Figure 13.

Lifetimes of blocked (A) and reciprocal unblocked (B) events as a function of internal Ba²⁺ concentration in PE and PS bilayers. (A) Mean values of short (circles) and long (squares) lifetimes of Ba²⁺-blocked events in PE (filled symbols) and PS bilayers (open symbols) measured at various concentrations of external Ba²⁺ in the presence of symmetrical 100 mM KCl. (B) Mean values of the reciprocal lifetime of unblocked events at different concentrations of internal Ba²⁺ and symmetrical 100 mM KCl. Solid lines are linear fits used to obtain the association rate constant for slow block by internal Ba²⁺ as given in the text. The dotted lines are theoretical curves plotted according to τ_U ⁻¹ = k_on[Ba²⁺]_local + b, showing the behavior expected for a process governed by the measured association rate (k_on) in PE and the expected local concentration of Ba²⁺ at various distances in Å from a bilayer containing 80% PS as calculated from GCS theory (materials and methods).