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