Figure 4. Voltage-dependent blockage of inward Na⁺ current by intracellular Rb⁺ and Cs⁺ ions in T359A and T360A mutant channels.

A, T359A current recordings from excised-patch in Na⁺ symmetrical conditions and when intracellular Na⁺ was replaced by an equimolar amount of Cs⁺. Recording conditions as described in Fig. 2. Dashed line indicates 0 current level; arrows indicate the −100 mV Na⁺ current level in symmetrical conditions. B, as in A, but for T360A mutant channel. C, I–V curves in T359A mutant channels in the presence of 110 mm intracellular Na⁺ (filled squares), and Cs⁺ (open circles). D, as in C, but for T360A mutant channel. E, dependency of I_Rb/I_Na on voltage for WT (filled circles), T359A (open squares) and T360A (filled squares), respectively (n≥ 5). F, as in E, but when intracellular Rb⁺ ions were replaced with Cs⁺ (n≥ 6).