Figure 10.

Li and K currents carried by veratridine-modified Na channels. For both Li and K currents, the decaying components of inward currents are substantially larger than the reverse currents that develop upon removing the extracellular cations. (A) NMDG was substituted for 120 mM Li. 25 µM veratridine then rapidly activated a 0.55 nA inward current that decayed with a τ of ∼20 s. The mean for the decay phases was 18.1 s, and the mixing volume is estimated to be 7.5 pL. (B) NMDG was substituted for 120 mM K, and 25 µM veratridine application then activated a 0.30 nA inward current. When activated by applying extracellular K, the current decayed partially with a τ of 9.2 s. The mean τ was 11.1 s, and the mixing volume is estimated to be 6.0 pL.