Fig. 1. (A) Current traces for the Escherichia coli MscS and MscL channels recorded at a pipette voltage of +40 mV and +30 mV, respectively. C and O_n designate closed and open levels of n channels. (B) Boltzmann distribution curves for MscS and MscL. A Boltzmann distribution function of the form P_o/1–P_o=exp[(p–p_1/2)] of the channel open probability P_o plotted against suction p was calculated from the traces shown in A. (mmHg^–1) is the slope of the plot ln[P_o/(1–P_o)] versus suction and describes the sensitivity to negative pressure of the channels, whereas p_1/2 (mmHg) is the negative pressure at which P_o equals 50% (1 mmHg=133 Pa). Adapted with permission from Elsevier (Martinac and Kloda, 2003). (C) Comparison of structures of the MscL and MscS channel. MscL forms homopentameric channels (Chang et al., 1998), whereas MscS is a homoheptamer (Bass et al., 2002). Colours indicating different structural elements are shown along the centerline of each channel molecule. Reproduced with permission from the American Association for the Advancement of Science (Bezanilla and Perozo, 2002). CYT, cytoplasmic region; TM, transmembrane region.