Figure 10.

Changes in the β4_154–167 time-dependent block by external Na⁺ concentration. (A) Superimposed current traces of hNav1.5-CW mutant Na⁺ channels were recorded with a bath solution containing 130, 65, or 0 mM Na⁺ ions and normalized with respect to the outward peak value. The τ values for 0, 65, and 130 mM Na⁺ ions were 0.277 (τ₀), 0.276 (τ₆₅), and 0.334 ms (τ₁₃₀), respectively. The pipette solution contained 2 mM β4_154–167. A minimal tail current was present with 0 mM external Na⁺ ions, whereas a large tail was found with 65 and 130 mM external Na⁺ ions. (B) Currents were recorded under an identical protocol, except the pipette solution contained 125 μM β4_154–167. The τ values for 0, 65, and 130 mM Na⁺ ions were 0.540, 0.697, and 0.952 ms, respectively. These experiments were repeated in five to seven cells.