Fig. 6. Membrane currents under isotonic and hypotonic conditions. (A) Superimposed membrane currents upon shifting E_m for 1 s from –50 mV to values ranging from –120 to –40 mV (10 mV increments, 5 s intervals) under isotonic conditions (SLS) and after 5 min in hypotonic solution (–40 mmol l^–1 NaCl). Subtraction of the current needed under isotonic conditions from the respective current under hypotonic conditions isolated the swelling-activated membrane current (`Difference'). The dependence of this current on E_m is shown in B. The traces are means of 34 experiments. Before averaging, the single traces were filtered through an 8-pole Bessel filter (100 Hz). The performance of the voltage-clamp protocol took 1 min; in the meantime, the recording system was in the current-clamp mode. (B) Voltage dependence of the averaged swelling-activated membrane current under control conditions (see A), in Cl^––free solution and in the presence of 0.5 mmol l^–1 DIDS. Data are means ± s.d. of N=47 (control, included are 13 experiments with a clamp duration of only 0.5 s), N=7 (Cl^– free) and N=11 experiments (DIDS). Arrowhead indicates the reversal potential of the swelling-activated current under control conditions.