Fig. 4.

Duration dependence of the use-dependent block of rNav1.4 wild-type Na⁺ currents induced by 100 μM ranolazine. A, repetitive pulses were applied as described in Fig. 3A, except that the pulse duration was shortened to 1 ms. Representative traces of Na⁺ currents were recorded and labeled with the corresponding pulse number. B, repetitive pulses with durations of 0.5, 2, 4, 10, and 20 ms were applied, and Na⁺ currents were recorded as shown in Fig. 4A. Peak currents were measured and plotted against the pulse number. Notice that the block reaches the same level with pulse duration as short as 2 ms. Data in A and B were obtained from the same cell. Comparable results were recorded in 5 cells.