Fig. 5. Sgk1-dependent phosphorylation of Nedd4-2 controls ENaC cell surface expression. Oocytes were co-injected with cRNA encoding FLAG-tagged ENaC together with either H₂O, wild-type or mutant Nedd4-2 lacking both phosphorylation sites [Nedd4(S-A)₂] and Sgk1, as indicated. Amiloride-sensitive Na⁺ currents (filled bars) and binding of iodinated anti-FLAG antibodies (non-filled bars) to quantitate the number of channels at the cell surface were measured in the same oocytes, as described previously (Firsov et al., 1996; Abriel et al., 1999). Current and binding values were normalized to control values (ENaC + H₂O). n = 18 oocytes from three animals; *p <0.05 versus control, **p <0.01 versus Nedd4-2 + Sgk1.