Fig. 3. Effect of reducing the extracellular NaCl concentration on E_m, R_in and the generation of action potentials. (A) Continuous recording showing the effect of reducing the extracellular NaCl concentration by 40 mmol l^–1 for 5 min. Upward deflections are spontaneous action potentials, downward deflections were caused by the injection of negative current (–5 nA, duration 1 s, pulse interval 10 s). (B) Segment of the trace in A on an expanded time scale, shortly before and after the reduction of the extracellular NaCl concentration, as indicated. Action potentials truncated due to high gain. Note the partial recovery of the current-induced hyperpolarization (`depolarizing sag', arrow), which is due to the activation of hyperpolarization-activated (I_h) channels. (C) R_in calculated from the current-induced hyperpolarization shown in B.