Na+ channel gating

Figure 2. Kinetic schemes for Na channel gating (right) and the graphed time-course for single channels (solid lines, the higher position is open ) and for the population of many channels (broken line, the fraction open increases upwardly). Numbers at the arrows of the kinetic scheme are the rate constants, in 10 sec" The period of simulation is 5 msec. Computerized model courtesy of Dr. Daniel Chemoff.

Activation is slower in less depolarized membranes and inactivation drains the open (and resting) state more effectively. In fact, real Na" " channels gate by more complex pathways, including several closed states intermediate between R and O, as well as multiple inactivated states. Inactivation from these intermediate states is probably faster than from / , and the entire activation process, in its fully branched entirety, is rich with kinetic possibilities. However, the effects of toxins may be understood in general by the simpler scheme presented in Figure 2. 

---