Figure 5.

Block of inward K⁺ currents by external Na⁺. (A) Inward K⁺ currents, evoked by a 130-ms depolarization to 0 mV, in the presence and absence (control and recovery) of 100 mM external Na⁺. The external solution contained 3 mM K⁺ and 165 mM Tris⁺. The internal solution contained 140 mM Tris⁺. (B) Fractional K⁺ current as a function of external [Na⁺]. Symbols represent mean of 4–10 cells tested, with at least two Na⁺ concentrations being tested on each cell. All error bars are plotted. Peak currents were measured either at 0 mV (•) or 210 μs after repolarization to −60 mV (▪; tail currents were digitized at 70 μs/point). (B, solid lines) Block of K⁺ currents by external Na⁺ under the exact conditions of these experiments, predicted by the model in Fig. 4 A.