Figure 7.

Data from five separate mathematical approaches were used to estimate the magnitude of the pore volume change associated with activation (▪, rate kinetics; □, current ratio), inactivation kinetics (•, rate kinetics; ○, steady state inactivation) and deactivation kinetics (▴). The estimates were voltage independent. Data from the crystal structure of the open MthK channel (Jiang et al. 2002) and the open channel model of KcsA (Doyle et al. 1998; Perozo et al. 1999) were used to give an estimate the available water-filled intracellular volume of the open state: the open KcsA pore was calculated to be 7431 ų (×) and the open MthK pore was calculated to be 7852 ų (⋇).