Figure 6. Effects of extracellular and intracellular Ca²⁺ on the I–V relationship of the V-ATPase current.

The pipette contained 5 mm ATP. pH_o/pH_i was 7.3/5.5. A, I–V curves for relative bafilomycin A₁ (200 nm)-sensitive currents recorded with various combinations of extracellular and intracellular Ca²⁺ concentrations, respectively, in 6 cells: 1 mm and < 0.05 μm (▪); 40 mm and < 0.05 μm (□); and 1 mm and 0.5–5 μm (▵). Data in each cell were normalized to the values at 0 mV and averaged. B, the bafilomycin-sensitive current densities at 0 mV with different intracellular Ca²⁺ levels: 0.104 ± 0.012 pA pF⁻¹ (n = 25) for < 0.05 μm; 0.091 ± 0.031 pA pF⁻¹ (n = 6) for 0.5 μm; and 0.126 ± 0.011 pA pF⁻¹ (n = 4) for 5 μm Ca²⁺. The extracellular Ca²⁺ was 1 mm. Data are means ± s.e.m.