Figure 10.

Effect of external Na⁺ on K⁺ current activation, inactivation, and deactivation kinetics. These currents, carried by 3 mM external K⁺, were obtained in experiments as described in Fig. 5. (A) Two normalized traces are superimposed, one obtained in the absence of external Na⁺, one obtained in the presence of 100 mM external Na⁺. In this cell, 100 mM Na⁺ blocked the K⁺ current by 42% at 0 mV. The activation time course for both currents was well-fit by a single exponential function, with time constants of 16.84 ± 1.87 and 18.50 ± 2.25 ms, in the absence and presence of Na⁺, respectively (n = 5). (B) Two normalized tail currents (solid lines) are superimposed, recorded in the absence and presence of Na⁺. Also superimposed on these currents are double exponential fits (dashed lines), which yielded identical fast and slow time constants under the two conditions (τ₁ = 5.98 ± 0.43 and 4.81 ± 0.62 ms, respectively; τ₂ = 2.49 ± 0.56 and 1.29 ± 0.49 ms, respectively; n = 5). In this cell, 100 mM Na⁺ blocked the tail current by 49%. The horizontal dashed line represents the 0 current baseline.