Chloride Channel / Ion Channels / Integral Membrane Proteins .pdf

Chloride Channel / Ion Channels / Integral Membrane Proteins .pdf

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  selfexplanatory.2022 Hello HI नमस्ते ْ‫م‬ُ‫ك‬ْ‫ي‬‫ا‬‫ل‬‫ا‬‫ع‬ ُ‫م‬ ‫ا‬ ‫َل‬َّ ‫الس‬ ِ َّ ‫ٱَّلل‬ ُ‫اة‬‫م‬ْ‫ح‬‫ا‬‫ر‬‫ا‬‫و‬ ُ‫ه‬ُ‫ت‬‫كا‬‫ا‬‫ر‬‫ا‬‫ب‬‫ا‬‫و‬ Saba Parvin Haque M.Sc. Life Sciences (Specialization in Neurobiology) from “Sophia College” (Autonomous), Mumbai.
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  Chloride Channels
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   Ion channelsare integral membrane proteins that form ion- selective, water-filled pores across cellular membranes.  Chloride channels are a subset of ion channels that are selectively permeable to chloride and often to other small monovalent anions.  Chloride channels are found in the plasma membranes of most cells and in the membranes of various intracellular organelles including the endoplasmic reticulum, Golgi apparatus, endosomes and sarcoplasmic reticulum.  The physiological functions of chloride channels include stabilization of resting membrane potentials in muscle and nerve cells, transepithelial transport, cell volume regulation, signal transduction and acidification of intracellular organelles. Introduction
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   Three structuralfamilies of chloride channels have been identified to date. These include the ClC channel family, the cystic fibrosis transmembrane conductance regulator (CFTR) and the g- aminobutyric acid (GABA)-gated and glycine- gated neurotransmitter receptors.  Functional data suggest that additional structural classes of chloride channels exist, but the genes encoding these channels have not yet been identified.  Genetic defects in chloride channels and abnormal regulation of gating cause a variety of human diseases. Introduction
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  What Chloride Channels Do for a Cell?  The effect of opening a chloride channel depends on the driving force for chloride movement across the cell membrane.  The driving force is determined by the algebraic sum of the transmembrane concentration gradient for chloride and the transmembrane electrical potential.  The driving force is called the chloride electro- chemical potential.  When a chloride channel opens, chloride ions may either enter or leave the cell depending on the direction of the chloride electrochemical gradient.
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  What Chloride Channels Do for a Cell?  For plasma membrane chloride channels the concentration gradient is determined by the difference in the chloride concentration in the extracellular and intracellular fluid.  Chloride is the major negatively charged ion in the extracellular fluid.  In mammals the extracellular fluid chloride concentration is about 100 mmol L -1  The concentration of chloride inside cells is variable and depends on the types of chloride transport proteins present in the plasma membrane. If ion-coupled chloride transporters, such as the Na + /Cl - or Na +/K +/2CK - cotransporters, are present in the plasma membrane, the intracellular chloride concentration tends to be high( ~20 mmol L -1)
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   In cellslacking these transporters, the chloride concentration is lower, about 5 mmol L -1  The resting transmembrane electrical potential is always negative inside cells, but in the magnitude of the potential may range from - 30 mV to - 90 mV.  Thus, the concentration gradient always favours chloride movement into cells but the resting electrical potential always favours chloride movement out of cells.  The balance between the two forces will determine the direction of chloride movement.  If the chloride concentration is high inside the cell, the concentration gradient for chloride will be small and the effect of the electrical potential is likely to predominate.  In this case, chloride will move out of the cell, depolarizing the cell membrane, i.e. reducing the inside negative electrical potential.  On the other hand, if the chloride concentration inside the cell is small, there will be a large concentration gradient and it will probably overwhelm the electrical potential, resulting in chloride movement into cells, thereby hyperpolarizing the cell membrane, i.e. increasing the magnitude of the negative membrane potential. What Chloride Channels Do for a Cell ?
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  References  Book: BruceAlberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter, Molecular biology of the cell, 5th Edition.  Akabas, Myles. (2005). Chloride Channels. 10.1038/npg.els.0004061.
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