Figure 12.

Spring effect of the AC region in channel gating. In the absence of bound Ca²⁺ and in the closed conformation, the AC region adopts a conformation that inhibits channel opening. Ca²⁺ binding (+Ca²⁺) or channel opening by depolarization (+V) removes this inhibition, rendering the channel gate more favorable to the open conformation. In the open conformation or when the Ca²⁺ binding sites are occupied, the AC region has little effect on channel gating.