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Flashcards

Structure and Function of Ion Channels

William Chapman Developmental and Celluar Physiology of the Specialised Cell 2nd Year English 70 cards

describe the 2-electrode voltage clamp

Cards in this deck (70)

  1. 1what is passive transport?a 'downhill' process via diffusion or osmosis
  2. 2what is active transport?'uphill' process that requires ATP energy
  3. 3name a way to prevent an action potentialremove Na+ - prevents an action potential
  4. 4what is facilitated diffusionspontaneous passive transport of ions or molecules via specific transmembrane integral proteins
  5. 5how does secondary active transport work? what is the difference with primary active transport?uses energy from the movement of one molecule down it's concentration gradient to move another against its concentration gradient
  6. 6what is antiport?one molecule moves down concentration gradient and this energy can be used to move another molecule against its concentration gradient in the opposite direction
  7. 7what is symport?downhill movement of one species to facilitate the movement of another species in the same direction but against its concentration gradient
  8. 8will water cross a hydrophobic membrane? is this the reason for aquaporins?no, yes
  9. 9can aquaporins open or close?no
  10. 10how are aquaporins selective to water molecules?interaction of channel proteins with the water molecules
  11. 11how is the ionic gradient setup and maintained?the Na+-K+ ATPase pump
  12. 12how many sodium and potassium ions does it shift each cycle?3 Na+ out, 2 K+ in against their concentration gradient each cycle
  13. 13what is the range of a typical resting membrane potential?-40 - -70 mV (depending on cell type)
  14. 14what is meant by electrochemical gradient in a resting cell?there is an electrical gradient as well as a concentration gradient. there is a negative gradient from inside to out
  15. 15what is capacitance?charge differences across the membrane and the ability of the membrane to store charge
  16. 16extracellular and intracellular concentrations of sodium, potassium and calcium?Na+ = 20mM inside and 145mM outside
    K+ = 150mM inside and 4mM outside
    Ca2+ = 0.0001mM inside and 2.5mM outside
  17. 17what happens if an ion channel opens?ions can flow across a membrane as a current
  18. 18what happens to resistance when you increase Po?reduce resistance as you increase the conductance
  19. 19what is Ohms law?V = IR
  20. 20what does adding a 'gate' do to an ion channel?makes it semi-permeable and gives it 'open' and 'closed' states
  21. 21how is pore selective?structure and size - aids passage of only specific ions
  22. 22how does lidocaine (local anaesthetic) disrupt ion flow? which ion does it affect?use - dependent block of Na+ channels
  23. 23what is the difference between sodium and potassium membrane potential curves in an action potential?potassium's peak is shifted to the right and is lower than that of sodium
  24. 24as an ion moves, the balance of electrical charge changes across the membrane, what does this affect?the driving force for the ion
  25. 25what is the equilibrium potential of the major ions?K+ = -95mV
    Na+ = +61mV
    Ca2+ = +137mV
    Cl- = - 65mV
  26. 26what does the Nernst equation calculate?the equilibrium potential of a specific ion
  27. 27what is the Nernst equation?Eion = RT/ZF * ln[ion]out/[ion]in
  28. 28what does the R stand for? Z? F?R = gas constant (8.31 kJmol/degrees K )
    Z = ionic charge
    F = Faraday Constant
  29. 29what does RT/ZF usually equal?61.5
  30. 30what do ion channels represent in an electrical circuit?a variable resistor
  31. 31how is the transmembrane electrical field created?the variably permeable membrane 'stores' charge via. ion/charge separation
  32. 32what does the goldman hodgkin-katz equation allow you to predict?the resting membrane potential for that particular cell
  33. 33what is the HH equation?look in lecture notes
  34. 34what are the three variables of the Hodgkin-Huxley Model and what is the models's purpose?model to recreate the properties of an action potential
    kinetic variable, n, which has voltage dependence
    activation variable, m
    inactivation variable, h
  35. 35describe the 2-electrode voltage clampuse xenopus oocyte as they are very large.describe the 2-electrode voltage clamp
  36. 36characteristics of whole-cell patch clamp?mild suction and tight gigaseal contact between pipette and membrane
    strong pulse of suction leads to the cytoplasm being continuous with the pipette interior
    can use as a tool to introduce channel blockers and change ionic concentrations
    sum of all channel activities of the membrane
  37. 37what is the fluorescent method of measuring changes in membrane potential?inject/ soak cell in voltage-sensitive dyes, and then shine a light source across a dichroic mirror and the emitted red light changes with membrane potential (detected by photodetector)
  38. 38on an i-v graph how can you determine the reversal potential of a specific ion?where it crosses the x - axis and there is no net ion flow
  39. 39what is the slope of the i-v curve a measure of?conductance
  40. 40what does the i-v curve of an ohmic response look like?straight line
  41. 41what does rectification mean?moves ions in only one direction and doesn't obey Ohms law
  42. 42how can we dissect whole-cell currents?channel blockers
  43. 43what does tetrodotoxin block? (TTX from puffer fish)Na+ channels
  44. 44what does saxitoxin block?Na+ channels
  45. 45what does tetraethyl ammonium (TEA) block?K+ blocker
  46. 46what do the downward and upward deflections represent?up deflections = outward movement
    down deflections = inward movement
  47. 47what are gating currents?not real currents - to do with the active channel opening and closing (artefact flicker)
  48. 48what is Ic (capacitative transient)gating currents - gating occurs with changes in the membrane potential
  49. 49what is another name of calcium activated potassium channels?BK or maxi - k channels
  50. 50what neuroscience technique shows the clustering of calcium and BK channels in hair cells?immunohistochemistry
  51. 51are cations hydrated by polar H20 molecules?yes, shells of water
  52. 52what similarities are there between ion channels and enzymes?ion channels facilitated the movement of ions at a lot lower energy
    channel facilitates the passage of a hydrophilic ion by reducing the activation energy required for the reaction to happen
  53. 53how is ion flow facilitated?by the pore substituting for water
  54. 54what techniques are there for studying ion channels?electrophysiology
    pharmacology ligands - toxins and blockers
    physiology ligands - Ach
    cloning anf sequencing proteins
    mutagenesis - mutate proteins and see what happens to their function
    antibody binding
    computer modelling - visualise structure of protein
    x - ray crystallography/ spectroscopy
  55. 55what is the role of carbonyl residues?surrogates for hydration shells in the pore
    dehydration on entrance and rehydration on exit from the pore
    as long as these are present the ion can move
    (some amino acids carry charge and some don't)
  56. 56what is the importance of a 'loose interaction' of the ion and the channel residues? (kv channels)entry of a third ion results in sufficient electrostatic repulsion to expel one K+ from opposite side
    ion repulsion prevents 'too tight' binding and so flow results - chain of ions move through pore
  57. 57what determines the selectivity of the pore?pore residues and the correct interaction with the ion
  58. 58what three ions do NMDA receptors pass?calcium
    potassium
    sodium
  59. 59what ion clogs NMDAR at resting membrane potential?Mg2+ and pops out on depolarisation (usually from AMPAR stimulation)
  60. 60give three examples of tetramer channelsvoltage gated calcium and potassium
  61. 61how many subunits does nAchR have?pentamer - 5
  62. 62is connexin a hexamer?yes
  63. 63of a 6 transmembrane receptor, which section is the voltage sensor?s4
  64. 64what is the pore domain?s5 - s6
  65. 65what is the voltage-sensitive domain?s1 - s4
  66. 66list the two nucleotide-gated channelscAMP
    cGMP
  67. 67how many pores does a K+ leak channel have?2
    they also lack a s4 region
  68. 68are K+ leak channels open at rest?yes but they are regulated by neurotransmitters
  69. 69K+ leak current role?high basal activity - set the negative membrane potential of neurons
  70. 70what does HYPP stand for?hyperkalaemic periodic paralysis

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2nd Year Developmental and Celluar Physiology of the Specialised Cell (Structure and Function of Ion Channels) Flashcards on Structure and Function of Ion Channels , created by William Chapman on 28/03/2016.
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