Fig. 4. (A) Voltage trace from a collecting tubule cell illustrating the effect of high [K⁺] in bath, and of 1 mmol l^-1 BaCl₂ in bath control solution and in high [K⁺] solution, on V_bl. Basally applied Ba²⁺ depolarized V_bl. In the presence of Ba²⁺ the high [K⁺] solution did not depolarize V_bl further. (B) Summary data showing the effect of high [K⁺] solution, and of 1 mmol l^-1 BaCl₂ in bath control solution and in high [K⁺] solution, on V_bl. Ba_b, Ba²⁺ in bath; C, control solution; K_20,b, high [K⁺] in bath.