Figure 4. The ASIC-like current is carried mainly by Na⁺.

A, both the ASIC-like current (upper left panel) and the voltage-activated Na⁺ current (upper right panel) reversed the direction of current flow at approximately the same potential (lower panel) in a representative cell. The ASIC-like current was activated by a 5 s pH step to 6.4 at holding potentials of −72, −52, −32, −12, −2, +8, +18, +28 and +48 mV (from bottom to top, respectively). The voltage-dependent Na⁺ current was activated by stepping to more depolarised potentials between −72 and +38 mV at 10 mV increments. Both currents had zero amplitude near +10 mV as indicated by the arrows. Note that the amplitude of ASIC-like current was magnified 10 times for better comparison. B, the averaged current–voltage relation indicated a reversal potential of ∼+13 mV, close to the predicted reversal potential of +19 mV for a Na⁺-selective channel. Each data point represents the mean ±s.e.m. of 7 cells.