Thursday, February 27, 2014 CC-BY-NC
Ion channels

Maintainer: admin

1ionotropic channels

  • two ionotropic glutamate receptors
    • AMPA
      • fast EPSP at excitatory synapse
      • let Na+ into cell
    • NMDA
      • at resting, pore is blocked by Mg2+
      • depolarization expels Mg2+ and enable pore to conduct
      • pore lets Ca+ in
      • involves in synaptic plasticity, a process in which an excitatory synapse become stronger
  • ionotropic receptors: ion channels that open in response to binding small molecules (neurotrasnmitters)

  • GABA_A receptor

    • IPSP : inhibitory postsynaptic potential
    • binds to GABA and let Cl- in

2Metabotropic receptors

  • glutamate has AMPA and NMDA, the two ionotropic receptors, but also metabotropic gluatmate receptor (mGluR)
  • activation leads to activation of second messenger, whic activates many cellular proteins and lead to changes in activities of some trasncription factors
  • neurotransmitters that act on metabotropic receptors are often called neuromodulators
    • dopamine
    • serotonin
    • norepinephrine
    • neuropeptides : substance Y, endorphins

3Voltage gated channels

3.1Potassium channel

  • can be open or closed
  • structure

    • composes of four identical proteins
    • each protein has transmembrane domains S1, S2....S6
    • S5 and S6 forms a pore
    • S6 has GYGVT residue facing toward the pore
  • how does it select for K+ , which is bigger than Na+

    • GYGVT has carbonyl oxygen which interact with K+
    • energy required to strip away the hydroshell of K+ is regained back from the interaction
  • how does the ion contionously flow through the pore

    • the pore is occupied by two K+ ions
    • eletrostatic repulsion between the ions allow the flow of the first ion
  • how does depolarization causes it to open

    • S4 is a voltage sensing domain.
      • alternating postive and hydrophobic amino acids
      • move out to open the channel
  • how does it close

    • the N-terminus blocks it

3.2Sodum channels

  • many subtypes
  • unlike potassium which is four proteins, it's a protein with four domains, so ~4 times as long (amino acid wise) than potassium channel
  • more on its effect on pain and epilepsy next time