FIGURE 1.

Effect of ENaC P_o on P8 inhibition. A, effect of external [Na⁺] on P8 inhibition. Amiloride-sensitive currents were measured by two-electrode voltage clamp at −100 mV for 10 and 110 mm external Na⁺ and +40 mV for 1 mm external Na⁺ at the [P8] indicated. Values are mean ± S.D. (n = 6). Data were fit to the Hill equation. At 110 mm Na⁺, IC₅₀ = 0.8 ± 0.1 μm; at 10 mm Na⁺, IC₅₀ = 7 ± 1 μm; at 1 mm Na⁺, IC₅₀ > 100 μm. B, effect of βS518K mutation on P8 inhibition. Effect of 10 μm P8 on amiloride-sensitive currents of oocytes injected with αβγ or αβS518Kγ ENaC were measured by two-electrode voltage clamp at −100 mV. Values are mean ± S.D. (n = 5). *, p < 0.001 versus wild-type by Student's t test.