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Channelopathies

Posted on November 1, 2019 at 12:55 AM


June-Bum Kim, MD, PhD


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Abstract

Channelopathies are a heterogeneous group of disorders resulting from the dysfunction of ion channels located in the membranes of all cells and many cellular organelles. These include diseases of the nervous system (e.g., generalized epilepsy with febrile seizures plus, familial hemiplegic migraine, episodic ataxia, and hyperkalemic and hypokalemic periodic paralysis), the cardiovascular system (e.g., long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia), the respiratory system (e.g., cystic fibrosis), the endocrine system (e.g., neonatal diabetes mellitus, familial hyperinsulinemic hypoglycemia, thyrotoxic hypokalemic periodic paralysis, and familial hyperaldosteronism), the urinary system (e.g., Bartter syndrome, nephrogenic diabetes insipidus, autosomal-dominant polycystic kidney disease, and hypomagnesemia with secondary hypocalcemia), and the immune system (e.g., myasthenia gravis, neuromyelitis optica, Isaac syndrome, and anti-NMDA [N-methyl-D-aspartate] receptor encephalitis). The field of channelopathies is expanding rapidly, as is the utility of molecular-genetic and electrophysiological studies. This review provides a brief overview and update of channelopathies, with a focus on recent advances in the pathophysiological mechanisms that may help clinicians better understand, diagnose, and develop treatments for these diseases.


Keywords: Channelopathies, Ion channels, Genetics, Pathophysiology

Introduction

Channelopathies are diseases that develop because of defects in ion channels caused by either genetic or acquired factors (Fig. 1). Mutations in genes encoding ion channels, which impair channel function, are the most common cause of channelopathies. Consistent with the distribution of ion channels throughout the human body, ion channel defects have been implicated in a wide variety of diseases, including epilepsy, migraine, blindness, deafness, diabetes, hypertension, cardiac arrhythmia, asthma, irritable bowel syndrome, and cancer1-3).



There are remarkable causal heterogeneity (especially genetic) and phenotypic variability in channelopathies, which make the diseases challenging to classify. This review will categorize channelopathies based on the organ system with which they are predominantly associated in both clinical and pathophysiological respects. Nomenclature of genetic diseases described in this article can be found at the Online Mendelian Inheritance in Man (OMIM) website: http://www.ncbi.nlm.nih.gov/omim.


Ion channels

Ion channels are transmembrane proteins that allow the passive flow of ions, both in and out of cells or cellular organelles, following their electrochemical gradients. Because the flux of ions across a membrane results in electrical currents, ion channels play a key role in generating membrane potential and function in diverse cellular activities, such as signal transduction, neurotransmitter release, muscle contraction, hormone secretion, volume regulation, growth, motility, and apoptosis. Ion channels can be classified according to the types of ions passing through them, the factors of their gating, their tissue expression patterns, and their structural characteristics. Ion channels typically exist in one of the three states: open, inactivated closed (refractory period), and resting closed (Fig. 2). The gating (opening and closing) of ion channels is controlled by diverse factors, such as membrane potential (voltage), ligands (e.g., hormones and neurotransmitters), second messengers (e.g., calcium and cyclic nucleotides), light, temperature, and mechanical changes....... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3935107/

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