# 6.021/Notes/2006-12-11

## 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 $\displaystyle{ Pr[\tilde{s}=s_n]=x }$,
• $\displaystyle{ g=E[\tilde{g}]=\Sigma \gamma_nx_n }$
• 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