FIGURE 5.

Effect of the cytosolic K⁺ on the voltage dependence of the FV channel. Macroscopic FV current-voltage relations for 100-mM vacuolar K⁺ and variable cytosolic K⁺ as ones presented in Fig. 1 a were divided by corresponding single-channel current-voltage relations (Fig. 4) resulting in the mean number of open FV channels as the function of the voltage. Mean number of channels open at +100 mV in symmetric 100 mM K⁺ was taken as a standard equal to 1 for each individual cytosolic side-out patch, and other data were scaled accordingly. The data for each cytosolic K⁺ concentration obtained on n separate patches are averaged and presented as mean ± SD as a function of voltage. Symbols for 10 mM (filled circles, n = 7), 30 mM (triangles, n = 5), 100 mM (hollow circles, n = 8), and 400 mM (squares, n = 5) cytosolic K⁺; 10 mM K⁺ plus 90 mM NMDG⁺ (asterisks, n = 6). Solid lines are best fits to the Eq. 1 given in Materials and Methods, with values of parameters V₁ and V₂ plotted in Fig. 7 a.