Figure 5. Stimulation by aldosterone (2.5 h) of I_p produced by pumps containing different α-subunits at 10 mM (I_P10) and 90 mM (I_P90) Na⁺.

Original recordings are shown in the left panels. I_p was induced by the addition of 10 mM (A and B) and 90 mM (C and D) Na⁺. I_p carried by endogenous pumps was then blocked by the addition of 50 μM strophanthidin (continuous arrow). I_p carried by pumps containing an exogenous subunit was subsequently blocked by the addition of 3 mM ouabain (dotted arrow). Cell lines expressing rα1 are shown in A and C and cell lines expressing rα2* are shown in B and D. The right-hand panels show the mean fractional changes in I_p (aldosterone (▪) vs. control (□)) carried by pumps containing endogenous (endo) and exogenous (exo) α-subunits, respectively, measured in 8, 12, 7 and 4 paired experiments (A-D). Mean total I_P10 (I_P90) in cell lines expressing rα1 and rα2* was 0.38 ± 0.06 μA cm⁻² (5.17 ± 0.32 μA cm⁻²) and 0.30 ± 0.02 μA cm⁻² (5.02 ± 0.78 μA cm⁻²), respectively, in control epithelia and 0.71 ± 0.09 μA cm⁻² (5.83 ± 0.50 μA cm⁻²) and 0.46 ± 0.03 μA cm⁻² (4.84 ± 0.86 μA cm⁻²) in aldosterone-treated epithelia.