6.021/Notes/2006-12-04

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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] = Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle m^3h}
    • Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle G_{Na} = N\gamma m^3h} , Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle \overline{G_{Na}}=N\gamma}
    • 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 Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://api.formulasearchengine.com/v1/":): {\displaystyle \tau_m} but the actual data doesn't agree