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October, 2006
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Potassium Channels: Cell membrane glycoproteins that are selectively permeable to potassium ions. At least eight major groups of K channels exist and they are made up of dozens of different subunits.

Ion Channels

JoVE 10722

Ion channels maintain the membrane potential of a cell. For most cells, especially excitable ones, the inside has a more negative charge than the outside of the cell, due to a greater number of negative ions than positive ions. For excitable cells, like firing neurons, contracting muscle cells, or sensory touch cells, the membrane potential must be able to change rapidly moving from a negative membrane potential to one that is more positive. To achieve this, cells rely on two types of ion channels: ligand-gated and voltage-gated. Ligand-gated ion channels, also called ionotropic receptors, are transmembrane proteins that form a channel but which also have a binding site. When a ligand binds to the surface, it opens the ion channel. Common ionotropic receptors include the NMDA, kainite, and AMPA glutamate receptors and the nicotinic acetylcholine receptors. When a ligand, like glutamate or acetylcholine, binds to its receptor it allows the influx of sodium (Na+) and calcium (Ca++) ions into the cells. The positive ions, or cations, follow down their electrochemical gradient, moving from the more positive extracellular surface to the less positive (more negative) intracellular surface. This changes the membrane potential near the receptor, which can then activate nearby voltage gated ion channels to propagate the change in membrane potential throughout the cell

 Core: Cell Signaling

Action Potentials

JoVE 10844

Neurons communicate by firing action potentials—the electrochemical signal that is propagated along the axon. The signal results in the release of neurotransmitters at axon terminals, thereby transmitting information in the nervous system. An action potential is a specific “all-or-none” change in membrane potential that results in a rapid spike in voltage.

Neurons typically have a resting membrane potential of about -70 millivolts (mV). When they receive signals—for instance, from neurotransmitters or sensory stimuli—their membrane potential can hyperpolarize (become more negative) or depolarize (become more positive), depending on the nature of the stimulus. If the membrane becomes depolarized to a specific threshold potential, voltage-gated sodium (Na+) channels open in response. Na+ has a higher concentration outside of the cell as compared to the inside, so it rushes in when the channels open, moving down its electrochemical gradient. As positive charge flows in, the membrane potential becomes even more depolarized, in turn opening more channels. As a result, the membrane potential quickly rises to a peak of around +40 mV. At the peak of the action potential, several factors drive the potential back down. The influx of Na+ slows because the Na+ channels start to inactiv

 Core: Nervous System

The Resting Membrane Potential

JoVE 10845

The relative difference in electrical charge, or voltage, between the inside and the outside of a cell membrane, is called the membrane potential. It is generated by differences in permeability of the membrane to various ions and the concentrations of these ions across the membrane.

The membrane potential of a cell can be measured by inserting a microelectrode into a cell and comparing the charge to a reference electrode in the extracellular fluid. The membrane potential of a neuron at rest—that is, a neuron not currently receiving or sending messages—is negative, typically around -70 millivolts (mV). This is called the resting membrane potential. The negative value indicates that the inside of the membrane is relatively more negative than the outside—it is polarized. The resting potential results from two major factors: selective permeability of the membrane, and differences in ion concentration inside the cell compared to outside. Cell membranes are selectively permeable because most ions and molecules cannot cross the lipid bilayer without help, often from ion channel proteins that span the membrane. This is because the charged ions cannot diffuse through the uncharged hydrophobic interior of membranes. The most common intra- and extracellular ions found in the nervous tissue are potassium (K+), sodium (Na+…

 Core: Nervous System

Reconstitution of a Transmembrane Protein, the Voltage-gated Ion Channel, KvAP, into Giant Unilamellar Vesicles for Microscopy and Patch Clamp Studies

1Institut Curie, Centre de Recherche, CNRS, UMR 168, PhysicoChimie Curie, Université Pierre et Marie Curie, 2Kavli Institute for Brain and Mind, University of California, San Diego, 3Molecular Physiology and Biophysics Section, National Institute for Neurological Disorders and Stroke, National Institute of Health

JoVE 52281


Contractility Measurements of Human Uterine Smooth Muscle to Aid Drug Development

1Harris-Wellbeing Preterm Birth Research Centre, Department of Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, 2School of Biomedical Sciences, The University of Queensland, 3Faculty of Chemistry, Institute of Biological Chemistry, University of Vienna, 4Institute for Molecular Bioscience, University of Queensland, 5Center for Physiology and Pharmacology, Medical University of Vienna

JoVE 56639


Isolation of Retinal Arterioles for Ex Vivo Cell Physiology Studies

1Centre for Experimental Medicine, Queen's University of Belfast, 2Centre for Biomedical Sciences (Education), Queen's University of Belfast, 3Department of Pharmaceutical Chemistry and Pharmacognosy, Naresuan University, 4School of Medicine, Dentistry and Biomedical Sciences, Queen's University of Belfast

JoVE 57944


Whole-cell Patch-clamp Recordings of Isolated Primary Epithelial Cells from the Epididymis

1School of Life Science and Technology, ShanghaiTech University, 2Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 3University of Chinese Academy of Sciences, 4Shanghai Institute for Advanced Immunochemical Studies, ShanghaiTech University

JoVE 55700

 Developmental Biology

Recording Brain Electromagnetic Activity During the Administration of the Gaseous Anesthetic Agents Xenon and Nitrous Oxide in Healthy Volunteers

1Centre for Human Psychopharmacology, Swinburne University of Technology, 2Department of Anaesthesia and Pain Management, St. Vincent's Hospital Melbourne, 3Brain and Psychological Science Research Centre, Swinburne University of Technology, 4Department of Anaesthesiology, University of Auckland

JoVE 56881


Flow Cytometric Detection of Newly-formed Breast Cancer Stem Cell-like Cells After Apoptosis Reversal

1School of Life Sciences, The Chinese University of Hong Kong, 2State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, 3Key Laboratory for Regenerative Medicine, Ministry of Education, The Chinese University of Hong Kong, 4Centre for Novel Biomaterials, The Chinese University of Hong Kong

JoVE 58642

 Cancer Research
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