Fig. 4.

(A) The effect of symmetrical pH on the magnitude of the initial rate of flux through the M2 channel in response to a K⁺/valinomycin-induced potential of 62 mV. Circles: K-containing M2PLs (Fig. 3A); triangles: Na-containing M2PLs (Fig. 3B). (B) The chord conductance computed for the proton flux (open symbols) shown in A and the K⁺/valinomycin-induced potential of 62 mV at t = 0. (Note that the valinomycin allows distribution of potassium ions at a rate much greater than proton flux so that the full potential is essentially formed at time = 0). Also shown in B is the value of the chord conductance for Na⁺ ions vs. pH_in (closed symbols—circles: K-containing M2PLs; triangles: Na-containing M2PLs). The Na⁺ conductance was computed between t = 6 min and 10 min during which the pH changed relatively slowly, allowing computation of the mean V and E_Na⁺ over this interval (see SI Text).