Fig. 3. Recordings showing the effect of a reduction of bathing saline K⁺ concentration from 20 to 2 mmol l^–1 (A), Cl^– from 158.5 to 15.85 mmol l^–1 (B) and Na⁺ from 132.5 to 13.25 mmol l^–1 (C) on V_bl before and after addition of 6 mmol l^–1 Ba²⁺. The tubules were exposed to the different conditions for the periods indicated by the horizontal bars. The spikes in the voltage measurements prior to treatment with Ba²⁺ were artefacts associated with movement of the experimenter.