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Ion channels

  • Two state gate model
    • compare with Hodgkin-Huxley model
    • Only one time constant (simple exponential) in two state model
    • Can't explain inactivation
  • Use 4 gates, 3 activating, 1 inactivating
    • All independent
    • channel is open iff all gates open
    • Pr[channel open] = Pr[gate1 open]*Pr[gate2 open]*Pr[gate3 open]*Pr[gate4 open] = [math]\displaystyle{ m^3h }[/math]
    • [math]\displaystyle{ G_{Na} = N\gamma m^3h }[/math], [math]\displaystyle{ \overline{G_{Na}}=N\gamma }[/math]
    • Exactly Hodgkin-Huxley!
  • Activation is independent of inactivation
    • Also pharmacologically independent
    • Pronase only inhibits inactivation of sodium channel
  • What HH model cannot explain
    • Tail currents
    • Current that occurs at end of step should be 3 times faster than [math]\displaystyle{ \tau_m }[/math] but the actual data doesn't agree