. Genetically encoded and synthetic fluorophores with sensing abilities allowed the visualization of biologically relevant species with high spatial and temporal resolution. Synthetic dyes are of particular interest thanks to their high tunability and the wide range of measureable analytes. However, these molecules suffer several limitations related to small molecule behavior (poor solubility, difficulties in targeting, often no ratiometric imaging allowed). In this work we introduce the development of dendrimer-based sensors and present a procedure for pH measurement in vitro, in living cells and in vivo. We choose dendrimers as ideal platform for our sensors for their many desirable properties (monodispersity, tunable properties, multivalency) that made them a widely used scaffold for several biomedical devices. The conjugation of fluorescent pH indicators to the dendrimer scaffold led to an enhancement of their sensing performances. In particular dendrimers exhibit reduced cell leakage, improved intracellular targeting and allow ratiometric measurements. These novel sensors were successfully employed to measure pH in living HeLa cells and in vivo in mouse brain.
Collapse
Affiliation(s)
- Lorenzo Albertazzi
- Institute for Complex Molecular Systems & Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology & NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR
| | | | | | | | | | | | | |
Collapse
|
203
|
Abstract
Why do neurons sense extracellular acid? In large part, this question has driven increasing investigation on acid-sensing ion channels (ASICs) in the CNS and the peripheral nervous system for the past two decades. Significant progress has been made in understanding the structure and function of ASICs at the molecular level. Studies aimed at clarifying their physiological importance have suggested roles for ASICs in pain, neurological and psychiatric disease. This Review highlights recent findings linking these channels to physiology and disease. In addition, it discusses some of the implications for therapy and points out questions that remain unanswered.
Collapse
|
204
|
Yin T, Lindley TE, Albert GW, Ahmed R, Schmeiser PB, Grady MS, Howard MA, Welsh MJ. Loss of Acid sensing ion channel-1a and bicarbonate administration attenuate the severity of traumatic brain injury. PLoS One 2013; 8:e72379. [PMID: 23991103 PMCID: PMC3753246 DOI: 10.1371/journal.pone.0072379] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Accepted: 07/09/2013] [Indexed: 12/30/2022] Open
Abstract
Traumatic brain injury (TBI) is a common cause of morbidity and mortality in people of all ages. Following the acute mechanical insult, TBI evolves over the ensuing minutes and days. Understanding the secondary factors that contribute to TBI might suggest therapeutic strategies to reduce the long-term consequences of brain trauma. To assess secondary factors that contribute to TBI, we studied a lateral fluid percussion injury (FPI) model in mice. Following FPI, the brain cortex became acidic, consistent with data from humans following brain trauma. Administering HCO3− after FPI prevented the acidosis and reduced the extent of neurodegeneration. Because acidosis can activate acid sensing ion channels (ASICs), we also studied ASIC1a−/− mice and found reduced neurodegeneration after FPI. Both HCO3− administration and loss of ASIC1a also reduced functional deficits caused by FPI. These results suggest that FPI induces cerebral acidosis that activates ASIC channels and contributes to secondary injury in TBI. They also suggest a therapeutic strategy to attenuate the adverse consequences of TBI.
Collapse
Affiliation(s)
- Terry Yin
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Timothy E. Lindley
- Department of Neurosurgery, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Gregory W. Albert
- Department of Neurosurgery, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Raheel Ahmed
- Department of Neurosurgery, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Peter B. Schmeiser
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - M. Sean Grady
- Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Matthew A. Howard
- Department of Neurosurgery, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
| | - Michael J. Welsh
- Department of Internal Medicine, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Department of Neurosurgery, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- Howard Hughes Medical Institute, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
| |
Collapse
|
205
|
Frey EN, Pavlovicz RE, Wegman CJ, Li C, Askwith CC. Conformational changes in the lower palm domain of ASIC1a contribute to desensitization and RFamide modulation. PLoS One 2013; 8:e71733. [PMID: 23977127 PMCID: PMC3743763 DOI: 10.1371/journal.pone.0071733] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 07/08/2013] [Indexed: 12/12/2022] Open
Abstract
Acid-sensing ion channel 1a (ASIC1a) is a proton-gated cation channel that contributes to fear and pain as well as neuronal damage following persistent cerebral acidosis. Neuropeptides can affect acid-induced neuronal injury by altering ASIC1a inactivation and/or steady-state desensitization. Yet, exactly how ASIC1a inactivation and desensitization occur or are modulated by peptides is not completely understood. We found that regions of the extracellular palm domain and the β11-12 linker are important for inactivation and steady-state desensitization of ASIC1a. The single amino acid substitutions L280C and L415C dramatically enhanced the rate of inactivation and altered the pH-dependence of steady-state desensitization. Further, the use of methanethiosulfonate (MTS) reagents suggests that the lower palm region (L280C) undergoes a conformational change when ASIC1a transitions from closed to desensitized. We determined that L280C also displays an altered response to the RFamide peptide, FRRFamide. Further, the presence of FRRFamide limited MTS modification of L280C. Together, these results indicate a potential role of the lower palm domain in peptide modulation and suggest RFamide-related peptides promote conformational changes within this region. These data provide empirical support for the idea that L280, and likely this region of the central vestibule, is intimately involved in channel inactivation and desensitization.
Collapse
Affiliation(s)
- Erin N. Frey
- Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, Ohio, United States of America
- Biomedical Sciences Graduate Program, The Ohio State University, Columbus, Ohio, United States of America
| | - Ryan E. Pavlovicz
- Biophysics Graduate Program, The Ohio State University, Columbus, Ohio, United States of America
| | - Clem John Wegman
- Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, Ohio, United States of America
| | - Chenglong Li
- Biophysics Graduate Program, The Ohio State University, Columbus, Ohio, United States of America
- Division of Medicinal Chemistry, College of Pharmacy, The Ohio State University, Columbus, Ohio, United States of America
| | - Candice C. Askwith
- Department of Neuroscience, Wexner Medical Center, The Ohio State University, Columbus, Ohio, United States of America
- * E-mail:
| |
Collapse
|
206
|
Du BL, Zeng CG, Zhang W, Quan DP, Ling EA, Zeng YS. A comparative study of gelatin sponge scaffolds and PLGA scaffolds transplanted to completely transected spinal cord of rat. J Biomed Mater Res A 2013; 102:1715-25. [PMID: 23776140 DOI: 10.1002/jbm.a.34835] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Revised: 05/31/2013] [Accepted: 06/05/2013] [Indexed: 11/09/2022]
Abstract
This study sought to investigate whether gelatin sponge (GS) scaffold would produce less acidic medium in injured spinal cord, as compared with poly(lactic-co-glycolic acid) (PLGA) scaffold, to determine which of the two scaffolds as the biomaterial is more suitable for transplantation into spinal cord. GS scaffold or PLGA scaffold was transplanted into a transected spinal cord in this study. Two months after transplantation of scaffolds, acid sensing ion channel 1a (ASIC1a) positive cells expressing microtubule associated protein 2 (Map2) were observed as well as expressing adenomatous polyposis coli (APC) in spinal cord. GFAP positive cells were distributed at the rostral and caudal of the injury/graft area in the GS and PLGA groups. Western blot showed ASIC1a and GFAP expression of injured spinal cord was downregulated in the GS group. The number of CD68 positive cells was fewer and NF nerve fibers were more in the GS group. Nissl staining and cell counting showed that the number of survival neurons was comparable between the GS and PLGA groups in the pyramidal layer of sensorimotor cortex and the red nucleus of midbrain. However, in the Clarke's nucleus at L1 spinal segment, the surviving neurons in the GS group were more numerous than that in the PLGA group. H&E staining showed that the tissue cavities in the GS group were smaller in size than that in the PLGA group. The results suggest that GS scaffold is more suitable for transplantation to promote the recovery of spinal cord injury compared with PLGA scaffold.
Collapse
Affiliation(s)
- Bao-ling Du
- Division of Neuroscience, Department of Histology and Embryology, Zhongshan School of Medicine, Sun Yat-sen University, Guangzhou, Guangdong, 510080, China
| | | | | | | | | | | |
Collapse
|
207
|
Leng T, Lin J, Cottrell JE, Xiong ZG. Subunit and frequency-dependent inhibition of acid sensing ion channels by local anesthetic tetracaine. Mol Pain 2013; 9:27. [PMID: 23758830 PMCID: PMC3695766 DOI: 10.1186/1744-8069-9-27] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 06/05/2013] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Extracellular acidosis is a prominent feature of multiple pathological conditions, correlating with pain sensation. Acid-sensing ion channels (ASICs), a family of proton-gated cation channels, are distributed throughout the central and peripheral nervous systems. Activation of ASICs, particularly ASIC3 and ASIC1a channels, by acidic pH and the resultant depolarization of nociceptive primary sensory neurons, participates in nociception. Agents that inhibit the activation of ASICs are thus expected to be analgesic. Here, we studied the effect of local anesthetic tetracaine on ASIC currents. RESULTS Tetracaine inhibited the peak ASIC3 current in a concentration-dependent manner with an IC50 of 9.96 ± 1.88 mM. The degree of inhibition by tetracaine was dependent on the extracellular pH but independent of the membrane potential. Furthermore, 3 mM tetracaine also inhibited 29.83% of the sustained ASIC3 current. In addition to ASIC3, tetracaine inhibited the ASIC1a and ASIC1β currents. The inhibition of the ASIC1a current was influenced by the frequency of channel activation. In contrast to ASIC3, ASIC1a, and ASIC1β currents, ASIC2a current was not inhibited by tetracaine. In cultured mouse dorsal root ganglion neurons, 1-3 mM tetracaine inhibited both the transient and sustained ASIC currents. At pH4.5, 3 mM tetracaine reduced the peak ASIC current to 60.06 ± 4.51%, and the sustained current to 48.24 ± 7.02% of the control values in dorsal root ganglion neurons. In contrast to ASICs, voltage-gated sodium channels were inhibited by acid, with 55.15% inhibition at pH6.0 and complete inhibition at pH5.0. CONCLUSIONS These findings disclose a potential new mechanism underlying the analgesic effects of local anesthetics, particularly in acidic conditions where their primary target (i.e. voltage-gated Na+ channel) has been suppressed by protons.
Collapse
|
208
|
Jing L, Chu XP, Zha XM. Three distinct motifs within the C-terminus of acid-sensing ion channel 1a regulate its surface trafficking. Neuroscience 2013; 247:321-7. [PMID: 23727453 DOI: 10.1016/j.neuroscience.2013.05.041] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2013] [Revised: 05/20/2013] [Accepted: 05/21/2013] [Indexed: 10/26/2022]
Abstract
Various protein motifs play a key role in regulating protein biogenesis and trafficking. Here, we discovered that three distinct motifs regulate the trafficking of acid-sensing ion channel 1a (ASIC1a), the primary neuronal proton receptor which plays critical roles in neurological diseases including stroke, multiple sclerosis and seizures. Mutating the PDZ binding motif of ASIC1a increased its surface expression and current density. In contrast, mutating either a RRGK motif or a KEAKR motif reduced ASIC1a surface expression and acid-activated current density. Mutating or deleting the RRGK motif also reduced pH sensitivity and the rate of desensitization of ASIC1a. These changes were likely due to a change in ASIC1a biogenesis; mutating either the RRGK or KEAKR motif reduced N-glycosylation of ASIC1a while mutating the PDZ binding motif had the opposite effect. Our results demonstrate that these C-terminal motifs are important for ASIC1a trafficking and channel function. In addition, in contrast to multiple previous studies, which all show that K/R containing motifs lead to endoplasmic reticulum (ER) retention, our findings indicate that these motifs can also be required for efficient trafficking.
Collapse
Affiliation(s)
- L Jing
- Department of Cell Biology and Neuroscience, University of South Alabama College of Medicine, 307 University Boulevard, MSB1201, Mobile, AL 36688, United States
| | | | | |
Collapse
|
209
|
|
210
|
Sinning A, Hübner CA. Minireview: pH and synaptic transmission. FEBS Lett 2013; 587:1923-8. [PMID: 23669358 DOI: 10.1016/j.febslet.2013.04.045] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 04/26/2013] [Accepted: 04/26/2013] [Indexed: 11/30/2022]
Abstract
As a general rule a rise in pH increases neuronal activity, whereas it is dampened by a fall of pH. Neuronal activity per se also challenges pH homeostasis by the increase of metabolic acid equivalents. Moreover, the negative membrane potential of neurons promotes the intracellular accumulation of protons. Synaptic key players such as glutamate receptors or voltage-gated calcium channels show strong pH dependence and effects of pH gradients on synaptic processes are well known. However, the processes and mechanisms that allow controlling the pH in synaptic structures and how these mechanisms contribute to normal synaptic function are only beginning to be resolved.
Collapse
Affiliation(s)
- Anne Sinning
- Institute of Human Genetics, University Hospital Jena, Friedrich Schiller University Jena, Kollegiengasse 10, D-07743 Jena, Germany
| | | |
Collapse
|
211
|
Jiang Q, Wang CM, Fibuch EE, Wang JQ, Chu XP. Differential regulation of locomotor activity to acute and chronic cocaine administration by acid-sensing ion channel 1a and 2 in adult mice. Neuroscience 2013; 246:170-8. [PMID: 23644053 DOI: 10.1016/j.neuroscience.2013.04.059] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Revised: 04/18/2013] [Accepted: 04/28/2013] [Indexed: 12/12/2022]
Abstract
Acid-sensing ion channels (ASICs) are densely expressed in the brain with ASIC1a and ASIC2 channels being the predominant subtypes. These channels are enriched at synaptic sites and are central for the regulation of normal synaptic transmission. Moreover, increasing evidence links ASICs to the pathogenesis of various neurological and neuropsychiatric disorders. In this study, we explore the putative role of ASIC1a and ASIC2 in the regulation of behavioral sensitivity to the psychostimulant cocaine by utilizing ASIC1a or ASIC2 knockout mice. Acute cocaine injection induced a typical dose-dependent increase in locomotor activities in wild-type (WT) mice. However, in ASIC1a and ASIC2 mutant mice, different motor responses to cocaine were observed. In ASIC1a(-/-) mice, cocaine induced a significantly less motor response at all doses (5, 10, 20, and 30 mg/kg), while in ASIC2(-/-) mice, cocaine (5-20 mg/kg) stimulated locomotor activity to an extent comparable to WT mice. Only at 30 mg/kg, the cocaine-stimulated motor activity was reduced in ASIC2(-/-) mice. In a chronic cocaine administration model (20mg/kg, once daily for 5 days), a challenge injection of cocaine (10mg/kg, after 2-week withdrawal) caused an evident behavioral sensitization in the cocaine-pretreated WT mice. This behavioral sensitization to challenge cocaine was also displayed in ASIC1a(-/-) and ASIC2(-/-) mice. However, ASIC2(-/-) mice showed less sensitization to challenge cocaine when compared to WT and ASIC1a(-/-) mice. Our results demonstrate the important role of ASIC1a and ASIC2 channels in the modulation of behavioral sensitivity to cocaine. The two synapse-enriched ASIC subtypes are believed to play distinguishable roles in the regulation of behavioral responses to acute and chronic cocaine administration.
Collapse
Affiliation(s)
- Q Jiang
- Department of Basic Medical Science, School of Medicine, University of Missouri-Kansas City, Kansas City, MO 64108, USA
| | | | | | | | | |
Collapse
|
212
|
Baron A, Diochot S, Salinas M, Deval E, Noël J, Lingueglia E. Venom toxins in the exploration of molecular, physiological and pathophysiological functions of acid-sensing ion channels. Toxicon 2013; 75:187-204. [PMID: 23624383 DOI: 10.1016/j.toxicon.2013.04.008] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Accepted: 04/10/2013] [Indexed: 02/07/2023]
Abstract
Acid-sensing ion channels (ASICs) are voltage-independent proton-gated cation channels that are largely expressed in the nervous system as well as in some non-neuronal tissues. In rodents, six different isoforms (ASIC1a, 1b, 2a, 2b, 3 and 4) can associate into homo- or hetero-trimers to form a functional channel. Specific polypeptide toxins targeting ASIC channels have been isolated from the venoms of spider (PcTx1), sea anemone (APETx2) and snakes (MitTx and mambalgins). They exhibit different and sometimes partially overlapping pharmacological profiles and are usually blockers of ASIC channels, except for MitTx, which is a potent activator. This review focuses on the use of these toxins to explore the structure-function relationships, the physiological and the pathophysiological roles of ASIC channels, illustrating at the same time the therapeutic potential of some of these natural compounds.
Collapse
Affiliation(s)
- Anne Baron
- CNRS, Institut de Pharmacologie Moléculaire et Cellulaire, UMR 7275, 06560 Valbonne, France; Université de Nice-Sophia Antipolis, 06560 Valbonne, France; LabEx Ion Channel Science and Therapeutics, 06560 Valbonne, France
| | | | | | | | | | | |
Collapse
|
213
|
Synchronization Implies Seizure or Seizure Implies Synchronization? Brain Topogr 2013; 27:112-22. [DOI: 10.1007/s10548-013-0284-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Accepted: 03/26/2013] [Indexed: 10/27/2022]
|
214
|
Zha XM. Acid-sensing ion channels: trafficking and synaptic function. Mol Brain 2013; 6:1. [PMID: 23281934 PMCID: PMC3562204 DOI: 10.1186/1756-6606-6-1] [Citation(s) in RCA: 104] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 12/20/2012] [Indexed: 01/05/2023] Open
Abstract
Extracellular acidification occurs in the brain with elevated neural activity, increased metabolism, and neuronal injury. This reduction in pH can have profound effects on brain function because pH regulates essentially every single biochemical reaction. Therefore, it is not surprising to see that Nature evolves a family of proteins, the acid-sensing ion channels (ASICs), to sense extracellular pH reduction. ASICs are proton-gated cation channels that are mainly expressed in the nervous system. In recent years, a growing body of literature has shown that acidosis, through activating ASICs, contributes to multiple diseases, including ischemia, multiple sclerosis, and seizures. In addition, ASICs play a key role in fear and anxiety related psychiatric disorders. Several recent reviews have summarized the importance and therapeutic potential of ASICs in neurological diseases, as well as the structure-function relationship of ASICs. However, there is little focused coverage on either the basic biology of ASICs or their contribution to neural plasticity. This review will center on these topics, with an emphasis on the synaptic role of ASICs and molecular mechanisms regulating the spatial distribution and function of these ion channels.
Collapse
Affiliation(s)
- Xiang-ming Zha
- Department of Cell Biology and Neuroscience, College of Medicine, University of South Alabama, 307 University Blvd, MSB1201, Mobile, AL 36688, USA.
| |
Collapse
|
215
|
Prasad PD, Datta SV, Majumdar K. Enhanced phase and amplitude synchronization toward focal seizure offset. Clin EEG Neurosci 2013; 44:16-24. [PMID: 23467797 DOI: 10.1177/1550059412456093] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Recent studies involving individual neurons in the seizure focal and surrounding areas have established heterogeneous firing patterns in single cells. However, the patterns become more homogeneous approaching the seizure offset. In this article, we show that similar observations are possible from intracranial recording if the right quantitative or engineering techniques are used. We have observed an increase in Hilbert transformation-based phase synchronization in the focal electrocorticoencehalogram (ECoG) in the gamma band (30-40 Hz) towards the end of the majority of focal epileptic seizures. An amplitude correlation measure shows an enhanced principal component (and hence enhanced correlation among the channels involved) approaching the offset of the large majority of seizures. Surprisingly, there are seizures which show the enhanced phase synchronization approaching offset but no enhanced amplitude correlation during the same period and vice versa. This study shows that suitable computational tools can sometimes compensate for more expensive and technologically demanding data acquisition systems. A possible neurophysiological explanation behind the observed phenomenon is also presented.
Collapse
|
216
|
Leng TD, Xiong ZG. The pharmacology and therapeutic potential of small molecule inhibitors of acid-sensing ion channels in stroke intervention. Acta Pharmacol Sin 2013; 34:33-8. [PMID: 22820909 DOI: 10.1038/aps.2012.81] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
In the nervous system, a decrease in extracellular pH is a common feature of various physiological and pathological processes, including synaptic transmission, cerebral ischemia, epilepsy, brain trauma, and tissue inflammation. Acid-sensing ion channels (ASICs) are proton-gated cation channels that are distributed throughout the central and peripheral nervous systems. Following the recent identification of ASICs as critical acid-sensing extracellular proton receptors, growing evidence has suggested that the activation of ASICs plays important roles in physiological processes such as nociception, mechanosensation, synaptic plasticity, learning and memory. However, the over-activation of ASICs is also linked to adverse outcomes for certain pathological processes, such as brain ischemia and multiple sclerosis. Based on the well-demonstrated role of ASIC1a activation in acidosis-mediated brain injury, small molecule inhibitors of ASIC1a may represent novel therapeutic agents for the treatment of neurological disorders, such as stroke.
Collapse
|
217
|
Human seizures self-terminate across spatial scales via a critical transition. Proc Natl Acad Sci U S A 2012; 109:21116-21. [PMID: 23213262 DOI: 10.1073/pnas.1210047110] [Citation(s) in RCA: 133] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Why seizures spontaneously terminate remains an unanswered fundamental question of epileptology. Here we present evidence that seizures self-terminate via a discontinuous critical transition or bifurcation. We show that human brain electrical activity at various spatial scales exhibits common dynamical signatures of an impending critical transition--slowing, increased correlation, and flickering--in the approach to seizure termination. In contrast, prolonged seizures (status epilepticus) repeatedly approach, but do not cross, the critical transition. To support these results, we implement a computational model that demonstrates that alternative stable attractors, representing the ictal and postictal states, emulate the observed dynamics. These results suggest that self-terminating seizures end through a common dynamical mechanism. This description constrains the specific biophysical mechanisms underlying seizure termination, suggests a dynamical understanding of status epilepticus, and demonstrates an accessible system for studying critical transitions in nature.
Collapse
|
218
|
Helmy MM, Ruusuvuori E, Watkins PV, Voipio J, Kanold PO, Kaila K. Acid extrusion via blood-brain barrier causes brain alkalosis and seizures after neonatal asphyxia. ACTA ACUST UNITED AC 2012; 135:3311-9. [PMID: 23125183 PMCID: PMC3501974 DOI: 10.1093/brain/aws257] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Birth asphyxia is often associated with a high seizure burden that is predictive of poor neurodevelopmental outcome. The mechanisms underlying birth asphyxia seizures are unknown. Using an animal model of birth asphyxia based on 6-day-old rat pups, we have recently shown that the seizure burden is linked to an increase in brain extracellular pH that consists of the recovery from the asphyxia-induced acidosis, and of a subsequent plateau level well above normal extracellular pH. In the present study, two-photon imaging of intracellular pH in neocortical neurons in vivo showed that pH changes also underwent a biphasic acid–alkaline response, resulting in an alkaline plateau level. The mean alkaline overshoot was strongly suppressed by a graded restoration of normocapnia after asphyxia. The parallel post-asphyxia increase in extra- and intracellular pH levels indicated a net loss of acid equivalents from brain tissue that was not attributable to a disruption of the blood–brain barrier, as demonstrated by a lack of increased sodium fluorescein extravasation into the brain, and by the electrophysiological characteristics of the blood–brain barrier. Indeed, electrode recordings of pH in the brain and trunk demonstrated a net efflux of acid equivalents from the brain across the blood–brain barrier, which was abolished by the Na/H exchange inhibitor, N-methyl-isobutyl amiloride. Pharmacological inhibition of Na/H exchange also suppressed the seizure activity associated with the brain-specific alkalosis. Our findings show that the post-asphyxia seizures are attributable to an enhanced Na/H exchange-dependent net extrusion of acid equivalents across the blood–brain barrier and to consequent brain alkalosis. These results suggest targeting of blood–brain barrier-mediated pH regulation as a novel approach in the prevention and therapy of neonatal seizures.
Collapse
Affiliation(s)
- Mohamed M Helmy
- Department of Biosciences, University of Helsinki, Helsinki, Finland
| | | | | | | | | | | |
Collapse
|
219
|
Holland PR, Akerman S, Andreou AP, Karsan N, Wemmie JA, Goadsby PJ. Acid-sensing ion channel 1: A novel therapeutic target for migraine with aura. Ann Neurol 2012; 72:559-63. [DOI: 10.1002/ana.23653] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
220
|
Chu XP, Xiong ZG. Physiological and pathological functions of acid-sensing ion channels in the central nervous system. Curr Drug Targets 2012; 13:263-71. [PMID: 22204324 DOI: 10.2174/138945012799201685] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Revised: 08/08/2011] [Accepted: 08/12/2011] [Indexed: 12/20/2022]
Abstract
Protons are important signals for neuronal function. In the central nervous system (CNS), proton concentrations change locally when synaptic vesicles release their acidic contents into the synaptic cleft, and globally in ischemia, seizures, traumatic brain injury, and other neurological disorders due to lactic acid accumulation. The finding that protons gate a distinct family of ion channels, the acid-sensing ion channels (ASICs), has shed new light on the mechanism of acid signaling and acidosis-associated neuronal injury. Accumulating evidence has suggested that ASICs play important roles in physiological processes such as synaptic plasticity, learning/memory, fear conditioning, and retinal integrity, and in pathological conditions such as brain ischemia, multiple sclerosis, epileptic seizures, and malignant glioma. Thus, targeting these channels may lead to novel therapeutic interventions for neurological disorders. The goal of this review is to provide an update on recent advances in our understanding of the functions of ASICs in the CNS.
Collapse
Affiliation(s)
- Xiang-Ping Chu
- Department of Basic Medical Science, School of Medicine, University of Missouri-Kansas City, Kansas City, MO 64108, USA.
| | | |
Collapse
|
221
|
Lu Y, Yi L, Liu D, Li J, Sun L, Zhang Z. Alkalosis leads to the over-activity of cortical principal neurons. Neurosci Lett 2012; 525:117-22. [DOI: 10.1016/j.neulet.2012.07.034] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2012] [Revised: 06/08/2012] [Accepted: 07/19/2012] [Indexed: 10/28/2022]
|
222
|
Petroff E, Snitsarev V, Gong H, Abboud FM. Acid sensing ion channels regulate neuronal excitability by inhibiting BK potassium channels. Biochem Biophys Res Commun 2012; 426:511-5. [PMID: 22960074 DOI: 10.1016/j.bbrc.2012.08.114] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2012] [Accepted: 08/22/2012] [Indexed: 11/25/2022]
Abstract
Acid sensing ion channels (ASICs), Ca(2+) and voltage-activated potassium channels (BK) are widely present throughout the central nervous system. Previous studies have shown that when expressed together in heterologous cells, ASICs inhibit BK channels, and this inhibition is relieved by acidic extracellular pH. We hypothesized that ASIC and BK channels might interact in neurons, and that ASICs may regulate BK channel activity. We found that ASICs inhibited BK currents in cultured wild-type cortical neurons, but not in ASIC1a/2/3 triple knockout neurons. The inhibition in the wild-type was partially relieved by a drop in extracellular pH to 6. To test the consequences of ASIC-BK interaction for neuronal excitability, we compared action potential firing in cultured cortical neurons from wild-type and ASIC1a/2/3 null mice. We found that in the knockout, action potentials were narrow and exhibited increased after-hyperpolarization. Moreover, the excitability of these neurons was significantly increased. These findings are consistent with increased BK channel activity in the neurons from ASIC1a/2/3 null mice. Our data suggest that ASICs can act as endogenous pH-dependent inhibitors of BK channels, and thereby can reduce neuronal excitability.
Collapse
Affiliation(s)
- Elena Petroff
- Department of Biology and Molecular Biology, Montclair State University, Montclair, NJ 07043, USA.
| | | | | | | |
Collapse
|
223
|
BAD-dependent regulation of fuel metabolism and K(ATP) channel activity confers resistance to epileptic seizures. Neuron 2012; 74:719-30. [PMID: 22632729 DOI: 10.1016/j.neuron.2012.03.032] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/08/2012] [Indexed: 01/07/2023]
Abstract
Neuronal excitation can be substantially modulated by alterations in metabolism, as evident from the anticonvulsant effect of diets that reduce glucose utilization and promote ketone body metabolism. We provide genetic evidence that BAD, a protein with dual functions in apoptosis and glucose metabolism, imparts reciprocal effects on metabolism of glucose and ketone bodies in brain cells. These effects involve phosphoregulation of BAD and are independent of its apoptotic function. BAD modifications that reduce glucose metabolism produce a marked increase in the activity of metabolically sensitive K(ATP) channels in neurons, as well as resistance to behavioral and electrographic seizures in vivo. Seizure resistance is reversed by genetic ablation of the K(ATP) channel, implicating the BAD-K(ATP) axis in metabolic control of neuronal excitation and seizure responses.
Collapse
|
224
|
Sherwood TW, Frey EN, Askwith CC. Structure and activity of the acid-sensing ion channels. Am J Physiol Cell Physiol 2012; 303:C699-710. [PMID: 22843794 DOI: 10.1152/ajpcell.00188.2012] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The acid-sensing ion channels (ASICs) are a family of proton-sensing channels expressed throughout the nervous system. Their activity is linked to a variety of complex behaviors including fear, anxiety, pain, depression, learning, and memory. ASICs have also been implicated in neuronal degeneration accompanying ischemia and multiple sclerosis. As a whole, ASICs represent novel therapeutic targets for several clinically important disorders. An understanding of the correlation between ASIC structure and function will help to elucidate their mechanism of action and identify potential therapeutics that specifically target these ion channels. Despite the seemingly simple nature of proton binding, multiple studies have shown that proton-dependent gating of ASICs is quite complex, leading to activation and desensitization through distinct structural components. This review will focus on the structural aspects of ASIC gating in response to both protons and the newly discovered activators GMQ and MitTx. ASIC modulatory compounds and their action on proton-dependent gating will also be discussed. This review is dedicated to the memory of Dale Benos, who made a substantial contribution to our understanding of ASIC activity.
Collapse
Affiliation(s)
- Thomas W Sherwood
- Dept. of Neuroscience, The Ohio State Univ. Wexner Medical Center, Columbus, OH 43210, USA
| | | | | |
Collapse
|
225
|
Jiang Q, Zha XM, Chu XP. Inhibition of human acid-sensing ion channel 1b by zinc. INTERNATIONAL JOURNAL OF PHYSIOLOGY, PATHOPHYSIOLOGY AND PHARMACOLOGY 2012; 4:84-93. [PMID: 22837807 PMCID: PMC3403561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 04/04/2012] [Accepted: 05/08/2012] [Indexed: 06/01/2023]
Abstract
Acid-sensing ion channel 1b (ASIC1b) is expressed in peripheral sensory neurons and has been implicated in nociception. Understanding the modulation of ASIC1b will provide important insight into how ASIC1b contributes to pain sensation. In our previous study, we showed that zinc, an important modulator of pain sensation, reduces rat ASIC1b current. However, rat ASIC1b shows several important differences from its recently identified human homolog. Most noticeably, human ASIC1b (hASIC1b) has a sustained component, which may play a role in persistent pain. Therefore, we tested here the hypothesis that zinc modulates the current properties of hASIC1b. Bath application of zinc suppressed the peak amplitude of hASIC1b currents, with a half-maximum inhibitory concentration of 37 μM. However, zinc did not affect the sustained component of hASIC1b currents. The effect of zinc was independent of pH-dependent activation, steady-state desensitization, and extracellular Ca(2+), suggesting noncompetitive mechanisms. Further, we found that extracellular site(s) of the hASIC1b subunit is important for the effect of zinc. Mutating cysteine 196, but not cysteine 309, in the extracellular domain of the hASIC1b abolished the zinc inhibition. These results suggest that, through modulating cysteine196, zinc may have a modulatory role in acute pain.
Collapse
Affiliation(s)
- Qian Jiang
- Department of Basic Medical Science, University of Missouri-Kansas City School of MedicineKansas City, MO 64108, USA
| | - Xiang-Ming Zha
- Department of Cell Biology and Neuroscience, University of South Alabama College of MedicineMobile, AL 36688, USA
| | - Xiang-Ping Chu
- Department of Basic Medical Science, University of Missouri-Kansas City School of MedicineKansas City, MO 64108, USA
| |
Collapse
|
226
|
N-glycosylation of acid-sensing ion channel 1a regulates its trafficking and acidosis-induced spine remodeling. J Neurosci 2012; 32:4080-91. [PMID: 22442073 DOI: 10.1523/jneurosci.5021-11.2012] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Acid-sensing ion channel-1a (ASIC1a) is a potential therapeutic target for multiple neurological diseases. We studied here ASIC1a glycosylation and trafficking, two poorly understood processes pivotal in determining the functional outcome of an ion channel. We found that most ASIC1a in the mouse brain was fully glycosylated. Inhibiting glycosylation with tunicamycin reduced ASIC1a surface trafficking, dendritic targeting, and acid-activated current density. N-glycosylation of the two glycosylation sites, Asn393 and Asn366, has differential effects on ASIC1a biogenesis. Maturation of Asn393 increased ASIC1a surface and dendritic trafficking, pH sensitivity, and current density. In contrast, glycosylation of Asn366 was dispensable for ASIC1a function and may be a rate-limiting step in ASIC1a biogenesis. In addition, we revealed that acidosis reduced the density and length of dendritic spines in a time- and ASIC1a-dependent manner. ASIC1a N366Q, which showed increased glycosylation and dendritic targeting, potentiated acidosis-induced spine loss. Conversely, ASIC1a N393Q, which had diminished dendritic targeting and inhibited ASIC1a current dominant-negatively, had the opposite effect. These data tie N-glycosylation of ASIC1a with its trafficking. More importantly, by revealing a site-specific effect of acidosis on dendritic spines, our findings suggest that these processes have an important role in regulating synaptic plasticity and determining long-term consequences in diseases that generate acidosis.
Collapse
|
227
|
Xiong QJ, Hu ZL, Wu PF, Ni L, Deng ZF, Wu WN, Chen JG, Wang F. Acid-sensing ion channels contribute to the increase in vesicular release from SH-SY5Y cells stimulated by extracellular protons. Am J Physiol Cell Physiol 2012; 303:C376-84. [PMID: 22592406 DOI: 10.1152/ajpcell.00067.2012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Acid-sensing ion channels (ASICs) have been reported to play a role in the neuronal dopamine pathway, but the exact role in neurotransmitter release remains elusive. Human neuroblastoma SH-SY5Y is a dopaminergic neuronal cell line, which can release monoamine neurotransmitters. In this study, the expression of ASICs was identified in SH-SY5Y cells to further explore the role of ASICs in vesicular release stimulated by acid. We gathered evidence that ASICs could be detected in SH-SY5Y cells. In whole cell patch-clamp recording, a rapid decrease in extracellular pH evoked inward currents, which were reversibly inhibited by 100 μM amiloride. The currents were pH dependent, with a pH of half-maximal activation (pH(0.5)) of 6.01 ± 0.04. Furthermore, in calcium imaging and FM 1-43 dye labeling, it was shown that extracellular protons increased intracellular calcium levels and vesicular release in SH-SY5Y cells, which was attenuated by PcTx1 and amiloride. Interestingly, N-type calcium channel blockers inhibited the vesicular release induced by acidification. In conclusion, ASICs are functionally expressed in SH-SY5Y cells and involved in vesicular release stimulated by acidification. N-type calcium channels may be involved in the increase in vesicular release induced by acid. Our results provide a preliminary study on ASICs in SH-SY5Y cells and neurotransmitter release, which helps to further investigate the relationship between ASICs and dopaminergic neurons.
Collapse
Affiliation(s)
- Qiu-Ju Xiong
- Department of Pharmacology, School of Basic Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | | | | | | | | | | | | | | |
Collapse
|
228
|
Abstract
Localized pH changes have been suggested to occur in the brain during normal function. However, the existence of such pH changes has also been questioned. Lack of methods for noninvasively measuring pH with high spatial and temporal resolution has limited insight into this issue. Here we report that a magnetic resonance imaging (MRI) strategy, T(1) relaxation in the rotating frame (T(1)ρ), is sufficiently sensitive to detect widespread pH changes in the mouse and human brain evoked by systemically manipulating carbon dioxide or bicarbonate. Moreover, T(1)ρ detected a localized acidosis in the human visual cortex induced by a flashing checkerboard. Lactate measurements and pH-sensitive (31)P spectroscopy at the same site also identified a localized acidosis. Consistent with the established role for pH in blood flow recruitment, T(1)ρ correlated with blood oxygenation level-dependent contrast commonly used in functional MRI. However, T(1)ρ was not directly sensitive to blood oxygen content. These observations indicate that localized pH fluctuations occur in the human brain during normal function. Furthermore, they suggest a unique functional imaging strategy based on pH that is independent of traditional functional MRI contrast mechanisms.
Collapse
|
229
|
Zeng WZ, Xu TL. Proton production, regulation and pathophysiological roles in the mammalian brain. Neurosci Bull 2012; 28:1-13. [PMID: 22233885 DOI: 10.1007/s12264-012-1068-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The recent demonstration of proton signaling in C. elegans muscle contraction suggests a novel mechanism for proton-based intercellular communication and has stimulated enthusiasm for exploring proton signaling in higher organisms. Emerging evidence indicates that protons are produced and regulated in localized space and time. Furthermore, identification of proton regulators and sensors in the brain leads to the speculation that proton production and regulation may be of major importance for both physiological and pathological functions ranging from nociception to learning and memory. Extracellular protons may play a role in signal transmission by not only acting on adjacent cells but also affecting the cell from which they were released. In this review, we summarize the upstream and downstream pathways of proton production and regulation in the mammalian brain, with special emphasis on the proton extruders and sensors that are critical in the homeostatic regulation of pH, and discuss their potential roles in proton signaling under normal and pathophysiological conditions.
Collapse
Affiliation(s)
- Wei-Zheng Zeng
- Neuroscience Division, Department of Biochemistry and Molecular Cell Biology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | | |
Collapse
|
230
|
Yang Y, Yu Y, Cheng J, Liu Y, Liu DS, Wang J, Zhu MX, Wang R, Xu TL. Highly conserved salt bridge stabilizes rigid signal patch at extracellular loop critical for surface expression of acid-sensing ion channels. J Biol Chem 2012; 287:14443-55. [PMID: 22399291 DOI: 10.1074/jbc.m111.334250] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Acid-sensing ion channels (ASICs) are non-selective cation channels activated by extracellular acidosis associated with many physiological and pathological conditions. A detailed understanding of the mechanisms that govern cell surface expression of ASICs, therefore, is critical for better understanding of the cell signaling under acidosis conditions. In this study, we examined the role of a highly conserved salt bridge residing at the extracellular loop of rat ASIC3 (Asp(107)-Arg(153)) and human ASIC1a (Asp(107)-Arg(160)) channels. Comprehensive mutagenesis and electrophysiological recordings revealed that the salt bridge is essential for functional expression of ASICs in a pH sensing-independent manner. Surface biotinylation and immunolabeling of an extracellular epitope indicated that mutations, including even minor alterations, at the salt bridge impaired cell surface expression of ASICs. Molecular dynamics simulations, normal mode analysis, and further mutagenesis studies suggested a high stability and structural constrain of the salt bridge, which serves to separate an adjacent structurally rigid signal patch, important for surface expression, from a flexible gating domain. Thus, we provide the first evidence of structural requirement that involves a stabilizing salt bridge and an exposed rigid signal patch at the destined extracellular loop for normal surface expression of ASICs. These findings will allow evaluation of new strategies aimed at preventing excessive excitability and neuronal injury associated with tissue acidosis and ASIC activation.
Collapse
Affiliation(s)
- Yang Yang
- Key Laboratory of Preclinical Study for New Drugs of Gansu Province, School of Basic Medical Sciences, Lanzhou University, Lanzhou 730000, China
| | | | | | | | | | | | | | | | | |
Collapse
|
231
|
Sun L, Zhang K, Li J, Liu D, Lu Y, Zhang Z. An impairment of cortical GABAergic neurons is involved in alkalosis-induced brain dysfunctions. Biochem Biophys Res Commun 2012; 419:627-31. [PMID: 22369942 DOI: 10.1016/j.bbrc.2012.02.061] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Accepted: 02/09/2012] [Indexed: 10/28/2022]
Abstract
Acid-base imbalance leads to pathological cognition and behaviors in the clinical practices. In the comparison with acidosis, the cellular mechanisms underlying alkalosis-induced brain dysfunction remain unclear. By using electrophysiological approach, we investigated the influences of high extracellular pH environment on cortical GABAergic neurons in terms of their responsiveness to synaptic inputs and their ability to produce action potentials. Artificial cerebral spinal fluid in high pH impairs excitatory synaptic transmission and spike initiation in cortical GABAergic neurons. The alkalosis-induced dysfunction of GABAergic neurons is associated with the decrease of receptor responsiveness and the increases of spike refractory periods and threshold potentials. Our studies reveal that alkalosis impairs cortical GABAergic neurons and subsequently deteriorate brain functions. The molecular targets for alkalosis action include glutamate receptor-channels and voltage-gated sodium channels on GABAergic neurons.
Collapse
Affiliation(s)
- Ling Sun
- Department of Neurology, The First Affiliated Hospital, Harbin Medical University, Harbin, Heilongjiang 150001, PR China
| | | | | | | | | | | |
Collapse
|
232
|
Chen CR, Tan R, Qu WM, Wu Z, Wang Y, Urade Y, Huang ZL. Magnolol, a major bioactive constituent of the bark of Magnolia officinalis, exerts antiepileptic effects via the GABA/benzodiazepine receptor complex in mice. Br J Pharmacol 2012; 164:1534-46. [PMID: 21518336 DOI: 10.1111/j.1476-5381.2011.01456.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE The aim of this study was to evaluate the anti-convulsant effects of magnolol (6, 6', 7, 12-tetramethoxy-2, 2'-dimethyl-1-β-berbaman, C18H18O2) and the mechanisms involved. EXPERIMENTAL APPROACH Mice were treated with magnolol (20, 40 and 80 mg·kg(-1)) 30 min before injection with pentylenetetrazol (PTZ, 60 mg·kg(-1), i.p.). The anti-seizure effects of magnolol were analysed using seizure models of behaviour, EEG and in vitro electrophysiology and c-Fos expression in the hippocampus and cortex. KEY RESULTS Magnolol at doses of 40 and 80 mg·kg(-1) significantly delayed the onset of myoclonic jerks and generalized clonic seizures, and decreased the seizure stage and mortality compared with those of the vehicle-treated animals. EEG recordings showed that magnolol (40 and 80 mg·kg(-1)) prolonged the latency of seizure onset and decreased the number of seizure spikes. The anti-epileptic effect of magnolol was reversed by the GABA(A)/benzodiazepine receptor antagonist flumazenil. Pretreatment with flumazenil decreased the effects of magnolol on prolongation of seizure latency and decline of seizure stage. In a Mg(2+)-free model of epileptiform activity, using multi-electrode array recordings in mouse hippocampal slices, magnolol decreased spontaneous epileptiform discharges. Magnolol also significantly decreased seizure-induced Fos immunoreactivity in the piriform cortex, dentate gyrus and hippocampal area CA1. These effects were attenuated by pretreatment with flumazenil. CONCLUSIONS AND IMPLICATIONS These findings indicate that the inhibitory effects of magnolol on epileptiform activity were mediated by the GABA(A) /benzodiazepine receptor complex.
Collapse
Affiliation(s)
- C R Chen
- Department of Pharmacology, Shanghai Medical College, Fudan University, Shanghai, China
| | | | | | | | | | | | | |
Collapse
|
233
|
Abstract
The epithelial Na(+) channel (ENaC) and acid-sensitive ion channel (ASIC) branches of the ENaC/degenerin superfamily of cation channels have drawn increasing attention as potential therapeutic targets in a variety of diseases and conditions. Originally thought to be solely expressed in fluid absorptive epithelia and in neurons, it has become apparent that members of this family exhibit nearly ubiquitous expression. Therapeutic opportunities range from hypertension, due to the role of ENaC in maintaining whole body salt and water homeostasis, to anxiety disorders and pain associated with ASIC activity. As a physiologist intrigued by the fundamental mechanics of salt and water transport, it was natural that Dale Benos, to whom this series of reviews is dedicated, should have been at the forefront of research into the amiloride-sensitive sodium channel. The cloning of ENaC and subsequently the ASIC channels has revealed a far wider role for this channel family than was previously imagined. In this review, we will discuss the known and potential roles of ENaC and ASIC subunits in the wide variety of pathologies in which these channels have been implicated. Some of these, such as the role of ENaC in Liddle's syndrome are well established, others less so; however, all are related in that the fundamental defect is due to inappropriate channel activity.
Collapse
Affiliation(s)
- Yawar J Qadri
- Department of Physiology and Biophysics, University of Alabama at Birmingham, AL 35294, USA
| | | | | |
Collapse
|
234
|
Wlaź P, Socała K, Nieoczym D, Łuszczki JJ, Zarnowska I, Zarnowski T, Czuczwar SJ, Gasior M. Anticonvulsant profile of caprylic acid, a main constituent of the medium-chain triglyceride (MCT) ketogenic diet, in mice. Neuropharmacology 2011; 62:1882-9. [PMID: 22210332 DOI: 10.1016/j.neuropharm.2011.12.015] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2011] [Revised: 12/02/2011] [Accepted: 12/10/2011] [Indexed: 12/14/2022]
Abstract
The purpose of the present study was to evaluate the acute anticonvulsant effects of caprylic acid (CA), the main constituent of the medium-chain triglyceride ketogenic diet (MCT KD), in seizure tests typically used in screening for potential antiepileptic drugs in mice. Pharmacodynamic and pharmacokinetic interactions between CA and valproate (VPA) were also investigated. CA (p.o.) and VPA (i.p.) were administered 30 min before testing. Acute effects on motor coordination were assessed in the chimney test. Total plasma and brain concentrations of CA and VPA, when administered alone or in combination, were determined by high performance liquid chromatography. CA (10-30 mmol/kg) increased the threshold for i.v. pentylenetetrazole-induced myoclonic and clonic convulsions, but not tonic convulsions. CA (5-30 mmol/kg) increased the threshold for 6-Hz psychomotor seizures but was ineffective in the maximal electroshock seizure threshold test. CA (10-60 mmol/kg p.o.) impaired motor performance in the chimney test (TD(50) value, 58.4 mmol/kg). Increasing doses of CA (5-30 mmol/kg) produced proportional increases in plasma and brain exposure with constant brain/plasma partitioning. CA increased anticonvulsant potency of VPA in the maximal electroshock seizure and 6-Hz seizure tests. Co-administration of CA and VPA had no effect on brain and plasma concentrations of either compound. In summary, CA exerts acute anticonvulsant effects and potentiates the anticonvulsant effect of VPA at doses that result in plasma exposures comparable to those reported in epileptic patients on the MCT KD. Thus, this acute anticonvulsant property of CA may benefit and add to the overall clinical efficacy of the MCT KD.
Collapse
Affiliation(s)
- Piotr Wlaź
- Department of Animal Physiology, Institute of Biology and Biochemistry, Maria Curie-Skłodowska University, Lublin, Poland
| | | | | | | | | | | | | | | |
Collapse
|
235
|
Albertazzi L, Brondi M, Pavan GM, Sato SS, Signore G, Storti B, Ratto GM, Beltram F. Dendrimer-based fluorescent indicators: in vitro and in vivo applications. PLoS One 2011; 6:e28450. [PMID: 22163303 PMCID: PMC3233578 DOI: 10.1371/journal.pone.0028450] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 11/08/2011] [Indexed: 01/31/2023] Open
Abstract
Background The development of fluorescent proteins and synthetic molecules whose fluorescence properties are controlled by the environment makes it possible to monitor physiological and pathological events in living systems with minimal perturbation. A large number of small organic dyes are available and routinely used to measure biologically relevant parameters. Unfortunately their application is hindered by a number of limitations stemming from the use of these small molecules in the biological environment. Principal Findings We present a novel dendrimer-based architecture leading to multifunctional sensing elements that can overcome many of these problems. Applications in vitro, in living cells and in vivo are reported. In particular, we image for the first time extracellular pH in the brain in a mouse epilepsy model. Conclusion We believe that the proposed architecture can represent a useful and novel tool in fluorescence imaging that can be widely applied in conjunction with a broad range of sensing dyes and experimental setups.
Collapse
Affiliation(s)
- Lorenzo Albertazzi
- Laboratorio NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Pisa, Italy.
| | | | | | | | | | | | | | | |
Collapse
|
236
|
|
237
|
Jing L, Jiang YQ, Jiang Q, Wang B, Chu XP, Zha XM. The interaction between the first transmembrane domain and the thumb of ASIC1a is critical for its N-glycosylation and trafficking. PLoS One 2011; 6:e26909. [PMID: 22046405 PMCID: PMC3203923 DOI: 10.1371/journal.pone.0026909] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Accepted: 10/06/2011] [Indexed: 12/25/2022] Open
Abstract
Acid-sensing ion channel-1a (ASIC1a), the primary proton receptor in the brain, contributes to multiple diseases including stroke, epilepsy and multiple sclerosis. Thus, a better understanding of its biogenesis will provide important insights into the regulation of ASIC1a in diseases. Interestingly, ASIC1a contains a large, yet well organized ectodomain, which suggests the hypothesis that correct formation of domain-domain interactions at the extracellular side is a key regulatory step for ASIC1a maturation and trafficking. We tested this hypothesis here by focusing on the interaction between the first transmembrane domain (TM1) and the thumb of ASIC1a, an interaction known to be critical in channel gating. We mutated Tyr71 and Trp287, two key residues involved in the TM1-thumb interaction in mouse ASIC1a, and found that both Y71G and W287G decreased synaptic targeting and surface expression of ASIC1a. These defects were likely due to altered folding; both mutants showed increased resistance to tryptic cleavage, suggesting a change in conformation. Moreover, both mutants lacked the maturation of N-linked glycans through mid to late Golgi. These data suggest that disrupting the interaction between TM1 and thumb alters ASIC1a folding, impedes its glycosylation and reduces its trafficking. Moreover, reducing the culture temperature, an approach commonly used to facilitate protein folding, increased ASIC1a glycosylation, surface expression, current density and slowed the rate of desensitization. These results suggest that correct folding of extracellular ectodomain plays a critical role in ASIC1a biogenesis and function.
Collapse
Affiliation(s)
- Lan Jing
- Department of Cell Biology and Neuroscience, University of South Alabama College of Medicine, Mobile, Alabama, United States of America
- State Key Lab of New Drug & Pharmaceutical Process, Shanghai Institute of Pharmaceutical Industry, Shanghai, China
| | - Yu-Qing Jiang
- Department of Cell Biology and Neuroscience, University of South Alabama College of Medicine, Mobile, Alabama, United States of America
- Department of Urology, The Third Hospital of Hebei Medical University, ShiJiaZhuang, HeBei Province, China
| | - Qian Jiang
- Departments of Basic Medical Sciences and Anesthesiology, University of Missouri- Kansas City School of Medicine, Kansas City, Missouri, United States of America
| | - Bin Wang
- Department of Mathematics and Statistics, University of South Alabama, Mobile, Alabama, United States of America
| | - Xiang-Ping Chu
- Departments of Basic Medical Sciences and Anesthesiology, University of Missouri- Kansas City School of Medicine, Kansas City, Missouri, United States of America
| | - Xiang-ming Zha
- Department of Cell Biology and Neuroscience, University of South Alabama College of Medicine, Mobile, Alabama, United States of America
- * E-mail:
| |
Collapse
|
238
|
Li WG, Yu Y, Huang C, Cao H, Xu TL. Nonproton ligand sensing domain is required for paradoxical stimulation of acid-sensing ion channel 3 (ASIC3) channels by amiloride. J Biol Chem 2011; 286:42635-42646. [PMID: 21998313 DOI: 10.1074/jbc.m111.289058] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Acid-sensing ion channels (ASICs), which belong to the epithelial sodium channel/degenerin family, are activated by extracellular protons and are inhibited by amiloride (AMI), an important pharmacological tool for studying all known members of epithelial sodium channel/degenerin. In this study, we reported that AMI paradoxically opened homomeric ASIC3 and heteromeric ASIC3 plus ASIC1b channels at neutral pH and synergistically enhanced channel activation induced by mild acidosis (pH 7.2 to 6.8). The characteristic profile of AMI stimulation of ASIC3 channels was reminiscent of the channel activation by the newly identified nonproton ligand, 2-guanidine-4-methylquinazoline. Using site-directed mutagenesis, we showed that ASIC3 activation by AMI, but not its inhibitory effect, was dependent on the integrity of the nonproton ligand sensing domain in ASIC3 channels. Moreover, the structure-activity relationship study demonstrated the differential requirement of the 5-amino group in AMI for the stimulation or inhibition effect, strengthening the different interactions within ASIC3 channels that confer the paradoxical actions of AMI. Furthermore, using covalent modification analyses, we provided strong evidence supporting the nonproton ligand sensing domain is required for the stimulation of ASIC3 channels by AMI. Finally, we showed that AMI causes pain-related behaviors in an ASIC3-dependent manner. These data reinforce the idea that ASICs can sense nonproton ligands in addition to protons. The results also indicate caution in the use of AMI for studying ASIC physiology and in the development of AMI-derived ASIC inhibitors for treating pain syndromes.
Collapse
Affiliation(s)
- Wei-Guang Li
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031; Departments of Biochemistry and Molecular Cell Biology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Ye Yu
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031; Department of Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Chen Huang
- Departments of Biochemistry and Molecular Cell Biology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Hui Cao
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031; Departments of Biochemistry and Molecular Cell Biology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China
| | - Tian-Le Xu
- Institute of Neuroscience and State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031; Departments of Biochemistry and Molecular Cell Biology, Institute of Medical Sciences, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, China.
| |
Collapse
|
239
|
Acidosis, acid-sensing ion channels, and neuronal cell death. Mol Neurobiol 2011; 44:350-8. [PMID: 21932071 DOI: 10.1007/s12035-011-8204-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 09/01/2011] [Indexed: 10/17/2022]
Abstract
Acidosis is a common feature of many neuronal diseases and often accompanied with adverse consequences such as pain and neuronal injury. Before the discovery of acid-sensing ion channels (ASICs), protons were usually considered as a modulator of other ion channels, such as voltage-gated calcium channels, N-methyl-D-aspartate, and γ-amino butyric acid(A) receptor channels. Accordingly, the functional effects of acidosis were considered as consequences of modulations of these channels. Since the first cloning of ASICs in 1997, the conventional view on acidosis-mediated pain and cell injury has been dramatically changed. To date, ASICs, which are directly activated by extracellular protons, are shown to mediate most of the acidosis-associated physiological and pathological functions. For example, ASIC1a channels are reported to mediate acidosis-induced ischemic neuronal death. In this article, we will review the possible mechanisms that underlie ASIC1a channel-mediated neuronal death and discuss ASIC1a channel modulators involved in this process.
Collapse
|
240
|
Heteromeric acid-sensing ion channels (ASICs) composed of ASIC2b and ASIC1a display novel channel properties and contribute to acidosis-induced neuronal death. J Neurosci 2011; 31:9723-34. [PMID: 21715637 DOI: 10.1523/jneurosci.1665-11.2011] [Citation(s) in RCA: 175] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Acid-sensing ion channel (ASIC) subunits associate to form homomeric or heteromeric proton-gated ion channels in neurons throughout the nervous system. The ASIC1a subunit plays an important role in establishing the kinetics of proton-gated currents in the CNS, and activation of ASIC1a homomeric channels induces neuronal death after local acidosis that accompanies cerebral ischemia. The ASIC2b subunit is expressed in the brain in a pattern that overlaps ASIC1a, yet the contribution of ASIC2b has remained elusive. We find that coexpression of ASIC2b with ASIC1a in Xenopus oocytes results in novel proton-gated currents with properties distinct from ASIC1a homomeric channels. In particular, ASIC2b/1a heteromeric channels are inhibited by the nonselective potassium channel blockers tetraethylammonium and barium. In addition, steady-state desensitization is induced at more basic pH values, and Big Dynorphin sensitivity is enhanced in these unique heteromeric channels. Cultured hippocampal neurons show proton-gated currents consistent with ASIC2b contribution, and these currents are lacking in neurons from mice with an ACCN1 (ASIC2) gene disruption. Finally, we find that these ASIC2b/1a heteromeric channels contribute to acidosis-induced neuronal death. Together, our results show that ASIC2b confers unique properties to heteromeric channels in central neurons. Furthermore, these data indicate that ASIC2, like ASIC1, plays a role in acidosis-induced neuronal death and implicate the ASIC2b/1a subtype as a novel pharmacological target to prevent neuronal injury after stroke.
Collapse
|
241
|
Schuchmann S, Hauck S, Henning S, Grüters-Kieslich A, Vanhatalo S, Schmitz D, Kaila K. Respiratory alkalosis in children with febrile seizures. Epilepsia 2011; 52:1949-55. [DOI: 10.1111/j.1528-1167.2011.03259.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
|
242
|
Moseley BD, Ghearing GR, Benarroch EE, Britton JW. Early seizure termination in ictal asystole. Epilepsy Res 2011; 97:220-4. [PMID: 21899987 DOI: 10.1016/j.eplepsyres.2011.08.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2011] [Revised: 08/12/2011] [Accepted: 08/14/2011] [Indexed: 12/26/2022]
Abstract
To evaluate the association between cerebral hypoperfusion and seizure termination, we compared seizure duration in seven patients with syncopal ictal asystole (IA), seven with non-syncopal ictal bradycardia, and ten with non-bradycardic seizures. Mean seizure duration was 34.4±13 s in IA, 67±28.9 s in ictal bradycardia, and 82.1±31.1 in non-bradycardic seizures. These were significantly different (ANOVA, p<0.02). This suggests cerebral hypoxia-ischemia favors seizure termination.
Collapse
|
243
|
Vincent RD, Courville A, Pineau J. A bistable computational model of recurring epileptiform activity as observed in rodent slice preparations. Neural Netw 2011; 24:526-37. [DOI: 10.1016/j.neunet.2011.03.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2010] [Revised: 02/01/2011] [Accepted: 03/01/2011] [Indexed: 11/17/2022]
|
244
|
Chen X, Whissell P, Orser BA, MacDonald JF. Functional modifications of acid-sensing ion channels by ligand-gated chloride channels. PLoS One 2011; 6:e21970. [PMID: 21789198 PMCID: PMC3138761 DOI: 10.1371/journal.pone.0021970] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2011] [Accepted: 06/14/2011] [Indexed: 11/29/2022] Open
Abstract
Together, acid-sensing ion channels (ASICs) and epithelial sodium channels (ENaC) constitute the majority of voltage-independent sodium channels in mammals. ENaC is regulated by a chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR). Here we show that ASICs were reversibly inhibited by activation of GABAA receptors in murine hippocampal neurons. This inhibition of ASICs required opening of the chloride channels but occurred with both outward and inward GABAA receptor-mediated currents. Moreover, activation of the GABAA receptors modified the pharmacological features and kinetic properties of the ASIC currents, including the time course of activation, desensitization and deactivation. Modification of ASICs by open GABAA receptors was also observed in both nucleated patches and outside-out patches excised from hippocampal neurons. Interestingly, ASICs and GABAA receptors interacted to regulate synaptic plasticity in CA1 hippocampal slices. The activation of glycine receptors, which are similar to GABAA receptors, also modified ASICs in spinal neurons. We conclude that GABAA receptors and glycine receptors modify ASICs in neurons through mechanisms that require the opening of chloride channels.
Collapse
Affiliation(s)
- Xuanmao Chen
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Robarts Research Institute, University of Western Ontario, London, Ontario, Canada
| | - Paul Whissell
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Beverley A. Orser
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Anesthesia, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada
- Department of Anesthesia, University of Toronto, Toronto, Ontario, Canada
- * E-mail: (BAO); (JFM)
| | - John F. MacDonald
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Robarts Research Institute, University of Western Ontario, London, Ontario, Canada
- * E-mail: (BAO); (JFM)
| |
Collapse
|
245
|
Krishnan GP, Bazhenov M. Ionic dynamics mediate spontaneous termination of seizures and postictal depression state. J Neurosci 2011; 31:8870-82. [PMID: 21677171 PMCID: PMC3163257 DOI: 10.1523/jneurosci.6200-10.2011] [Citation(s) in RCA: 110] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2010] [Revised: 03/30/2011] [Accepted: 04/20/2011] [Indexed: 11/21/2022] Open
Abstract
Epileptic seizures are characterized by periods of recurrent, highly synchronized activity that spontaneously terminates, followed by postictal state when neuronal activity is generally depressed. The mechanisms for spontaneous seizure termination and postictal depression remain poorly understood. Using a realistic computational model, we demonstrate that termination of seizure and postictal depression state may be mediated by dynamics of the intracellular and extracellular ion concentrations. Spontaneous termination was linked to progressive increase of intracellular sodium concentration mediated by activation of sodium channels during highly active epileptic state. In contrast, an increase of intracellular chloride concentration extended seizure duration making possible long-lasting epileptic activity characterized by multiple transitions between tonic and clonic states. After seizure termination, the extracellular potassium was reduced below baseline, resulting in postictal depression. Our study suggests that the coupled dynamics of sodium, potassium, and chloride ions play a critical role in the development and termination of seizures. Findings from this study could help identify novel therapeutics for seizure disorder.
Collapse
Affiliation(s)
- Giri P. Krishnan
- Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, California 92521
| | - Maxim Bazhenov
- Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, California 92521
| |
Collapse
|
246
|
Lv RJ, He JS, Fu YH, Zhang YQ, Shao XQ, Wu LW, Lu Q, Jin LR, Liu H. ASIC1a polymorphism is associated with temporal lobe epilepsy. Epilepsy Res 2011; 96:74-80. [PMID: 21664108 DOI: 10.1016/j.eplepsyres.2011.05.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 04/23/2011] [Accepted: 05/01/2011] [Indexed: 01/23/2023]
Abstract
Recent in vitro and in vivo data show that acid-sensing ion channel 1a (ASIC1a) activation enhances neuronal excitability in the hippocampus and neocortex, indicating that ASIC1a might play a role in the generation and maintenance of epileptic seizures. The aim of this study was to investigate association of the ASIC1a gene with temporal lobe epilepsy (TLE) for the first time. Six tag single-nucleotide polymorphisms (SNPs) of the ASIC1a gene were selected and genotyped using polymerase chain reaction-restriction fragment length polymorphism in 560 TLE patients and 401 healthy controls. There was a significant allelic and genotypic association between rs844347:A>C and TLE compared with controls. The rs844347-A allele frequency was 88.1% in the patients and 83.0% in control subjects (OR=1.516, 95% CI 1.142-2.013, p=0.004). Furthermore, the haplotype analysis revealed a significant association with TLE. The results of this study demonstrate for the first time an association between an ASC1a variant allele and TLE in a Han Chinese population.
Collapse
Affiliation(s)
- Rui-Juan Lv
- Department of Neurology, Beijing Tiantan Hospital, Capital Medical University, Beijing, PR China
| | | | | | | | | | | | | | | | | |
Collapse
|
247
|
Sun X, Cao YB, Hu LF, Yang YP, Li J, Wang F, Liu CF. ASICs mediate the modulatory effect by paeoniflorin on alpha-synuclein autophagic degradation. Brain Res 2011; 1396:77-87. [DOI: 10.1016/j.brainres.2011.04.011] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 04/02/2011] [Accepted: 04/05/2011] [Indexed: 11/28/2022]
|
248
|
Hayashi K, Ueshima S, Ouchida M, Mashimo T, Nishiki T, Sendo T, Serikawa T, Matsui H, Ohmori I. Therapy for hyperthermia-induced seizures in Scn1a mutant rats. Epilepsia 2011; 52:1010-7. [PMID: 21480876 DOI: 10.1111/j.1528-1167.2011.03046.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
PURPOSE Mutations in the SCN1A gene, which encodes the α1 subunit of voltage-gated sodium channels, cause generalized epilepsy with febrile seizures plus (GEFS+) and severe myoclonic epilepsy of infancy (SMEI). N1417H-Scn1a mutant rats are considered to be an animal model of human FS+ or GEFS+. To assess the pharmacologic validity of this model, we compared the efficacies of eight different antiepileptic drugs (AEDs) for the treatment of hyperthermia-induced seizures using N1417H-Scn1a mutant rats. METHODS AEDs used in this study included valproate, carbamazepine (CBZ), phenobarbital, gabapentin, acetazolamide, diazepam (DZP), topiramate, and potassium bromide (KBr). The effects of these AEDs were evaluated using the hot water model, which is a model of experimental FS. Five-week-old rats were pretreated with each AED and immersed in water at 45°C to induce hyperthermia-induced seizures. The seizure manifestations and video-electroencephalographic recordings were evaluated. Furthermore, the effects of each AED on motor coordination and balance were assessed using the balance-beam test. KEY FINDINGS KBr significantly reduced seizure durations, and its anticonvulsant effects were comparable to those of DZP. On the other hand, CBZ decreased the seizure threshold. In addition, DZP and not KBr showed significant impairment in motor coordination and balance. SIGNIFICANCE DZP and KBr showed potent inhibitory effects against hyperthermia-induced seizures in the Scn1a mutant rats, whereas CBZ exhibited adverse effects. These responses to hyperthermia-induced seizures were similar to those in patients with GEFS+ and SMEI. N1417H-Scn1a mutant rats may, therefore, be useful for testing the efficacy of new AEDs against FS in GEFS+ and SMEI patients.
Collapse
Affiliation(s)
- Keiichiro Hayashi
- Department of Physiology, Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | | | | | | | | | | | | | | | | |
Collapse
|
249
|
Depolarizing actions of GABA in immature neurons depend neither on ketone bodies nor on pyruvate. J Neurosci 2011; 31:34-45. [PMID: 21209187 DOI: 10.1523/jneurosci.3314-10.2011] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
GABA depolarizes immature neurons because of a high [Cl(-)](i) and orchestrates giant depolarizing potential (GDP) generation. Zilberter and coworkers (Rheims et al., 2009; Holmgren et al., 2010) showed recently that the ketone body metabolite DL-3-hydroxybutyrate (DL-BHB) (4 mM), lactate (4 mM), or pyruvate (5 mM) shifted GABA actions to hyperpolarizing, suggesting that the depolarizing effects of GABA are attributable to inadequate energy supply when glucose is the sole energy source. We now report that, in rat pups (postnatal days 4-7), plasma D-BHB, lactate, and pyruvate levels are 0.9, 1.5, and 0.12 mM, respectively. Then, we show that DL-BHB (4 mM) and pyruvate (200 μM) do not affect (i) the driving force for GABA(A) receptor-mediated currents (DF(GABA)) in cell-attached single-channel recordings, (2) the resting membrane potential and reversal potential of synaptic GABA(A) receptor-mediated responses in perforated patch recordings, (3) the action potentials triggered by focal GABA applications, or (4) the GDPs determined with electrophysiological recordings and dynamic two-photon calcium imaging. Only very high nonphysiological concentrations of pyruvate (5 mM) reduced DF(GABA) and blocked GDPs. Therefore, DL-BHB does not alter GABA signals even at the high concentrations used by Zilberter and colleagues, whereas pyruvate requires exceedingly high nonphysiological concentrations to exert an effect. There is no need to alter conventional glucose enriched artificial CSF to investigate GABA signals in the developing brain.
Collapse
|
250
|
Tolner EA, Hochman DW, Hassinen P, Otáhal J, Gaily E, Haglund MM, Kubová H, Schuchmann S, Vanhatalo S, Kaila K. Five percent CO₂ is a potent, fast-acting inhalation anticonvulsant. Epilepsia 2011; 52:104-14. [PMID: 20887367 PMCID: PMC3017646 DOI: 10.1111/j.1528-1167.2010.02731.x] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
PURPOSE CO₂ has been long recognized for its anticonvulsant properties. We aimed to determine whether inhaling 5% CO₂ can be used to suppress seizures in epilepsy patients. The effect of CO₂ on cortical epileptic activity accompanying behavioral seizures was studied in rats and nonhuman primates, and based on these data, preliminary tests were carried out in humans. METHODS In freely moving rats, cortical afterdischarges paralleled by myoclonic convulsions were evoked by sensorimotor cortex stimulation. Five percent CO₂ was applied for 5 min, 3 min before stimulation. In macaque monkeys, hypercarbia was induced by hypoventilation while seizure activity was electrically or chemically evoked in the sensorimotor cortex. Seven patients with drug-resistant partial epilepsy were examined with video-EEG (electroencephalography) and received 5% CO₂ in medical carbogen shortly after electrographic seizure onset. RESULTS In rats, 5% CO₂ strongly suppressed cortical afterdischarges, by approximately 75%, whereas responses to single-pulse stimulation were reduced by about 15% only. In macaques, increasing pCO₂) from 37 to 44-45 mm Hg (corresponding to inhalation of 5% CO₂ or less) suppressed stimulation-induced cortical afterdischarges by about 70% and single, bicuculline-induced epileptiform spikes by approximately 25%. In a pilot trial carried out in seven patients, a rapid termination of electrographic seizures was seen despite the fact that the application of 5% CO₂ was started after seizure generalization. CONCLUSIONS Five percent CO₂ has a fast and potent anticonvulsant action. The present data suggest that medical carbogen with 5% CO₂ can be used for acute treatment to suppress seizures in epilepsy patients.
Collapse
Affiliation(s)
- Else A. Tolner
- Department of Biological and Environmental Sciences, University of Helsinki, Finland
| | - Daryl W. Hochman
- Departments of Surgery (Surgical Sciences) and Pharmacology & Cancer Biology, Duke University Medical Center, Durham, North Carolina, USA
| | - Pekka Hassinen
- Helstiinki University Central Hospital, University of Helsinki, Finland
| | - Jakub Otáhal
- Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Eija Gaily
- Helstiinki University Central Hospital, University of Helsinki, Finland
| | - Michael M. Haglund
- Departments of Surgery (Neurosurgery) and Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Hana Kubová
- Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Sebastian Schuchmann
- Neuroscience Research Center, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Sampsa Vanhatalo
- Helstiinki University Central Hospital, University of Helsinki, Finland
| | - Kai Kaila
- Department of Biological and Environmental Sciences, University of Helsinki, Finland
- Neuroscience Center, University of Helsinki, Finland
| |
Collapse
|