# 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