51
|
Marini C, Mantegazza M. Na+ channelopathies and epilepsy: recent advances and new perspectives. Expert Rev Clin Pharmacol 2012; 3:371-84. [PMID: 22111617 DOI: 10.1586/ecp.10.20] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mutations of ion channel genes have a major role in the pathogenesis of several epilepsies, confirming that some epilepsies are disorders due to the impairment of ion channel function (channelopathies). Voltage-gated Na(+) channels (VGSCs) play an essential role in neuronal excitability; it is, therefore, not surprising that most mutations associated with epilepsy have been identified in genes coding for VGSCs subunits. Epilepsies linked to VGSCs mutations range in severity from mild disorders, such as benign neonatal-infantile familial seizures and febrile seizures, to severe and drug-resistant epileptic encephalopathies. SCN1A is the most clinically relevant of all of the known epilepsy genes, several hundred mutations have been identified in this gene. This review will summarize recent advances and new perspectives on Na(+) channels and epilepsy. A better understanding of the genetic basis and of how gene defects cause seizures is mandatory to direct future research for newer selective and more efficacious treatments.
Collapse
Affiliation(s)
- Carla Marini
- Child Neurology Unit, Pediatric Hospital A. Meyer, University of Firenze, Viale Pieraccini, Florence, Italy.
| | | |
Collapse
|
52
|
Fu LY, Cummins TR, Moczydlowski EG. Sensitivity of cloned muscle, heart and neuronal voltage-gated sodium channels to block by polyamines: a possible basis for modulation of excitability in vivo. Channels (Austin) 2012; 6:41-9. [PMID: 22522923 DOI: 10.4161/chan.19001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Spermidine and spermine, are endogenous polyamines (PAs) that regulate cell growth and modulate the activity of numerous ion channel proteins. In particular, intracellular PAs are potent blockers of many different cation channels and are responsible for strong suppression of outward K (+) current, a phenomenon known as inward rectification characteristic of a major class of KIR K (+) channels. We previously described block of heterologously expressed voltage-gated Na (+) channels (NaV) of rat muscle by intracellular PAs and PAs have recently been found to modulate excitability of brain neocortical neurons by blocking neuronal NaV channels. In this study, we compared the sensitivity of four different cloned mammalian NaV isoforms to PAs to investigate whether PA block is a common feature of NaV channel pharmacology. We find that outward Na (+) current of muscle (NaV 1.4), heart (NaV 1.5), and neuronal (NaV 1.2, NaV 1.7) NaV isoforms is blocked by PAs, suggesting that PA metabolism may be linked to modulation of action potential firing in numerous excitable tissues. Interestingly, the cardiac NaV 1.5 channel is more sensitive to PA block than other isoforms. Our results also indicate that rapid binding of PAs to blocking sites in the NaV 1.4 channel is restricted to access from the cytoplasmic side of the channel, but plasma membrane transport pathways for PA uptake may contribute to long-term NaV channel modulation. PAs may also play a role in drug interactions since spermine attenuates the use-dependent effect of the lidocaine, a typical local anesthetic and anti-arrhythmic drug.
Collapse
Affiliation(s)
- Li-Ying Fu
- Department of Pathology, Yale University School of Medicine, New Haven, CT, USA
| | | | | |
Collapse
|
53
|
Tryba AK, Kaczorowski CC, Ben-Mabrouk F, Elsen FP, Lew SM, Marcuccilli CJ. Rhythmic intrinsic bursting neurons in human neocortex obtained from pediatric patients with epilepsy. Eur J Neurosci 2011; 34:31-44. [PMID: 21722205 DOI: 10.1111/j.1460-9568.2011.07746.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Neocortical oscillations result from synchronized activity of a synaptically coupled network and can be strongly influenced by the intrinsic firing properties of individual neurons. As such, the intrinsic electroresponsive properties of individual neurons may have important implications for overall network function. Rhythmic intrinsic bursting (rIB) neurons are of particular interest, as they are poised to initiate and/or strongly influence network oscillations. Although neocortical rIB neurons have been recognized in multiple species, the current study is the first to identify and characterize rIB neurons in the human neocortex. Using whole-cell current-clamp recordings, rIB neurons (n = 12) are identified in human neocortical tissue resected from pediatric patients with intractable epilepsy. In contrast to human regular spiking neurons (n = 12), human rIB neurons exhibit rhythmic bursts of action potentials at frequencies of 0.1-4 Hz. These bursts persist after blockade of fast excitatory neurotransmission and voltage-gated calcium channels. However, bursting is eliminated by subsequent application of the persistent sodium current (I(NaP)) blocker, riluzole. In the presence of riluzole (either 10 or 20 μm), human rIB neurons no longer burst, but fire tonically like regular spiking neurons. These data demonstrate that I(NaP) plays a critical role in intrinsic oscillatory activity observed in rIB neurons in the human neocortex. It is hypothesized that aberrant changes in I(NaP) expression and/or function may ultimately contribute to neurological diseases that are linked to abnormal network activity, such as epilepsy.
Collapse
Affiliation(s)
- Andrew K Tryba
- Department of Physiology, The Medical College of Wisconsin, Milwaukee, WI 53226, USA.
| | | | | | | | | | | |
Collapse
|
54
|
Pegg AE, Wang X. Mouse models to investigate the function of spermine. Commun Integr Biol 2011; 2:271-4. [PMID: 19641749 DOI: 10.4161/cib.2.3.8225] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2009] [Accepted: 02/17/2009] [Indexed: 11/19/2022] Open
Abstract
Many functions have been ascribed to polyamines, but there has been no clear identification of a unique role for spermine. The Gy mouse has a deletion of part of the X chromosome that includes the SMS gene encoding spermine synthase. Tissues from male Gy mice have no spermine but increased spermidine. They have multiple abnormalities including a tendency to sudden death, small size, circling behavior and other neurological symptoms, sterility and deafness. These changes are reversed by breeding with mice expressing a spermine synthase transgene. Detailed studies of hearing in Gy mice show that the absence of spermine synthase leads to loss of the endocochlear potential. Since this potential requires the cochlear lateral wall-specific Kir4.1 channel, regulation by spermine of transport via these channels appears to be an essential function. A similar spermine-related defect in the functioning of cardiac Kir channels could account for arrhythmias leading to sudden death. The effect of the absence of spermine on glutamate receptor ion channels in the brain may account for the neurological symptoms and could contribute to the lack of fertility and normal growth but more direct effects on gene expression are also possible. Advantages and limitations of the Gy model are discussed.
Collapse
Affiliation(s)
- Anthony E Pegg
- Department of Cellular and Molecular Physiology; Milton S. Hershey Medical Center; Pennsylvania State University College of Medicine; Hershey, PA USA
| | | |
Collapse
|
55
|
Bell MR, Belarde JA, Johnson HF, Aizenman CD. A neuroprotective role for polyamines in a Xenopus tadpole model of epilepsy. Nat Neurosci 2011; 14:505-12. [PMID: 21378970 DOI: 10.1038/nn.2777] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Accepted: 01/24/2011] [Indexed: 11/09/2022]
Abstract
Polyamines are endogenous molecules involved in cell damage following neurological insults, although it is unclear whether polyamines reduce or exacerbate this damage. We used a developmental seizure model in which we exposed Xenopus laevis tadpoles to pentylenetetrazole (PTZ), a known convulsant. We found that, after an initial PTZ exposure, seizure onset times were delayed in response to a second PTZ exposure 4 h later. This protective effect was a result of activity-dependent increases in synthesis of putrescine, the simplest polyamine. Unlike more complex polyamines that directly modulate ion channels, putrescine exerted its effect by altering the balance of excitation to inhibition. Tectal neuron recordings, 4 h after the initial seizure, revealed an elevated frequency of GABAergic spontaneous inhibitory postsynaptic currents. Our data suggest that this effect is mediated by an atypical pathway that converts putrescine into GABA, which then activates presynaptic GABA(B) receptors. Our data suggest that polyamines have a previously unknown neuroprotective role in the developing brain.
Collapse
Affiliation(s)
- Mark R Bell
- Department of Neuroscience, Brown University, Providence, Rhode Island, USA
| | | | | | | |
Collapse
|
56
|
Chen S, Su H, Yue C, Remy S, Royeck M, Sochivko D, Opitz T, Beck H, Yaari Y. An increase in persistent sodium current contributes to intrinsic neuronal bursting after status epilepticus. J Neurophysiol 2010; 105:117-29. [PMID: 20980543 DOI: 10.1152/jn.00184.2010] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Brain damage causes multiple changes in synaptic function and intrinsic properties of surviving neurons, leading to the development of chronic epilepsy. In the widely used pilocarpine-status epilepticus (SE) rat model of temporal lobe epilepsy (TLE), a major alteration is the marked increase in the fraction of intrinsically bursting CA1 pyramidal cells. Here we have differentiated between two types of bursting phenotypes: 1) bursting in response to threshold-straddling excitatory current pulses (low-threshold bursting) and 2) bursting only in response to suprathreshold stimuli (high-threshold bursting). Low-threshold bursting prevailed in 46.5% of SE-experienced neurons sampled 1-4 wk after pilocarpine-SE, but was rarely seen in control neurons (1.9%). As previously shown, it appeared to be driven predominantly by a T-type Ca(2+) current (I(CaT)) in the apical dendrites. After blocking low-threshold bursting with Ni(2+), the same neurons still manifested a high-threshold bursting phenotype. Another 40.1% of SE-experienced neurons displayed only a high-threshold bursting phenotype and the remaining 13.4% of these neurons were nonbursters. Altogether, high-threshold bursting prevailed in 86.6% of SE-experienced neurons, but only in 33.0% of control neurons. Several lines of evidence indicated that high-threshold bursting is driven by persistent Na(+) current (I(NaP)) at or near the soma. Congruently, I(NaP) was 1.5-fold larger in SE-experienced versus control neurons. We conclude that an increase in I(NaP), conjointly with an increase in I(CaT), strongly contributes to the predominance of bursting phenotypes in CA1 pyramidal cells early after pilocarpine-SE and thus likely plays a role in the development of a chronic epileptic condition in this TLE model.
Collapse
Affiliation(s)
- Shmuel Chen
- Department of Medical Neurobiology, Hebrew University-Hadassah School of Medicine, P.O. Box 12272, Jerusalem 91121, Israel
| | | | | | | | | | | | | | | | | |
Collapse
|
57
|
Wu J, Shang Z, Wu J, Jiang X, Moschou PN, Sun W, Roubelakis-Angelakis KA, Zhang S. Spermidine oxidase-derived H₂O₂ regulates pollen plasma membrane hyperpolarization-activated Ca(2+) -permeable channels and pollen tube growth. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2010; 63:1042-53. [PMID: 20626657 DOI: 10.1111/j.1365-313x.2010.04301.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Spermidine (Spd) has been correlated with various physiological and developmental processes in plants, including pollen tube growth. In this work, we show that Spd induces an increase in the cytosolic Ca(2+) concentration that accompanies pollen tube growth. Using the whole-cell patch clamp and outside-out single-channel patch clamp configurations, we show that exogenous Spd induces a hyperpolarization-activated Ca(2+) current: the addition of Spd cannot induce the channel open probability increase in excised outside-out patches, indicating that the effect of Spd in the induction of Ca(2+) currents is exerted via a second messenger. This messenger is hydrogen peroxide (H₂O₂), and is generated during Spd oxidation, a reaction mediated by polyamine oxidase (PAO). These reactive oxygen species trigger the opening of the hyperpolarization-activated Ca(2+) -permeable channels in pollen. To provide further evidence that PAO is in fact responsible for the effect of Spd on the Ca(2+) -permeable channels, two Arabidopsis mutants lacking expression of the peroxisomal-encoding AtPAO3 gene, were isolated and characterized. Pollen from these mutants was unable to induce the opening of the Ca(2+) -permeable channels in the presence of Spd, resulting in reduced pollen tube growth and seed number. However, a high Spd concentration triggers a Ca(2+) influx beyond the optimal, which has a deleterious effect. These findings strongly suggest that the Spd-derived H₂O₂ signals Ca(2+) influx, thereby regulating pollen tube growth.
Collapse
Affiliation(s)
- Juyou Wu
- College of Horticulture, State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing 210095, China
| | | | | | | | | | | | | | | |
Collapse
|
58
|
Carta F, Temperini C, Innocenti A, Scozzafava A, Kaila K, Supuran CT. Polyamines Inhibit Carbonic Anhydrases by Anchoring to the Zinc-Coordinated Water Molecule. J Med Chem 2010; 53:5511-22. [DOI: 10.1021/jm1003667] [Citation(s) in RCA: 183] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Fabrizio Carta
- Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy
| | - Claudia Temperini
- Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy
| | - Alessio Innocenti
- Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy
| | - Andrea Scozzafava
- Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy
| | - Kai Kaila
- Department of Biosciences and Neuroscience Center, University of Helsinki, P.O. Box 65, 000140 Helsinki, Finland
| | - Claudiu T. Supuran
- Università degli Studi di Firenze, Polo Scientifico, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy
| |
Collapse
|
59
|
Mantegazza M, Curia G, Biagini G, Ragsdale DS, Avoli M. Voltage-gated sodium channels as therapeutic targets in epilepsy and other neurological disorders. Lancet Neurol 2010; 9:413-24. [PMID: 20298965 DOI: 10.1016/s1474-4422(10)70059-4] [Citation(s) in RCA: 320] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Voltage-gated sodium channels (VGSCs) are key mediators of intrinsic neuronal and muscle excitability. Abnormal VGSC activity is central to the pathophysiology of epileptic seizures, and many of the most widely used antiepileptic drugs, including phenytoin, carbamazepine, and lamotrigine, are inhibitors of VGSC function. These antiepileptic drugs might also be efficacious in the treatment of other nervous system disorders, such as migraine, multiple sclerosis, neurodegenerative diseases, and neuropathic pain. In this Review, we summarise the structure and function of VGSCs and their involvement in the pathophysiology of several neurological disorders. We also describe the biophysical and molecular bases for the mechanisms of action of antiepileptic VGSC blockers and discuss the efficacy of these drugs in the treatment of epileptic and non-epileptic disorders. Overall, clinical and experimental data indicate that these drugs are efficacious for a range of diseases, and that the development of drugs with enhanced selectivity for specific VGSC isoforms might be an effective and novel approach for the treatment of several neurological diseases.
Collapse
Affiliation(s)
- Massimo Mantegazza
- Dipartimento di Neurofisiopatologia, Fondazione Istituto Neurologico C Besta, Milano, Italy
| | | | | | | | | |
Collapse
|
60
|
Ivanov IP, Firth AE, Atkins JF. Recurrent Emergence of Catalytically Inactive Ornithine Decarboxylase Homologous Forms That Likely Have Regulatory Function. J Mol Evol 2010; 70:289-302. [DOI: 10.1007/s00239-010-9331-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2009] [Accepted: 02/17/2010] [Indexed: 10/19/2022]
|
61
|
Pegg AE, Michael AJ. Spermine synthase. Cell Mol Life Sci 2010; 67:113-21. [PMID: 19859664 PMCID: PMC2822986 DOI: 10.1007/s00018-009-0165-5] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Revised: 08/24/2009] [Accepted: 09/28/2009] [Indexed: 10/20/2022]
Abstract
Spermine is present in many organisms including animals, plants, some fungi, some archaea, and some bacteria. It is synthesized by spermine synthase, a highly specific aminopropyltransferase. This review describes spermine synthase structure, genetics, and function. Structural and biochemical studies reveal that human spermine synthase is an obligate dimer. Each monomer contains a C-terminal domain where the active site is located, a central linking domain that also forms the lid of the catalytic domain, and an N-terminal domain that is structurally very similar to S-adenosylmethionine decarboxylase. Gyro mice, which have an X-chromosomal deletion including the spermine synthase (SMS) gene, lack all spermine and have a greatly reduced size, sterility, deafness, neurological abnormalities, and a tendency to sudden death. Mutations in the human SMS lead to a rise in spermidine and reduction of spermine causing Snyder-Robinson syndrome, an X-linked recessive condition characterized by mental retardation, skeletal defects, hypotonia, and movement disorders.
Collapse
Affiliation(s)
- Anthony E Pegg
- Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
| | | |
Collapse
|
62
|
Abstract
Polyamines are ubiquitous small basic molecules that play multiple essential roles in mammalian physiology. Their cellular content is highly regulated and there is convincing evidence that altered metabolism is involvement in many disease states. Drugs altering polyamine levels may therefore have a variety of important targets. This review will summarize the current state of understanding of polyamine metabolism and function, the regulation of polyamine content, and heritable pathological conditions that may be derived from altered polyamine metabolism.
Collapse
Affiliation(s)
- Anthony E Pegg
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
| |
Collapse
|
63
|
Wu SN, Chen BS, Hsu TI, Peng H, Wu YH, Lo YC. Analytical studies of rapidly inactivating and noninactivating sodium currents in differentiated NG108-15 neuronal cells. J Theor Biol 2009; 259:828-36. [PMID: 19446569 DOI: 10.1016/j.jtbi.2009.05.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2009] [Revised: 04/07/2009] [Accepted: 05/06/2009] [Indexed: 11/16/2022]
Abstract
The rapidly inactivating (I(Naf)) and noninactivating Na(+) currents (I(Na)(()(NI)())) were characterized in NG108-15 neuronal cells differentiated with dibutyryl cyclic AMP in this study. Standard activation and inactivation protocols were used to evaluate the steady-state and kinetic properties of the I(Naf) present in these cells. The voltage protocols with a slowly depolarizing ramp were implemented to examine the properties of I(Na)(()(NI)()). Based on experimental data and computer simulations, a window component of the rapidly inactivating sodium current (I(Naf)(()(W)())) was also generated in response to the slowly depolarizing ramp. The I(Naf)(()(W)()) was subtracted from I(Na)(()(NI)()) to yield the persistent Na(+) current (I(Na)(()(P)())). Our results demonstrate the presence of I(Na)(()(P)()) in these cells. In addition to modifying the steady-state inactivation of I(Naf), ranolazine or riluzloe could be effective in blocking I(Naf)(()(W)()) and I(Na)(()(P)()). The ability of ranolazine and riluzole to suppress I(Na)(()(P)()) was greater than their ability to inhibit I(Naf)(()(W)()). In current-clamp recordings, current-induced voltage oscillations were applied to elicit action potentials (APs) through a gradual transition between spontaneous depolarization and upstroke. Ranolazine or riluzole at a concentration of 3 microM then effectively suppressed the AP firing generated by oscillatory changes in membrane current. The data suggest that a small rise in I(Na)(()(NI)()) facilitates neuronal hyper-excitability due the decreased threshold of AP initiation. The underlying mechanism of the inhibitory actions of ranolazine or riluzole on membrane potential in neurons or neuroendocrine cells in vivo may thus be associated with their blocking of I(Na)(()(NI)()).
Collapse
Affiliation(s)
- Sheng-Nan Wu
- Department of Physiology, National Cheng Kung University Medical College, Tainan 70101, Taiwan.
| | | | | | | | | | | |
Collapse
|