Forces governing voltage sensor pore coupling. (A) Voltage sensor pore coupling can be attractive. The voltage sensor in up conformation can pull the pore gates, which intrinsically tend to be closed, open. (B) The voltage sensor–pore interaction can be repulsive where the voltage sensor in resting state prevents the pore from opening. In this case, the pore intrinsically tends to be open, and repulsive forces between the two domains keep it closed when the voltage sensor is down conformation. The arrows show the direction of the forces. Note that these two forces are not necessarily exclusive because they occur in different conformations, and in theory they can both exist at the same time.