Figure 9. Concentration and voltage dependence of ${\text{K }}_{\text{o}}^{+}$ effects on Kv1.5 Na⁺ currents in 130 mM ${\text{N }}_{\text{i}}^{+}$/5 mM ${\text{N }}_{\text{o}}^{+}$.

A, time constants of current decay as a function of ${\text{K }}_{\text{o}}^{+}$ on a logarithmic scale. Data represent means ±s.e.m. (n = 4-12). B, ratio of decay time constant in K⁺-containing solution (τ_K) over that in K⁺-free solution (τ_Na) against depolarization voltage. •, 0.1 mM ${\text{K }}_{\text{o}}^{+}$ data (n = 5-8); ^, 2 mM ${\text{K }}_{\text{o}}^{+}$ data (n = 6–8, means ±s.e.m.). In both cases, before addition of ${\text{K }}_{\text{o}}^{+}$, Na⁺ currents were at steady state induced by 400 ms pulses from -80 to +60 mV at 0.05 Hz. The straight lines fitted through the data had a slope of -0.01 for 0.1 mM ${\text{K }}_{\text{o}}^{+}$ and -0.3 for 2 mM ${\text{K }}_{\text{o}}^{+}$. C, voltage dependence of use dependence of conductance in 2 mM ${\text{K }}_{\text{o}}^{+}$. Cells were pulsed to a range of potentials at 0.05 Hz and steady current conductance was normalized to peak (first pulse) conductance (g_steady/g_peak). Different cells were used for each potential, n = 4–11.