A, control hH1 currents in 0 mm external sodium. B, AC-modified currents in 0 mm external sodium. The channels were modified by perfusing the cell with 100 μm AC (in 0 mm external sodium solution) and delivering 50 pulses to −10 mV. C, AC-modified hH1 currents in 130 mm external sodium solution (same cell). Note the sustained inward currents (arrow) during voltage steps ranging from −90 to −70 mV. Scale, 1 nA, 2 ms.