# 6.021/Notes/2006-12-11

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## Tail currents

- Hodgkin-Huxley cannot explain this phenomenon
- We can consider model of channel where the gate sare not statistically independent
- Instead of looking at individual gates, consider the state of the channel as a whole
- Each state has a conductance and gating charge
- If n states and probability of being in that state [math]\displaystyle{ Pr[\tilde{s}=s_n]=x }[/math],
- [math]\displaystyle{ g=E[\tilde{g}]=\Sigma \gamma_nx_n }[/math]

- Multiple channel state model with single conducting state can explain S-shaped onset of activating factor and also inactivating factors
- The slow onset is due to the intermediate states that the channel has to go through to become conducting
- Inactivation is explained by intermediate states which are more favorable to go away from that state

## Sodium channel structure

- 6 transmembrane domains
- S4 has lots of charge and mutating removes voltage gating

- Mutagenesis
- 2 amino acid mutations can convert specificity away from Na to Ca
- can mutate to eliminate inactivation