The possible branching pathways connecting main functional states visited by MscS in excised inside-out patches. (A) The channel undergoes a direct C→O transition, adaptive closure (O→C_A) because of midpoint shift, from where the channels inactivate in a tension-dependent manner. Upon tension release, the channels obligatorily go to the C_A state first and then recover completely. (B) Under tension, especially gradually imposed, channels first adapt (C→C_A) and then open (C_A→O). Channels remaining in the C_A state (not open) gradually escape to the I state. Further adaptive shift of activation curve will add to the C_A population from the O state (O→C_A). Because the recovery rate is strongly tension dependent and channels refuse to recover unless tension is very low, it is conceivable that there is more preferential return to the C state as opposed to the C_A state. Note that the C_A state may not be just a pre-stressed state of the channel by tension, but rather a state of the surrounding membrane with a distorted tension profile (Belyy et al., 2010b). The positions of the state wells on the expansion coordinate are shown by letters (C, C_A, O, and I), and the approximate positions of rate-limiting barriers are designated by asterisks. The area change for the opening transition is taken from Belyy et al. (2010b).