Gating schemes. (A) The C-O model. C, closed; O, open. (B) The COSB model. Small circles represent partial (green) and complete (red) blocking sites. (C) Allosteric model with four voltage-sensing J gating particles (orange half-circles). R, resting; A, activated. Intermediate configuration states are not depicted. (D) Two-populations model. The two pore species (1 and 2) have different conductances and gating charges.