FIGURE 3.

Rb⁺ reduces the unitary amplitude and increases the mean open time of Kv4.1 channels. (A) and (B) Consecutive Kv4.1 unitary current traces evoked by the pulse protocol shown in the lower part of these panels. Both recordings are from the same inside-out patch. K⁺ (symmetric 98 mM K⁺) or Rb⁺ (bi-ionic conditions) mediated the currents. Recordings were low-pass filtered at 1.5 kHz and digitized at 5 kHz. The solid line across the traces represents the zero current level. (C) Amplitude histogram derived from the complete data set sampled in A and B. Shaded and unshaded histograms are from K⁺ and Rb⁺ currents, respectively. The solid lines represent the best-fit Gaussian functions with the following parameters: μ = 0.56 pA and σ = 0.13 pA, for the K⁺ currents; μ = 0.45 pA and σ = 0.1 pA, for the Rb⁺ currents (μ and σ are the mean and standard deviation, respectively). (D) Histogram of open intervals derived from the complete data set sampled in A and B. Shaded and unshaded histograms are from K⁺ and Rb⁺ currents, respectively. The solid lines represent the best-fit biexponential functions with the following parameters: τ_LONG = 3.2 ms, w_LONG = 0.3, τ_BRIEF = 0.9 ms, and w_BRIEF = 0.7 for K⁺ currents; τ_LONG = 7 ms, w_LONG = 0.4, τ_BRIEF = 1 ms, and w_BRIEF = 0.6 for Rb⁺ currents (τ and w are the mean open time and the relative weight, respectively). Average values from different patches are given in Table 2.