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PubMed2002

Cardiac channelopathies.

Genetic alterations of various ion channels produce heritable cardiac arrhythmias that predispose affected individuals to sudden death. The investigation of such 'channelopathies' continues to yield remarkable insights into the molecular basis of cardiac excitability. The concept of channelopathies is not restricted to genetic disorders; notably, changes in the expression or post-translational modification of ion channels underlie the fatal arrhythmias associated with heart failure. Recognizing the fundamental defects in channelopathies provides the basis for new strategies of treatment, including tailored pharmacotherapy and gene therapy.

Animals↗

PubMed2000

Channelopathies: potassium-related periodic paralyses and similar disorders.

Channelopathy is a term used to describe clinical problems caused by disorders of membrane ion channels. Included in this disease category are certain types of periodic paralyses, ataxia, myotonia, migraine headache, epilepsy, nephrolithiasis, and long QT syndrome. This article briefly summarizes membrane ion channel structure and function and details several relatively common channelopathies. In hyperkalemic periodic paralysis, mutant skeletal muscle sodium channels fail to close completely after an action potential. This evokes two apparently opposite symptoms: myotonia (caused by a small depolarization and repetitive excitation) or paralysis (caused by larger depolarization and inexcitability). In hypokalemic periodic paralysis, mutation affects the closing of skeletal muscle calcium channels, causing transient paresis or paralysis. The task of the advanced practice nurse is to recognize these disorders, institute appropriate prophylactic measures and treatments, monitor symptom progression, and avoid complications. Understanding of channelopathies is advancing rapidly. On the horizon are therapies tailored to counter specific membrane ion channel defects.

Humans↗

PubMed2004

Activators of cation channels: potential in treatment of channelopathies.

Cation channels are membrane proteins that provide controlled pathways for ion passage through cellular membranes. They play important roles in physiological processes such as secretory transduction, control of ion homeostasis, cell volume, vesicle cycling, and electrical control of excitable tissues. In a variety of channelopathies, ion channel function is reduced, and activators of cation channels are promising candidates to regain channel function in acquired or inherited channelopathies. Shortage in cation channel activators prevents testing of efficiency of activators in a variety of indications. This shortage might result from the relative incapability of modern drug screening methods, but increasing knowledge about cation channel activator binding and action might enable us in the future to use in silico-guided drug design of channel modulators. New compounds such as the HERG channel activator (3R,4R)-4-[3-(6-methoxy-quinolin-4-yl)-3-oxo-propyl]-1-[3-(2,3,5-trifluoro-phenyl)-prop-2-ynyl]-piperidine-3-carboxylic acid (RPR260243) will enable us to increase our understanding in cation channel modulation and to test the concept of channel activation as a clinically relevant principle in treatment of channelopathies.

Cation Transport Proteins↗

PubMed2004

Acquired dendritic channelopathy in temporal lobe epilepsy.

Inherited channelopathies are at the origin of many neurological disorders. Here we report a form of channelopathy that is acquired in experimental temporal lobe epilepsy (TLE), the most common form of epilepsy in adults. The excitability of CA1 pyramidal neuron dendrites was increased in TLE because of decreased availability of A-type potassium ion channels due to transcriptional (loss of channels) and posttranslational (increased channel phosphorylation by extracellular signal-regulated kinase) mechanisms. Kinase inhibition partly reversed dendritic excitability to control levels. Such acquired channelopathy is likely to amplify neuronal activity and may contribute to the initiation and/or propagation of seizures in TLE.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMedDate not supplied

[Epileptic channelopathies].

OBJECTIVE: At the present time the study of epileptogenesis is becoming increasingly interested in the function of ionic channels in which localization of new gene sites and mutations have been aetiopathogenically related to certain syndromes involving epilepsy. The pathology of these channels known as channelopathies is responsible for a certain number of conditions affecting the central nervous and neuromuscular systems. Its clinical expression is often paroxystic. The mutations cause inactivation of the channel, which depending on the degree, conditions the phenotype of the process. DEVELOPMENT: We studied the main epileptic channelopathies related to idiopathic epilepsy syndromes. To date it has been possible to codify four genes responsible for: benign familial neonatal convulsions, generalized epilepsy with febrile convulsions plus and frontal lobe nocturnal dominant autosomal epilepsy, together with other syndromes in which potentially related mutations have arisen. CONCLUSIONS: Ionic channels, both voltage and receptor dependent, are involved in the genesis of idiopathic epilepsy syndromes. Their importance is due to the contribution made to understanding epileptogenesis and the application of this in the investigation of drugs which act by modifying the initial cause of the seizure. Today it may be said that the idiopathic epilepsies, or at least some of them, make up a family of channelopathies.

Chromosomes, Human, Pair 1↗

PubMedDate not supplied

[Neuromuscular hereditary channelopathies: non-dystrophic myotonias, paramyotonias and periodic paralysis].

INTRODUCTION: The ionic channels are complex glycoprotein structures, which cross the lipidic cellular membrane and allow the passage of electrically charged ions from one side of it to the other, thanks to the electrochemical gradient. A channelopathy is a disorder due to anomalous function of the ionic channels. DEVELOPMENT: In this study we analyze particularly the hereditary channelopathies with neuromuscular involvement non dystrophic myotonia, paramyotonias and periodic paralysis, and classify the clinical, physiopathological, molecular, genetic and therapeutic aspects. As far as possible we have divided the different conditions according to the channel involved, due to mutations which affect the sodium, calcium, chloride and potassium channels. We have also included neuromyotonic phenomena which are probably caused by channelopathies. CONCLUSIONS: Probably it will not be long before many of the conditions considered in this article have a better physiopathological explanation, more specific diagnostic procedures and a more rational approach to treatment.

DNA Mutational Analysis↗

PubMed1998

[Physiopathology of calcium channels: identification of calcium channelopathies].

Since a few years, many mutations in genes encoding voltage-dependent ion channels have been identified. The related disorders are quoted as "channelopathies". These mutations are responsible for several skeletal muscle, brain, heart or kidney diseases. Abnormal calcium channels genes are responsible for hypokaleamic periodic paralysis (CACNA1S) as well as some forms of ataxia, cerebellar degeneration and migraine (CACNA1A). The preliminary studies of the recently discovered calcium channelopathies are undergoing. Both in vitro and in vivo studies of the diseased genes should help to the understanding of the related pathologies as well as to extend our knowledge of calcium channel function. In addition, autoantibodies against calcium channels are retrieved in some autoimmune diseases, such as Lambert-Eaton myasthenic syndrome (LEMS). Complementary studies are necessary to identify the precise implication of calcium channels in these auto-immune channelopathies.

Brain Diseases↗

PubMed2006

Molecular basis of inherited calcium channelopathies: role of mutations in pore-forming subunits.

The pore-forming alpha subunits of voltage-gated calcium channels contain the essential biophysical machinery that underlies calcium influx in response to cell depolarization. In combination with requisite auxiliary subunits, these pore subunits form calcium channel complexes that are pivotal to the physiology and pharmacology of diverse cells ranging from sperm to neurons. Not surprisingly, mutations in the pore subunits generate diverse pathologies, termed channelopathies, that range from failures in excitation-contraction coupling to night blindness. Over the last decade, major insights into the mechanisms of pathogenesis have been derived from animals showing spontaneous or induced mutations. In parallel, there has been considerable growth in our understanding of the workings of voltage-gated ion channels from a structure-function, regulation and cell biology perspective. Here we document our current understanding of the mutations underlying channelopathies involving the voltage-gated calcium channel alpha subunits in humans and other species.

Animals↗

PubMed2006

Calcium channelopathies.

Intracellular calcium ([Ca2+]i) is highly regulated in eukaryotic cells. The free [Ca2+]i is approximately four orders of magnitude less than that in the extracellular environment. It is, therefore, an electrochemical gradient favoring Ca2+ entry, and transient cellular activation increasing Ca2+ permeability will lead to a transient increase in [Ca2+]i. These transient rises of [Ca2+]i trigger or regulate diverse intracellular events, including metabolic processes, muscle contraction, secretion of hormones and neurotransmitters, cell differentiation, and gene expression. Hence, changes in [Ca2+]i act as a second messenger system coordinating modifications in the external environment with intracellular processes. Notably, information on the molecular genetics of the membrane channels responsible for the influx of Ca2+ ions has led to the discovery that mutations in these proteins are linked to human disease. Ca2+ channel dysfunction is now known to be the basis for several neurological and muscle disorders such as migraine, ataxia, and periodic paralysis. In contrast to other types of genetic diseases, Ca2+ channelopathies can be studied with precision by electrophysiological methods, and in some cases, the results have been highly rewarding with a biophysical phenotype that correlates with the ultimate clinical phenotype. This review outlines recent advances in genetic, molecular, and pathophysiological aspects of human Ca2+ channelopathies.

Animals↗

PubMed2002

Isaacs' syndrome as a potassium channelopathy of the nerve.

Isaacs' syndrome (acquired neuromyotonia) is an antibody-mediated potassium channel disorder (channelopathy). The target channel proteins of the antigens are voltage-gated potassium channels (VGKCs), especially dendrotoxin-sensitive fast potassium channels. The suppression of voltage-gated outward K(+) current by antibodies induces hyperexcitability of the peripheral nerve. Patch clamp studies show that antibodies may not directly block the kinetics of VGKCs but may decrease channel density. Electrophysiological, pharmacological, and immunological findings indicate that the site of origin of spontaneous discharges is principally in the distal portion of the motor nerve and/or within the terminal arborization. The spectrum of potassium channelopathies is expanding. The existence of antibodies against VGKCs should be considered in patients who present with generalized nerve hyperexcitability of undetermined etiology.

Humans↗

PubMed2006

A new paradigm of channelopathy in epilepsy syndromes: intracellular trafficking abnormality of channel molecules.

Mutations in genes encoding ion channels in brain neurons have been identified in various epilepsy syndromes. In neuronal networks, "gain-of-function" of channels in excitatory neurotransmission could lead to hyper-excitation while "loss-of-function" in inhibitory transmission impairs neuronal inhibitory system, both of which can result in epilepsy. A working hypothesis to view epilepsy as a disorder of channel or "channelopathy" seems rational to explore the pathogenesis of epilepsy. However, the imbalance resulting from channel dysfunction is not sufficient to delineate the pathogenesis of all epilepsy syndromes of which the underlying channel abnormalities have been verified. Mutations identified in epilepsy, mainly in genes encoding subunits of GABA(A) receptors, undermine intracellular trafficking, thus leading to retention of channel molecules in the endoplasmic reticulum (ER). This process may cause ER stress followed by apoptosis, which is a known pathomechanism of certain neurodegenerative disorders. Thus, the pathomechanism of "channel trafficking abnormality" may provide a new paradigm to channelopathy to unsolved questions underlying epilepsy, such as differences between generalized epilepsy with febrile seizures plus and severe myoclonic epilepsy in infancy, which share the causative genetic abnormalities in the same genes and hence are so far considered to be within the spectrum of one disease entity or allelic variants.

Codon, Nonsense↗

PubMed2005

Depolarization/repolarization, electrocardiographic abnormalities, and arrhythmias in cardiac channelopathies.

Investigation of the etiology and pathogeneses of the genetic cardiac channelopathies has provided important insight into the mechanisms of ventricular arrhythmias. Some of these diseases are rare, such as the short QT-interval syndrome, but others such as the Brugada syndrome are the most common cause of unexplained sudden cardiac death in young men in Southeast Asia and Japan. Knowledge of the specific ion-channel defect causing the disease or syndrome is leading to pharmacological approaches that attempt to correct the ion transfer defects in channelopathies. The most clinically important challenge is to recognize which patients with the Brugada electrocardiogram who do not have a positive family history of this condition and do not have a history of syncope or aborted sudden death are at risk for arrhythmic death.

Arrhythmias, Cardiac↗

PubMed2005

The h-channel: a potential channelopathy in epilepsy?

Ion channelopathy is a proven cause of inherited human epilepsy, and may play a role in acquired epileptic syndromes as well. Of the many ion channel causes of epilepsy, the h-channel is a potential new addition. H-channels are voltage-gated ion channels with unique biophysical properties. The h-channel exerts a significant modulatory influence on neuronal excitability, and is a target of antiepileptic drugs. Further, its activity is influenced by seizures, raising the question of whether it may play a role in epileptogenesis as well. This review summarizes the evidence for the contribution of h-channels to seizures and epilepsy, and outlines hypotheses concerning the existence of an "h-channelopathy" in human epilepsy.

Animals↗

PubMed2004

Electrophysiology and molecular pharmacology of muscle channelopathies.

As voltage-gated ion channels are essential for membrane excitation, it is not surprising that mutations in the respective channel genes cause diseases characterised by altered cell excitability. Skeletal muscle was the first tIssue in which such diseases, namely the myotonias and periodic paralyses, were recognised as ion channelopathies. The detection of the functional defect that is brought about by the disease-causing mutation is essential for the understanding of the pathology. Much progress on the road to this aim was achieved by the combination of molecular biology and electrophysiological patch clamp techniques. The functional expression of the mutations in expression systems allows to study the functional alterations of mutant channels and to develop new strategies for the therapy of ion channelopathies, e.g. by designing drugs that specifically suppress the effects of malfunctioning channels.

Electrophysiology↗

PubMed2005

[Electrophysiological signs of muscle channelopathies by causal mutation].

Nondystrophic myotonias and familial periodic paralyses are disorders of muscle excitability caused by mutations in genes coding for voltage-gated ion channels. Electromyographic (EMG) diagnosis of these diseases is based on needle searching of myotonic discharges and on several exercise tests, performed by surface recording of compound muscle action potential (CMAP) before and after voluntary contractions of various durations. After a short exercise test (10 seconds contraction), three abnormal changes of CMAP have been defined in muscle channelopathies: 1) appearance of repetitive discharges (post-exercise myotonic potentials, PEMP), 2) transient or long-lasting amplitude reduction, 3) long-lasting amplitude increase. These abnormalities become more marked or decline with exercise repetition (repeated brief exercise test), depending on the causal mutation. After long exercise test (5 minutes contraction), three other abnormalities of CMAP amplitude have been described: 1) immediate increase, 2) immediate decrease, 3) progressive or delayed decrease. Combining the responses to the different tests has disclosed five main EMG types of muscle channelopathies (I to V), that correlated with different pathophysiological mechanisms and with subgroups of mutations. This classification may guide molecular diagnosis in clinical practice.

Action Potentials↗

PubMedDate not supplied

Spinocerebellar ataxia type 6: channelopathy or glutamine repeat disorder?

Spinocerebellar ataxia type 6 (SCA6) is due to small expansions of a CAG repeat at the 3' end of the CACNA1A gene, coding for the alpha(1A) subunit of voltage-gated calcium channels type P/Q, expressed in the cerebellar Purkinje and granule cells. It is one of three allelic disorders, the other two being episodic ataxia type 2 (EA2), due mostly to protein truncating mutations, and familial hemiplegic migraine, associated with missense mutations. The latter disorders, due to point mutations altering the P/Q channel activity, clearly belong to the group of channelopathies. For SCA6, due to CAGn expansions, a toxic gain of function might, instead, be envisaged homologous to that of glutamine repeat disorders. A comparison between SCA6 and EA2 phenotypes performed on available literature data, shows that the clinical features of the two disorders are widely overlapping and that the differences could be accounted for with the older age of patients in the SCA6 group. A similar phenotype in the two disorders could imply the same pathogenic process. Functional analyses on cells expressing the protein with an expanded polyglutamine stretch have shown, in fact, an altered channel activity. In conclusion, available data seem to suggest that SCA6 is more likely belonging to channelopathies than to polyglutamine disorders.

Calcium Channels↗

PubMed2003

Channelopathies in pediatric neurology.

Although the genetic neurologic channelopathies are uncommon, they serve as models that further understanding of disease mechanisms in paroxysmal disorders. Many other neurologic channelopathies likely will be identified in the future.

Child↗

PubMed2002

[Andersen syndrome, ventricular arrhythmias and channelopathy (a case report)].

INTRODUCTION: Recent advances in molecular genetic research have provided new insights into severe ventricular arrhythmias related to channelopathies. CASE REPORT: A case of Andersen's syndrome followed during fourteen years is reported. This rare familial periodic paralysis is characterized by its association with dysmorphic features (micrognatia) and ventricular arrhythmias. COMMENTS: Andersen's syndrome has been attributed to a mutation in the KCNJ2 gene which is involved not only in stabilizing cardiac rhythm, but also in modulating the excitability of skeletal muscle and in morphogenesis. This disease must be distinguished from hyperkalemic periodic paralysis due to a mutation in the skeletal muscle sodium channel gene (SCN4A) and from hypokalemic periodic paralysis related to dihydropyridine receptor mutation (CACNL1A3). Furthermore, it may not be confused with others rhythmic channelopathies (long QT syndromes, catecholaminergic polymorphic ventricular tachycardia and Brugada's syndrome).

Adolescent↗