6.021/Notes/2006-12-04

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] = $m 3 h$
- $G N a = N γ m 3 h$ , $\overline{G_{Na}}=N\gamma$
- 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 $τ m$ but the actual data doesn't agree