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] = $$m^3h$$
 * $$G_{Na} = N\gamma m^3h$$, $$\overline{G_{Na}}=N\gamma$$
 * 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 $$\tau_m$$ but the actual data doesn't agree