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] = m^{3}h
- G_{Na} = Nγm^{3}h,
- 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 τ_{m} but the actual data doesn't agree