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Mehboob R, Marchenkova A, van den Maagdenberg AMJM, Nistri A. Overexpressed Na V 1.7 Channels Confer Hyperexcitability to in vitro Trigeminal Sensory Neurons of Ca V 2.1 Mutant Hemiplegic Migraine Mice. Front Cell Neurosci 2021; 15:640709. [PMID: 34113237 PMCID: PMC8185157 DOI: 10.3389/fncel.2021.640709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 04/09/2021] [Indexed: 11/21/2022] Open
Abstract
Trigeminal sensory neurons of transgenic knock-in (KI) mice expressing the R192Q missense mutation in the α1A subunit of neuronal voltage-gated CaV2.1 Ca2+ channels, which leads to familial hemiplegic migraine type 1 (FHM1) in patients, exhibit a hyperexcitability phenotype. Here, we show that the expression of NaV1.7 channels, linked to pain states, is upregulated in KI primary cultures of trigeminal ganglia (TG), as shown by increased expression of its α1 subunit. In the majority of TG neurons, NaV1.7 channels are co-expressed with ATP-gated P2X3 receptors (P2X3R), which are important nociceptive sensors. Reversing the trigeminal phenotype with selective CaV2.1 channel inhibitor ω-agatoxin IVA inhibited NaV1.7 overexpression. Functionally, KI neurons revealed a TTX-sensitive inward current of larger amplitude that was partially inhibited by selective NaV1.7 blocker Tp1a. Under current-clamp condition, Tp1a raised the spike threshold of both wild-type (WT) and KI neurons with decreased firing rate in KI cells. NaV1.7 activator OD1 accelerated firing in WT and KI neurons, a phenomenon blocked by Tp1a. Enhanced expression and function of NaV1.7 channels in KI TG neurons resulted in higher excitability and facilitated nociceptive signaling. Co-expression of NaV1.7 channels and P2X3Rs in TGs may explain how hypersensitivity to local stimuli can be relevant to migraine.
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Affiliation(s)
- Riffat Mehboob
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy.,Research Unit, Faculty of Allied Health Sciences, University of Lahore, Lahore, Pakistan
| | - Anna Marchenkova
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Arn M J M van den Maagdenberg
- Department of Neurology, Leiden University Medical Center, Leiden, Netherlands.,Department of Human Genetics, University Medical Center, Leiden, Netherlands
| | - Andrea Nistri
- Department of Neuroscience, International School for Advanced Studies (SISSA), Trieste, Italy
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Weissmann C, Albanese AA, Contreras NE, Gobetto MN, Castellanos LCS, Uchitel OD. Ion channels and pain in Fabry disease. Mol Pain 2021; 17:17448069211033172. [PMID: 34284652 PMCID: PMC8299890 DOI: 10.1177/17448069211033172] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/24/2021] [Accepted: 06/28/2021] [Indexed: 12/29/2022] Open
Abstract
Fabry disease (FD) is a progressive, X-linked inherited disorder of glycosphingolipid metabolism due to deficient or absent lysosomal α-galactosidase A (α-Gal A) activity which results in progressive accumulation of globotriaosylceramide (Gb3) and related metabolites. One prominent feature of Fabry disease is neuropathic pain. Accumulation of Gb3 has been documented in dorsal root ganglia (DRG) as well as other neurons, and has lately been associated with the mechanism of pain though the pathophysiology is still unclear. Small fiber (SF) neuropathy in FD differs from other entities in several aspects related to the perception of pain, alteration of fibers as well as drug therapies used in the practice with patients, with therapies far from satisfying. In order to develop better treatments, more information on the underlying mechanisms of pain is needed. Research in neuropathy has gained momentum from the development of preclinical models where different aspects of pain can be modelled and further analyzed. This review aims at describing the different in vitro and FD animal models that have been used so far, as well as some of the insights gained from their use. We focus especially in recent findings associated with ion channel alterations -that apart from the vascular alterations-, could provide targets for improved therapies in pain.
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Affiliation(s)
- Carina Weissmann
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET) and Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
| | - Adriana A Albanese
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET) and Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
| | - Natalia E Contreras
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET) and Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
| | - María N Gobetto
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET) and Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
| | - Libia C Salinas Castellanos
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET) and Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
| | - Osvaldo D Uchitel
- Instituto de Fisiología, Biología Molecular y Neurociencias (IFIBYNE-UBA-CONICET) and Departamento de Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
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Parisi P, Paolino MC, Raucci U, Della Vecchia N, Belcastro V, Villa MP, Striano P. Ictal Epileptic Headache: When Terminology Is Not a Moot Question. Front Neurol 2019; 10:785. [PMID: 31396147 PMCID: PMC6664028 DOI: 10.3389/fneur.2019.00785] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2018] [Accepted: 07/08/2019] [Indexed: 11/13/2022] Open
Abstract
The relationship between headache and epilepsy is complex and despite the nature of this association is not yet clear. In the last few years, it has been progressively introduced the concept of the “ictal epileptic headache” that was included in the recently revised International Classification of Headaches Disorders 3rd edition (ICHD-3-revised). The diagnostic criteria for ictal epileptic headache (IEH) suggested in 2012 were quite restrictive thus leading to the underestimation of this phenomenon. However, these criteria have not yet been included into the ICHD-3 revision published in 2018, thus creating confusion among both, physicians and experts in this field. Here, we highlight the importance to strictly apply the original IEH criteria explaining the reasons through the analysis of the clinical, historical, epidemiological and pathophysiological characteristics of the IEH itself. In addition, we discuss the issues related to the neurophysiopathological link between headache and epilepsy as well as to the classification of these epileptic events as “autonomic seizure.”
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Affiliation(s)
- Pasquale Parisi
- Chair of Pediatrics, Child Neurology, NESMOS Department, Faculty of Medicine and Psychology, Sapienza University, Sant'Andrea Hospital, Rome, Italy
| | - Maria Chiara Paolino
- Chair of Pediatrics, Child Neurology, NESMOS Department, Faculty of Medicine and Psychology, Sapienza University, Sant'Andrea Hospital, Rome, Italy
| | - Umberto Raucci
- Pediatric Emergency Department, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy
| | | | - Vincenzo Belcastro
- Neurology Unit, Department of Neuroscience, Sant'Anna Hospital, Como, Italy
| | - Maria Pia Villa
- Chair of Pediatrics, Child Neurology, NESMOS Department, Faculty of Medicine and Psychology, Sapienza University, Sant'Andrea Hospital, Rome, Italy
| | - Pasquale Striano
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health, University of Genoa, Genova, Italy.,Paediatric Neurology and Muscular Diseases Unit, G. Gaslini' Institute, Genova, Italy
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Marchenkova A, Vilotti S, Ntamati N, van den Maagdenberg AM, Nistri A. Inefficient constitutive inhibition of P2X3 receptors by brain natriuretic peptide system contributes to sensitization of trigeminal sensory neurons in a genetic mouse model of familial hemiplegic migraine. Mol Pain 2016; 12:12/0/1744806916646110. [PMID: 27175010 PMCID: PMC4955999 DOI: 10.1177/1744806916646110] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Accepted: 03/23/2016] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND On trigeminal ganglion neurons, pain-sensing P2X3 receptors are constitutively inhibited by brain natriuretic peptide via its natriuretic peptide receptor-A. This inhibition is associated with increased P2X3 serine phosphorylation and receptor redistribution to non-lipid raft membrane compartments. The natriuretic peptide receptor-A antagonist anantin reverses these effects. We studied whether P2X3 inhibition is dysfunctional in a genetic familial hemiplegic migraine type-1 model produced by introduction of the human pathogenic R192Q missense mutation into the mouse CACNA1A gene (knock-in phenotype). This model faithfully replicates several properties of familial hemiplegic migraine type-1, with gain-of-function of CaV2.1 Ca(2+) channels, raised levels of the algogenic peptide calcitonin gene-related peptide, and enhanced activity of P2X3 receptors in trigeminal ganglia. RESULTS In knock-in neurons, anantin did not affect P2X3 receptor activity, membrane distribution, or serine phosphorylation level, implying ineffective inhibition by the constitutive brain natriuretic peptide/natriuretic peptide receptor-A pathway. However, expression and functional properties of this pathway remained intact together with its ability to downregulate TRPV1 channels. Reversing the familial hemiplegic migraine type-1 phenotype with the CaV2.1-specific antagonist, ω-agatoxin IVA restored P2X3 activity to wild-type level and enabled the potentiating effects of anantin again. After blocking calcitonin gene-related peptide receptors, P2X3 receptors exhibited wild-type properties and were again potentiated by anantin. CONCLUSIONS P2X3 receptors on mouse trigeminal ganglion neurons are subjected to contrasting modulation by inhibitory brain natriuretic peptide and facilitatory calcitonin gene-related peptide that both operate via complex intracellular signaling. In the familial hemiplegic migraine type-1 migraine model, the action of calcitonin gene-related peptide appears to prevail over brain natriuretic peptide, thus suggesting that peripheral inhibition of P2X3 receptors becomes insufficient and contributes to trigeminal pain sensitization.
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Affiliation(s)
- Anna Marchenkova
- Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Sandra Vilotti
- Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Niels Ntamati
- Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Arn Mjm van den Maagdenberg
- Department of Neurology, Leiden University Medical Centre, Leiden, the Netherlands Department of Human Genetics, Leiden University Medical Centre, Leiden, the Netherlands
| | - Andrea Nistri
- Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
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Abstract
Primary headache and attention-deficit/hyperactivity disorder (ADHD) are common disorders in children and adolescences, frequently associated to severe cognitive, emotional, and behavioral impairments. They both are a disabling condition with consequences on family and child's quality of life. Literature data on their association are contrasting. Dopaminergic system dysfunction, brain iron deficiency, and sleep disturbance should be considered to better understand headache and ADHD overlap. In this review, we analyze the complex association between these two diseases and the potential impact on child neurodevelopment.
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Abstract
Chronic pain is a major therapeutic problem as the current treatment options are unsatisfactory with low efficacy and deleterious side effects. Voltage-gated Ca2+ channels (VGCCs), which are multi-complex proteins consisting of α1, β, γ, and α2δ subunits, play an important role in pain signaling. These channels are involved in neurogenic inflammation, excitability, and neurotransmitter release in nociceptors. It has been previously shown that N-type VGCCs (Cav2.2) are a major pain target. U.S. FDA approval of three Cav2.2 antagonists, gabapentin, pregabalin, and ziconotide, for chronic pain underlies the importance of this channel subtype. Also, there has been increasing evidence that L-type (Cav1.2) or T-type (Cav3.2) VGCCs may be involved in pain signaling and chronic pain. In order to develop novel pain therapeutics and to understand the role of VGCC subtypes, discovering subtype selective VGCC inhibitors or methods that selectively target the inhibitor into nociceptors would be essential. This review describes the various VGCC subtype inhibitors and the potential of utilizing VGCC subtypes as targets of chronic pain. Development of VGCC subtype inhibitors and targeting them into nociceptors will contribute to a better understanding of the roles of VGCC subtypes in pain at a spinal level as well as development of a novel class of analgesics for chronic pain.
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Affiliation(s)
- Seungkyu Lee
- F. M. Kirby Neurobiology Center, Children's Hospital Boston, Boston MA 02115 USA; ; Department of Neurobiology, Harvard Medical School, Boston MA 02115 USA
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Abstract
In this chapter, we review the principal astrocyte functions and the interactions between neurons and astrocytes. We then address how the experimentally observed functions have been verified in computational models and review recent experimental literature on astrocyte-neuron interactions. Benefits of computational neuroscience work are highlighted through selected studies with neurons and astrocytes by analyzing the existing models qualitatively and assessing the relevance of these models to experimental data. Common strategies to mathematical modeling and computer simulation in neuroscience are summarized for the nontechnical reader. The astrocyte-neuron interactions are then further illustrated by examples of some neurological and neurodegenerative diseases, where the miscommunication between glia and neurons is found to be increasingly important.
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Affiliation(s)
- Marja-Leena Linne
- Computational Neuroscience Group, Department of Signal Processing, Tampere University of Technology, Tampere, Finland
| | - Tuula O Jalonen
- Department of Physiology and Neuroscience, St. George's University, School of Medicine, Grenada, West Indies
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Costa C, Tozzi A, Rainero I, Cupini LM, Calabresi P, Ayata C, Sarchielli P. Cortical spreading depression as a target for anti-migraine agents. J Headache Pain 2013; 14:62. [PMID: 23879550 PMCID: PMC3728002 DOI: 10.1186/1129-2377-14-62] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Accepted: 07/08/2013] [Indexed: 12/18/2022] Open
Abstract
Spreading depression (SD) is a slowly propagating wave of neuronal and glial depolarization lasting a few minutes, that can develop within the cerebral cortex or other brain areas after electrical, mechanical or chemical depolarizing stimulations. Cortical SD (CSD) is considered the neurophysiological correlate of migraine aura. It is characterized by massive increases in both extracellular K⁺ and glutamate, as well as rises in intracellular Na⁺ and Ca²⁺. These ionic shifts produce slow direct current (DC) potential shifts that can be recorded extracellularly. Moreover, CSD is associated with changes in cortical parenchymal blood flow. CSD has been shown to be a common therapeutic target for currently prescribed migraine prophylactic drugs. Yet, no effects have been observed for the antiepileptic drugs carbamazepine and oxcarbazepine, consistent with their lack of efficacy on migraine. Some molecules of interest for migraine have been tested for their effect on CSD. Specifically, blocking CSD may play an enabling role for novel benzopyran derivative tonabersat in preventing migraine with aura. Additionally, calcitonin gene-related peptide (CGRP) antagonists have been recently reported to inhibit CSD, suggesting the contribution of CGRP receptor activation to the initiation and maintenance of CSD not only at the classic vascular sites, but also at a central neuronal level. Understanding what may be lying behind this contribution, would add further insights into the mechanisms of actions for "gepants", which may be pivotal for the effectiveness of these drugs as anti-migraine agents. CSD models are useful tools for testing current and novel prophylactic drugs, providing knowledge on mechanisms of action relevant for migraine.
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Affiliation(s)
- Cinzia Costa
- Neurologic Clinic, Department of Public Health and Medical and Surgical Specialties, University of Perugia, Ospedale Santa Maria della Misericordia, Sant'Andrea delle Fratte, 06132, Perugia, Italy
- Fondazione Santa Lucia I.R.C.C.S., Via del Fosso di Fiorano, 00143, Rome, Italy
| | - Alessandro Tozzi
- Neurologic Clinic, Department of Public Health and Medical and Surgical Specialties, University of Perugia, Ospedale Santa Maria della Misericordia, Sant'Andrea delle Fratte, 06132, Perugia, Italy
- Fondazione Santa Lucia I.R.C.C.S., Via del Fosso di Fiorano, 00143, Rome, Italy
| | - Innocenzo Rainero
- Neurology II, Department of Neuroscience, University of Torino, Ospedale Molinette, Via Cherasco 15, 10126, Turin, Italy
| | | | - Paolo Calabresi
- Neurologic Clinic, Department of Public Health and Medical and Surgical Specialties, University of Perugia, Ospedale Santa Maria della Misericordia, Sant'Andrea delle Fratte, 06132, Perugia, Italy
- Fondazione Santa Lucia I.R.C.C.S., Via del Fosso di Fiorano, 00143, Rome, Italy
| | - Cenk Ayata
- Neurovascular Research Lab., Department of Radiology, Stroke Service and Neuroscience Intensive Unit Department of Neurology Massachusetts Hospital, Harvard Medical School, 02115, Boston, MA, USA
| | - Paola Sarchielli
- Neurologic Clinic, Department of Public Health and Medical and Surgical Specialties, University of Perugia, Ospedale Santa Maria della Misericordia, Sant'Andrea delle Fratte, 06132, Perugia, Italy
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Lüthi A. The Adenosine Story Goes Ionic: CaV2.1-type Ca2+ Channels Identified as Effectors of Adenosine's Somnogenic Actions. Sleep 2013; 36:13-4. [DOI: 10.5665/sleep.2290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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Parisi P, Striano P, Negro A, Martelletti P, Belcastro V. Ictal epileptic headache: an old story with courses and appeals. J Headache Pain 2012; 13:607-13. [PMID: 23015297 PMCID: PMC3484263 DOI: 10.1007/s10194-012-0485-y] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Accepted: 09/13/2012] [Indexed: 11/27/2022] Open
Abstract
The term “ictal epileptic headache” has been recently proposed to classify the clinical picture in which headache is the isolated ictal symptom of a seizure. There is emerging evidence from both basic and clinical neurosciences that cortical spreading depression and an epileptic focus may facilitate each other, although with a different degree of efficiency. This review address the long history which lead to the 'migralepsy' concept to the new emerging pathophysiological aspects, and clinical and electroencephalography evidences of ictal epileptic headache. Here, we review and discuss the common physiopathology mechanisms and the historical aspects underlying the link between headache and epilepsy. Either experimental or clinical measures are required to better understand this latter relationship: the development of animal models, molecular studies defining more precise genotype/phenotype correlations as well as multicenter clinical studies with revision of clinical criteria for headache-/epilepsy-related disorders represent the start of future research. Therefore, the definition of ictal epileptic headache should be used to classify the rare events in which headache is the only manifestation of a seizure. Finally, using our recently published criteria, we will be able to clarify if ictal epileptic headache represents an underestimated phenomenon or not.
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Affiliation(s)
- Pasquale Parisi
- NESMOS Department, Faculty of Medicine and Psychology, Child Neurology, Headache Paediatric Center, Paediatric Sleep Disorders, Chair of Paediatrics, Sapienza University, c/o Sant'Andrea Hospital, Via di Grottarossa, 1035-1039, Rome, Italy.
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Gandini MA. Channeling headache: novel findings in the study of Ca(2+)-channels and FHM-1. Channels (Austin) 2012; 6:414-5. [PMID: 22991044 DOI: 10.4161/chan.22146] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Familial hemiplegic migraine type 1 (FMH-1) is a rare form of migraine with aura, which is characterized by transient hemiparesis, sensory loss and visual disturbances. This monogenic disease shares many common features with classic migraine, suggesting a similar molecular pathophysiology. Migraine is triggered by activation and sensitization of the trigeminovascular system, specifically the trigeminal nociceptive afferents innervating the meninges. Aura migraine is associated with cortical spreading depression (CSD), which is a short-lasting intense wave of neuronal and glial cell depolarization that slowly progresses over the cortex and is followed by long-lasting neuronal activity depression.
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Affiliation(s)
- María A Gandini
- Department of Cell Biology, Center for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav-IPN), Mexico City, Mexico.
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Garza-López E, Sandoval A, González-Ramírez R, Gandini MA, Van den Maagdenberg A, De Waard M, Felix R. Familial hemiplegic migraine type 1 mutations W1684R and V1696I alter G protein-mediated regulation of Ca(V)2.1 voltage-gated calcium channels. Biochim Biophys Acta Mol Basis Dis 2012; 1822:1238-46. [PMID: 22549042 DOI: 10.1016/j.bbadis.2012.04.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Revised: 04/10/2012] [Accepted: 04/12/2012] [Indexed: 12/13/2022]
Abstract
Familial hemiplegic migraine type 1 (FHM-1) is a monogenic form of migraine with aura that is characterized by recurrent attacks of a typical migraine headache with transient hemiparesis during the aura phase. In a subset of patients, additional symptoms such as epilepsy and cerebellar ataxia are part of the clinical phenotype. FHM-1 is caused by missense mutations in the CACNA1A gene that encodes the pore-forming subunit of Ca(V)2.1 voltage-gated Ca(2+) channels. Although the functional effects of an increasing number of FHM-1 mutations have been characterized, knowledge on the influence of most of these mutations on G protein regulation of channel function is lacking. Here, we explored the effects of G protein-dependent modulation on mutations W1684R and V1696I which cause FHM-1 with and without cerebellar ataxia, respectively. Both mutations were introduced into the human Ca(V)2.1α(1) subunit and their functional consequences investigated after heterologous expression in human embryonic kidney 293 (HEK-293) cells using patch-clamp recordings. When co-expressed along with the human μ-opioid receptor, application of the agonist [d-Ala2, N-MePhe4, Gly-ol]-enkephalin (DAMGO) inhibited currents through both wild-type (WT) and mutant Ca(V)2.1 channels, which is consistent with the known modulation of these channels by G protein-coupled receptors. Prepulse facilitation, which is a way to characterize the relief of direct voltage-dependent G protein regulation, was reduced by both FHM-1 mutations. Moreover, the kinetic analysis of the onset and decay of facilitation showed that the W1684R and V1696I mutations affect the apparent dissociation and reassociation rates of the Gβγ dimer from the channel complex, suggesting that the G protein-Ca(2+) channel affinity may be altered by the mutations. These biophysical studies may shed new light on the pathophysiology underlying FHM-1.
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