ion channel

(noun)

a protein complex or single protein that penetrates a cell membrane and catalyzes the passage of specific ions through that membrane

Related Terms

Examples of ion channel in the following topics:

  • Ion Channels

    • Ion channels are membrane proteins that allow ions to travel into or out of a cell.
    • Most channels are specific (selective) for one ion.
    • When a channel is open, ions permeate through the channel pore down the transmembrane concentration gradient for that particular ion.
    • Voltage-gated ion channels, also known as voltage dependent ion channels, are channels whose permeability is influenced by the membrane potential.
    • A schematic representation of an ion channel.

  • Nerve Impulse Transmission within a Neuron: Resting Potential

    • To enter or exit the neuron, ions must pass through special proteins called ion channels that span the membrane.
    • Ion channels have different configurations: open, closed, and inactive .
    • Some ion channels need to be activated in order to open and allow ions to pass into or out of the cell.
    • Ion channels that change their structure in response to voltage changes are called voltage-gated ion channels.
    • Voltage-gated ion channels regulate the relative concentrations of different ions inside and outside the cell.

  • Ionotropic and Metabotropic Receptors

    • One of them is ligand-gated ion channels (LGICs) inotropic receptor and the other is metabotropic G- protein coupled receptor.
    • Ionotropic  receptors are a group of transmembrane ion channels that are opened or closed in response to the binding of a chemical messenger (i.e., a ligand) such as a neurotransmitter.The binding site of endogenous ligands on LGICs protein complexes are normally located on a different portion of the protein (an allosteric binding site) from where the ion conduction pore is located.The ion channel is regulated by a ligand and is usually very selective to one or more ions such as Na+, K+, Ca2+, or Cl-.
    • The prototypic ligand-gated ion channel is the nicotinic acetylcholine receptor .
    • With a sufficient number of channels opening at once, the inward flow of positive charges carried by Na+ ions depolarizes the postsynaptic membrane enough to initiate an action potential.
    • Metabotropic receptor is a subtype of membrane receptors that do not form an ion channel pore but use the signal transduction mechanisms often G proteins to activate a series of intracellular events using second messenger chemicals.

  • Membrane Potentials as Signals

    • Ion transporter/pump proteins actively push ions across the membrane to establish concentration gradients across the membrane, and ion channels allow ions to move across the membrane down those concentration gradients, a process known as facilitated diffusion.
    • Signals are generated by opening or closing of ion channels at one point in the membrane, producing a local change in the membrane potential that causes electric current to flow rapidly to other points in the membrane.
    • The opening and closing of ion channels can induce a departure from the resting potential.
    • The changes in membrane potential can be small or larger (graded potentials) depending on how many ion channels are activated and what type they are.
    • Action potentials are generated by the activation of certain voltage-gated ion channels.

  • Nerve Impulse Transmission within a Neuron: Action Potential

    • When neurotransmitter molecules bind to receptors located on a neuron's dendrites, voltage-gated ion channels open.
    • As K+ ions leave the cell, the membrane potential once again becomes negative.
    • Eventually, the extra K+ ions diffuse out of the cell through the potassium leakage channels, bringing the cell from its hyperpolarized state back to its resting membrane potential.
    • The flow of ions through these channels, particularly the Na+ channels, regenerates the action potential over and over again along the axon.
    • At the same time, Na+ channels close. (4) The membrane becomes hyperpolarized as K+ ions continue to leave the cell.

  • Chemiosmosis and Oxidative Phosphorylation

    • Chemiosmosis is the movement of ions across a selectively permeable membrane, down their electrochemical gradient.
    • The uneven distribution of H+ ions across the membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient) owing to the hydrogen ions' positive charge and their aggregation on one side of the membrane.
    • If the membrane were open to diffusion by the hydrogen ions, the ions would tend to spontaneously diffuse back across into the matrix, driven by their electrochemical gradient.
    • However, many ions cannot diffuse through the nonpolar regions of phospholipid membranes without the aid of ion channels.
    • At the end of the pathway, the electrons are used to reduce an oxygen molecule to oxygen ions.

  • Electric Potential in Human

    • Typical ions used to generate resting potential include potassium, chloride, and bicarbonate.
    • Potentials can change as ions move across the cell membrane.
    • This can occur passively, as ions diffuse through ion channels in the membrane.
    • Active transport of ions across a cell membrane is also a possibility.
    • This involves ion pumps using energy to push an ion from an area of lower concentration to one of higher concentration.

  • The Action Potential and Propagation

    • The depolarization, also called the rising phase, is caused when positively charged sodium ions (Na+) suddenly rush through open voltage gated sodium channels into a neuron.
    • The repolarizaton, or falling phase, is caused by the slow closing of sodium channels and the opening of voltage gated potassium channels.
    • As the sodium ion entry declines, the slow voltage gated potassium channels open and potassium ions rush out of the cell.
    • The hyper polarization is a phase where some potassium channels remain open, and sodium channels reset.
    • The period from the opening of the sodium channels until the sodium channels begin to reset is called the absolute refractory period.

  • Facilitated transport

    • Similarly, a gated channel protein often remains closed, not allowing substances into the cell until it receives a signal (like the binding of an ion) to open.
    • However, these materials are ions or polar molecules that are repelled by the hydrophobic parts of the cell membrane.
    • The attachment of a particular ion to the channel protein may control the opening or other mechanisms or substances may be involved.
    • In some tissues, sodium and chloride ions pass freely through open channels, whereas in other tissues, a gate must be opened to allow passage.
    • Glucose, water, salts, ions, and amino acids needed by the body are filtered in one part of the kidney.

  • Gap Junctions

    • Each gap junction channel is made up of two half channels (hemichannels), one in each cell’s membrane. 
    • Each of these half channels is called a connexon. 
    • The molecules that may cross this channel include the likes of ions, regulatory proteins, and metabolites (products of metabolism).  
    • Examples of this includes calcium ions and cAMP (cyclic adenosine monophosphate).  
    • The ability of the channel to open or close is made possibly thanks in part to calcium ions, which induce a reversible conformational change in the connexin molecules, which leads to the closure of a channel at its extracellular surface.