Fig. 6.

Effect of PI(4)P and PI(4,5)P₂ on the Na⁺ sensitivity of the channel. A–C, Representative samples of single-channel activity induced by the concentration of Na⁺ indicated before (A) and during exposure to either 4 μm PI(4,5)P₂ (B) or 4 μm PI(4)P (C).Traces in A–C were obtained from different patches. Traces in B andC were recorded at least 5 min after the addition of phosphatidylinositols. D, Plot of the open probability (ordinate) as a function of Na⁺concentration (abscissa) in the absence (filled triangles) and presence of either 4 μm PI(4,5)P₂ (filled circles) or 4 μm PI(4)P (open squares). Data points obtained from 1 min recordings (n = 4). Solid lines represent fits of Hill equations (see Fig. 4) with the following parameters: EC₅₀ (in mm), 67.0 ± 5.0 in control, 22.4 ± 16.7 for PI(4,5)P₂, and 8.1 ± 0.5 for PI(4)P; y₀/(y₀ +y₁), 0.00 ± 0.06 in control, 0.45 ± 0.04 for PI(4,5)P₂, and 0.07 ± 0.01 for PI(4)P; and k, 2.7 ± 0.5 in control, 1.0 ± 0.6 for PI(4,5)P₂, and 1.3 ± 0.2 for PI(4)P. The parameters are given as mean ± SE. For illustration clarity, the data points were normalized by the sum of y₀and y₁ obtained from the fits.