A novel missense ATP1A2 mutation in a Finnish family with familial hemiplegic migraine type 2

Familial hemiplegic migraine (FHM), a rare autosomal dominant subtype of migraine with aura, has been linked to two chromosomal loci, 19p13 and 1q23. Mutations in the Na⁺,K⁺-ATPase 2 subunit gene, ATP1A2, on 1q23 have recently been shown to cause familial hemiplegic migraine type 2 (FHM2). We sequenced the coding regions of this gene in a Finnish chromosome 1q23-linked FHM family with associated symptoms such as coma and identified a novel A1033G mutation in exon 9. This mutation results in a threonine-to-alanine substitution at codon 345. This residue is located in a highly conserved N-terminal region of the M4–5 loop of the Na⁺,K⁺-ATPase. Furthermore, the T345A mutation co-segregated with the disorder in our family and was not present in 132 healthy Finnish control individuals. For these reasons it is most likely the FHM-causing mutation in this family.     

A G301R Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase mutation causes familial hemiplegic migraine type 2 with cerebellar signs

Familial hemiplegic migraine (FHM) is an autosomal dominant subtype of migraine with hemiparesis during the aura. In over 50% of cases the causative gene is CACNA1A (FHM1), which in some cases produces a phenotype with cerebellar signs, including ataxia and nystagmus. Recently, mutations in ATP1A2 on chromosome 1q23 encoding a Na⁺/K⁺-ATPase subunit were identified in four families (FHM2). We now describe an FHM2 pedigree with a fifth ATP1A2 mutation coding for a G301R substitution. The phenotype was particularly severe and included hemiplegic migraine, seizure, prolonged coma, elevated temperature, sensory deficit, and transient or permanent cerebellar signs, such as ataxia, nystagmus, and dysarthria. A mild crossed cerebellar diaschisis during an attack further supported the clinical evidence of a cerebellar deficit. This is the first report suggesting cerebellar involvement in FHM2. A possible role for CACNA1A in producing the phenotype in this family was excluded by linkage studies to the FHM1 locus. The study of this family suggests that the absence of cerebellar signs may not be a reliable indicator to clinically differentiate FHM2 from FHM1.     

Androgenic suppression of spreading depression in familial hemiplegic migraine type 1 mutant mice

Familial hemiplegic migraine type 1 (FHM1), a severe migraine with aura variant, is caused by mutations in the CACNA1A gene. Mutant mice carrying the FHM1 R192Q mutation exhibit increased propensity for cortical spreading depression (CSD), a propagating wave of neuroglial depolarization implicated in migraine aura. The CSD phenotype is stronger in female R192Q mutants and diminishes after ovariectomy. Here, we show that orchiectomy reciprocally increases CSD susceptibility in R192Q mutant mice. Chronic testosterone replacement restores CSD susceptibility by an androgen receptor‐dependent mechanism. Hence, androgens modulate genetically‐enhanced CSD susceptibility and may provide a novel prophylactic target for migraine. Ann Neurol 2009;66:564–568     

Gabapentin suppresses cortical spreading depression susceptibility

Cortical spreading depression (CSD) is an intense depolarization wave implicated in the pathophysiology of brain injury states and migraine aura. As Ca_v2.1 channels modulate CSD susceptibility, we tested gabapentin, which inhibits Ca_v2.1 through high-affinity binding to its α₂δ subunit, on CSD susceptibility in anesthetized rats. Gabapentin, 100 or 200 mg/kg, elevated the electrical threshold for CSD and diminished recurrent CSDs evoked by topical KCl, when administered 1 hour before testing. With its favorable safety and tolerability profile, gabapentin may have a role in suppression of injury depolarizations in stroke, intracranial hemorrhage, and traumatic brain injury.     

Neutralization of a unique, negatively-charged residue in the voltage sensor of KV7.2 subunits in a sporadic case of benign familial neonatal seizures

Benign Familial Neonatal Seizures (BFNS) is a rare, autosomal-dominant epilepsy of the newborn caused by mutations in K_v7.2 (KCNQ2) or K_v7.3 (KCNQ3) genes encoding for neuronal potassium (K⁺) channel subunits. In this study, we describe a sporadic case of BFNS; the affected child carried heterozygous missense mutations in both K_v7.2 (D212G) and K_v7.3 (P574S) alleles. Electrophysiological experiments revealed that the K_v7.2 D212G substitution, neutralizing a unique negatively-charged residue in the voltage sensor of K_v7.2 subunits, altered channel gating, leading to a marked destabilization of the open state, a result consistent with structural analysis of the K_v7.2 subunit, suggesting a possible pathogenetic role for BFNS of this K_v7.2 mutation. By contrast, no significant functional changes appeared to be prompted by the K_v7.3 P574S substitution. Computational modelling experiments in CA1 pyramidal cells revealed that the gating changes introduced by the K_v7.2 D212G increased cell firing frequency, thereby triggering the neuronal hyperexcitability which underlies the observed neonatal epileptic condition.     

Potassium channels: a review of broadening therapeutic possibilities for neurological diseases

Potassium (K⁺) channels are encoded by approximately 80 genes in mammals. They are expressed in many tissues and have diverse physiological roles. Human K⁺ channels are divided mainly into calcium (Ca²⁺)-activated (K_Ca), inward-rectifying (K_IR), two-pore (K_2P), and voltage-gated (K_v) channels. The K_v channels form the largest family, with approximately 40 genes. Owing to their involvement in many diseases and their specific expression patterns and physiological roles, K⁺ channels present an attractive target for the development of new therapies. This review summarizes the physiological and pathophysiological roles of various potassium channels with respect to their therapeutic potential for disorders with a disturbed neuronal excitability such as epilepsy, migraine, neuropathic pain, or stroke.     

Curcumin inhibits glutamate release in nerve terminals from rat prefrontal cortex: possible relevance to its antidepressant mechanism

There is abundant evidence suggesting the relevance of glutamate to depression and antidepressant mechanisms. Curcumin, a major active compound of Curcuma longa, has been reported to have the biological function of antidepressant. The aim of the present study was to investigate the effect of curcumin on endogenous glutamate release in nerve terminals of rat prefrontal cortex and the underlying mechanisms. The results showed that curcumin inhibited the release of glutamate that was evoked by exposing synaptosomes to the K⁺ channel blocker 4-aminopyridine (4-AP). This phenomenon was blocked by the chelating the extracellular Ca²⁺ ions, and by the vesicular transporter inhibitor bafilomycin A1, but was insensitive to the glutamate transporter inhibitor DL-threo-β-benzyl-oxyaspartate (DL-TBOA). Further experiments demonstrated that curcumin decreased depolarization-induced increase in [Ca²⁺]_C, whereas it did not alter the resting membrane potential or 4-AP-mediated depolarization. Furthermore, the inhibitory effect of curcumin on evoked glutamate release was prevented by blocking the Ca_v2.2 (N-type) and Ca_v2.1 (P/Q-type) channels, but not by blocking intracellular Ca²⁺ release or Na⁺/Ca²⁺ exchange. These results suggest that curcumin inhibits evoked glutamate release from rat prefrontocortical synaptosomes by the suppression of presynaptic Ca_v2.2 and Ca_v2.1 channels. Additionally, we also found that the inhibitory effect of curcumin on 4-AP-evoked glutamate release was completely abolished by the clinically effective antidepressant fluoxetine. This suggests that curcumin and fluoxetine use a common intracellular mechanism to inhibit glutamate release from rat prefrontal cortex nerve terminals.     

Hemiplegic migraine type 2 caused by a novel variant within the P-type ATPase motif in ATP1A2 concomitant with a CACNA1A variant

BackgroundFamilial hemiplegic migraine (FHM) is an inherited autosomal dominant disorder characterized by migraine with reversible hemiplegia. FHM1 is caused by variants in CACNA1A, encoding a P/Q type neuronal voltage-gated calcium channel α subunit, which is also associated with episodic ataxia type 2 (EA2). FHM2 is associated with ATP1A2, which codes for an Na⁺/K⁺-ATPase isoform 2 subunit.Case presentationWe identified an FHM2 family, the mother and her daughter, with a novel variant in ATP1A2, p.Gly377Asp, located in a well-conserved P-type ATPase motif. Additionally, the mother harbored deletion in the CACNA1A, associated with EA2, but her daughter did not. The mother presented migraine with typical aura without motor deficit, whereas her daughter had migraine accompanied by recurrent motor deficit and altered consciousness. The additional CACNA1A deletion in the mother might serve as a modifier.ConclusionOur report emphasizes the importance of genetic analysis to diagnose neurological ion channel/transporter diseases.     

Interaction Between Ca<Subscript>v</Subscript>2.1α<Subscript>1</Subscript> and CaMKII in Ca<Subscript>v</Subscript>2.1α<Subscript>1</Subscript> Mutant Mice, <Emphasis Type="Italic">Rolling Nagoya</Emphasis>

It has been reported earlier that interactions between Ca_v2.1α₁ and calcium/calmodulin-dependent protein kinase II (CaMKII) in the presynaptic fraction and between the NMDA receptor subunit NR2B and CaMKII in the postsynaptic density (PSD) fraction are important for neuronal function. Ca_v2.1α₁, CaMKII, and NR2B are predominantly expressed in the hippocampus. To examine the above interactions and CaMKII activity in the hippocampal presynapse and PSD of Rolling Nagoya mice carrying a mutation in Ca_v2.1α₁ subunit, we performed immunoprecipitation and Western blot analyses. In the presynapse, the interaction between Ca_v2.1α₁ and CaMKII and the phosphorylation of CaMKII (at Thr286) and its substrate Synapsin I (at Ser603) were decreased in mutant mice compared to wild-type mice. In the PSD, a similar pattern was observed for the interaction between NR2B and CaMKII and the phosphorylation of CaMKII (at Thr286) and its substrate AMPA receptor subunit glutamate receptor 1 (at Ser831) between mutant and wild-type mice. Our data indicate that disruption of the interaction between Ca_v2.1α₁ and CaMKII may down-regulate presynaptic CaMKII activity and that Rolling Nagoya mice would be a useful model for examining presynaptic function.     

SCN1A/NaV1.1 channelopathies: Mechanisms in expression systems,animal models,and human iPSC models

Pathogenic SCN1A/Na_V1.1 mutations cause well‐defined epilepsies, including genetic epilepsy with febrile seizures plus (GEFS+) and the severe epileptic encephalopathy Dravet syndrome. In addition, they cause a severe form of migraine with aura, familial hemiplegic migraine. Moreover, SCN1A/Na_V1.1 variants have been inferred as risk factors in other types of epilepsy. We review here the advancements obtained studying pathologic mechanisms of SCN1A/Na_V1.1 mutations with experimental systems. We present results gained with in vitro expression systems, gene‐targeted animal models, and the induced pluripotent stem cell (iPSC) technology, highlighting advantages, limits, and pitfalls for each of these systems. Overall, the results obtained in the last two decades confirm that the initial pathologic mechanism of epileptogenic SCN1A/Na_V1.1 mutations is loss‐of‐function of Na_V1.1 leading to hypoexcitability of at least some types of γ‐aminobutyric acid (GABA)ergic neurons (including cortical and hippocampal parvalbumin‐positive and somatostatin‐positive ones). Conversely, more limited results point to Na_V1.1 gain‐of‐function for familial hemiplegic migraine (FHM) mutations. Behind these relatively simple pathologic mechanisms, an unexpected complexity has been observed, in part generated by technical issues in experimental studies and in part related to intrinsically complex pathophysiologic responses and remodeling, which yet remain to be fully disentangled.     

Importance of astrocytes for potassium ion (K+) homeostasis in brain and glial effects of K+ and its transporters on learning

Initial clearance of extracellular K⁺ ([K⁺]_o) following neuronal excitation occurs by astrocytic uptake, because elevated [K⁺]_o activates astrocytic but not neuronal Na⁺,K⁺-ATPases. Subsequently, astrocytic K⁺ is re-released via Kir4.1 channels after distribution in the astrocytic functional syncytium via gap junctions. The dispersal ensures widespread release, preventing renewed [K⁺]_o increase and allowing neuronal Na⁺,K⁺-ATPase-mediated re-uptake. Na⁺,K⁺-ATPase operation creates extracellular hypertonicity and cell shrinkage which is reversed by the astrocytic cotransporter NKCC1. Inhibition of Kir channels by activation of specific PKC isotypes may decrease syncytial distribution and enable physiologically occurring [K⁺]_o increases to open L-channels for Ca²⁺, activating [K⁺]_o-stimulated gliotransmitter release and regulating gap junctions. Learning is impaired when [K⁺]_o is decreased to levels mainly affecting astrocytic membrane potential or Na⁺,K⁺-ATPase or by abnormalities in its α2 subunit. It is enhanced by NKCC1-mediated ion and water uptake during the undershoot, reversing neuronal inactivity, but impaired in migraine with aura in which [K⁺]_o is highly increased. Vasopressin augments NKCC1 effects and facilitates learning. Enhanced myelination, facilitated by astrocytic-oligodendrocytic gap junctions also promotes learning.     

Ionic channel currents in cultured neurons from human cortex

Ionic channels in human cortical neurons have not been studied extensively. HCN-1 and HCN-1A cells, which recently were established as continuous cultures from human cortical tissue, have been shown by histochemical and immunochemical methods to exhibit a neuronal phenotype, but expression of functional ionic channels was not demonstrated. For the present study, HCN-1 and HCN-1A cells were cultured in Dulbecco's modified Eagle's medium with 15% fetal calf serum, in some cases supplemented with 10 ng/ml nerve growth factor, 10 μM forskolin, and 1 mM dibutyryl cyclic adenosine monophosphate to promote differentiation. Cells or membrane patches were voltage clamped using conventional patch clamp techniques. In HCN-1A cells, we identified a tetrodotoxin-sensitive Na⁺ current, two types of Ca²⁺ channel current, including L-type current and a second type that in some respects resembled N-type current, and four types of K⁺ current, including a delayed outward rectifier that showed voltage-dependent inactivation, two types of noninactivating Ca²⁺-activated K⁺ channels with slope conductances of 146 and 23 pS (K⁺ _iK⁺ _o 145 mM/5 mM), and less frequently, a noninactivating, intermediate conductance channel that was not sensitive to internal Ca²⁺. When HCN-1A cells were examined after 3 days of exposure to differentiating agents, pronounced morphological changes were evident but no differences in ionic currents were apparent. HCN-1 cells also exhibited K⁺ and Ca²⁺ channel currents, but Na⁺ currents were not detected in these cells. Our data provide additional evidence indicating a functional neuronal phenotype for HCN-1A cells, and represent the most comprehensive survey to date of the variety of ionic channels expressed by human cortical neurons. © 1993 Wiley-Liss, Inc.     

Spreading depression in human neocortical slices

Cortical spreading depression (CSD) occurrence has been suggested to be associated with seizures, migraine aura, head injury and brain ischemia-infarction. Only few studies identified CSD in human neocortical slices and no comprehensive study so far evaluated this phenomenon in human. Using the neocortical tissue excised for treatment of intractable epilepsy, we aimed to investigate CSD in human. CSD was induced by KCl injection and by modulating T-type Ca²⁺ currents in incubated human neocortical tissues in an interphase mode. The DC-fluctuations were recorded by inserting microelectrodes into different cortical layers. Local injection of KCl triggered single CSD that propagated at 3.1±0.1 mm/min. Repetitive CSD also occurred spontaneously during long lasting application (5 h) of the T-type Ca²⁺ channel blockers amiloride (50 μM) or NiCl₂ (10 μM) which was concomitant with a reversible extracellular potassium increase up to 50 mM. CSD could be blocked by the N-methyl- -aspartate receptor antagonist 2-amino-5-phosphonovaleric acid in all cases. The results demonstrate that modulation of the Ca²⁺ dynamics conditioned human neocortical slices and increased their susceptibility to generate CSD. Furthermore, these data indicate that glutamatergic pathway plays a role in CSD phenomenon in human.     

The ouabain-induced [Ca]i increase in leech Retzius neurones is mediated by voltage-dependent Ca channels

In leech Retzius neurones the inhibition of the Na⁺–K⁺ pump by ouabain causes an increase in the cytosolic free calcium concentration ([Ca²⁺]_i). To elucidate the mechanism of this increase we investigated the changes in [Ca²⁺]_i (measured by Fura-2) and in membrane potential that were induced by inhibiting the Na⁺–K⁺ pump in bathing solutions of different ionic composition. The results show that Na⁺–K⁺ pump inhibition induced a [Ca²⁺]_i increase only if the cells depolarized sufficiently in the presence of extracellular Ca²⁺. Specifically, the relationship between [Ca²⁺]_i and the membrane potential upon Na⁺–K⁺ pump inhibition closely matched the corresponding relationship upon activation of the voltage-dependent Ca²⁺ channels by raising the extracellular K⁺ concentration. It is concluded that the [Ca²⁺]_i increase caused by inhibiting the Na⁺–K⁺ pump in leech Retzius neurones is exclusively due to Ca²⁺ influx through voltage-dependent Ca²⁺ channels.     

Differential Stimulation of Noradrenaline Release by Reversal of the Na+/Ca2+ Exchanger and Depolarization in Chromaffin Cells

We compared the effectiveness of Ca²⁺ entering by Na⁺/Ca²⁺ exchange with that of Ca²⁺ entering by channels produced by membrane depolarization with K⁺ in inducing catecholamine release from bovine adrenal chromaffin cells. The Ca²⁺ influx through the Na⁺/Ca²⁺ exchanger was promoted by reversing the normal inward gradient of Na⁺ by preincubating the cells with ouabain to increase the intracellular Na⁺ and then removing Na⁺ from the external medium. In this way we were able to increase the cytosolic free Ca²⁺ concentration ([Ca²⁺]_c) by Na⁺/Ca²⁺ exchange to 325 ± 14 nM, which was similar to the rise in [Ca²⁺]_c observed upon depolarization with 35 mM K⁺ of cells not treated with ouabain. After incubating the cells with ouabain, K⁺ depolarization raised the [Ca²⁺]_c to 398 ± 31 nM, and the recovery of [Ca²⁺]_c to resting levels was significantly slower. Reversal of the Na⁺ gradient caused an −6-fold increase in the release of noradrenaline or adrenaline, whereas K⁺ depolarization induced a 12-fold increase in noradrenaline release but only a 9-fold increase in adrenaline release. The ratio of noradrenaline to adrenaline release was 1.24 ± 0.23 upon reversal of the Na⁺/Ca²⁺ exchange, whereas it was 1.83 ± 0.19 for K⁺ depolarization. Reversal of the Na⁺/Ca²⁺ exchange appeared to be as efficient as membrane depolarization in inducing adrenaline release, in that the relation of [Ca²⁺]_c to adrenaline release was the same in both cases. In contrast, we found that for the same average [Ca²⁺]_c, the Ca²⁺ influx through voltage-gated channels was much more efficient than the Ca²⁺ entering through the Na⁺/Ca²⁺ exchanger in inducing noradrenaline release from chromaffin ceils. This greater effectiveness of membrane depolarization in stimulating noradrenaline release suggests that there is a pool of noradrenaline vesicles which is more accessible to Ca²⁺ entering through voltage-gated Ca²⁺ channels than to Ca²⁺ entering through the Na⁺/Ca²⁺ exchanger, whereas the adrenaline vesicles do not distinguish between the source of Ca²⁺.     

Effects of various cations on the slow K conductance increases induced by carbachol, histamine and dopamine inAplysia neurones

A study was made of the effects of various cations other than K⁺ on three K⁺ conductance increases induced by carbachol, histamine and dopamine in an identified group ofAplysia neurones: the ‘A’ neurones of the cerebral ganglion. The 3 responses were sensitive to alterations of both the extracellular and the intracellular concentrations of Na⁺ and Ca²⁺. In particular, they could be reduced markedly by: (a) lowering [Na]₀ (replacing NaCl by either Tris-HCl, glucosamine chloride, MgCl₂ or sucrose); (b) increasing [Na]_i (by intracellular injection of Na⁺, or by blockade of the Na⁺-K⁺ pump); (c) increasing the extracellular divalent cation concentration; or (d) increasing [Ca]_i⁴.Some of the effects of Na⁺ and divalent cations appear to occur on reaction steps common to the three K⁺ responses, while others probably imply reaction steps specific to one of the systems, since they differ according to the agonist used. The sensitivity to Na⁺ and Ca²⁺ of slow inhibitory responses due entirely to an increase in K⁺ conductance must be taken into account in the interpretation of some slow hyperpolarizing responses previously assumed to involve changes in Na⁺ conductance.     

Aquaporin‐4 regulates the velocity and frequency of cortical spreading depression in mice

The astrocyte water channel aquaporin‐4 (AQP4) regulates extracellular space (ECS) K⁺ concentration ([K⁺]_e) and volume dynamics following neuronal activation. Here, we investigated how AQP4‐mediated changes in [K⁺]_e and ECS volume affect the velocity, frequency, and amplitude of cortical spreading depression (CSD) depolarizations produced by surface KCl application in wild‐type (AQP4^+/+) and AQP4‐deficient (AQP4^?/?) mice. In contrast to initial expectations, both the velocity and the frequency of CSD were significantly reduced in AQP4^?/? mice when compared with AQP4^+/+ mice, by 22% and 32%, respectively. Measurement of [K⁺]_e with K⁺‐selective microelectrodes demonstrated an increase to ～35 mM during spreading depolarizations in both AQP4^+/+ and AQP4^?/? mice, but the rates of [K⁺]_e increase (3.5 vs. 1.5 mM/s) and reuptake (t_1/2 33 vs. 61 s) were significantly reduced in AQP4^?/? mice. ECS volume fraction measured by tetramethylammonium iontophoresis was greatly reduced during depolarizations from 0.18 to 0.053 in AQP4^+/+ mice, and 0.23 to 0.063 in AQP4^?/? mice. Analysis of the experimental data using a mathematical model of CSD propagation suggested that the reduced velocity of CSD depolarizations in AQP4^?/? mice was primarily a consequence of the slowed increase in [K⁺]_e during neuronal depolarization. These results demonstrate that AQP4 effects on [K⁺]_e and ECS volume dynamics accelerate CSD propagation. GLIA 2015;63:1860–1869     

Blood–brain barrier mechanisms involved in brain calcium and potassium homeostasis

This study examined the potential roles of the plasma membrane Ca²⁺-ATPase (PMCA) at the blood–CSF and blood–brain barriers in brain Ca²⁺ homeostasis and blood–brain barrier Na⁺/K⁺-ATPase subunits in brain K⁺ homeostasis. During dietary-induced hypo- and hypercalcemia (0.59±0.06 and 1.58±0.12 mM [Ca²⁺]) there was no significant change in choroid plexus PMCA (Western Blots) compared to normocalcemic rats (plasma [Ca²⁺]: 1.06±0.11 mM). In contrast, PMCA in cerebral microvessels isolated from hypocalcemic rats was 150% greater than that in controls (p<0.001). Comparison of the α3 subunit of Na⁺/K⁺-ATPase from cerebral microvessels isolated from hypo-, normo- and hyperkalemic rats (2.3±0.1, 3.9±0.1 and 7.2±0.6 mM [K⁺]) showed a 75% reduction in the amount of this isoform during hyperkalemia. None of the other Na⁺/K⁺-ATPase isoforms varied with plasma [K⁺]. These results suggest that both PMCA and the α3 subunit of Na⁺/K⁺-ATPase at the blood–brain barrier play a role in maintaining a constant brain microenvironment during fluctuations in plasma composition.     

Voltage‐gated sodium channel Nav1.5 contributes to astrogliosis in an in vitro model of glial injury via reverse Na+/Ca2+ exchange

Astrogliosis is a prominent feature of many, if not all, pathologies of the brain and spinal cord, yet a detailed understanding of the underlying molecular pathways involved in the transformation from quiescent to reactive astrocyte remains elusive. We investigated the contribution of voltage‐gated sodium channels to astrogliosis in an in vitro model of mechanical injury to astrocytes. Previous studies have shown that a scratch injury to astrocytes invokes dual mechanisms of migration and proliferation in these cells. Our results demonstrate that wound closure after mechanical injury, involving both migration and proliferation, is attenuated by pharmacological treatment with tetrodotoxin (TTX) and KB‐R7943, at a dose that blocks reverse mode of the Na⁺/Ca²⁺ exchanger (NCX), and by knockdown of Na_v1.5 mRNA. We also show that astrocytes display a robust [Ca²⁺]_i transient after mechanical injury and demonstrate that this [Ca²⁺]_i response is also attenuated by TTX, KB‐R7943, and Na_v1.5 mRNA knockdown. Our results suggest that Na_v1.5 and NCX are potential targets for modulation of astrogliosis after injury via their effect on [Ca²⁺]_i. GLIA 2014;62:1162–1175     

Molecular targets for antiepileptic drug development

This review considers how recent advances in the physiology of ion channels and other potential molecular targets, in conjunction with new information on the genetics of idiopathic epilepsies, can be applied to the search for improved antiepileptic drugs (AEDs). Marketed AEDs predominantly target voltage-gated cation channels (the α subunits of voltage-gated Na⁺ channels and also T-type voltage-gated Ca²⁺ channels) or influence GABA-mediated inhibition. Recently, α2-δ voltage-gated Ca²⁺ channel subunits and the SV2A synaptic vesicle protein have been recognized as likely targets. Genetic studies of familial idiopathic epilepsies have identified numerous genes associated with diverse epilepsy syndromes, including genes encoding Na⁺ channels and GABA_A receptors, which are known AED targets. A strategy based on genes associated with epilepsy in animal models and humans suggests other potential AED targets, including various voltage-gated Ca²⁺ channel subunits and auxiliary proteins, A- or M-type voltage-gated K⁺ channels, and ionotropic glutamate receptors. Recent progress in ion channel research brought about by molecular cloning of the channel subunit proteins and studies in epilepsy models suggest additional targets, including G-protein-coupled receptors, such as GABA_B and metabotropic glutamate receptors; hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel subunits, responsible for hyperpolarization-activated currentI _h; connexins, which make up gap junctions; and neurotransmitter transporters, particularly plasma membrane and vesicular transporters for GABA and glutamate. New information from the structural characterization of ion channels, along with better understanding of ion channel function, may allow for more selective targeting. For example, Na⁺ channels underlying persistent Na⁺ currents or GABA_A receptor isoforms responsible for tonic (extrasynaptic) currents represent attractive targets. The growing understanding of the pathophysiology of epilepsy and the structural and functional characterization of the molecular targets provide many opportunities to create improved epilepsy therapies.