FIGURE 5.

ENaCs with the βC43A,C557A mutation exhibit reduced P_o. A, Na⁺ self-inhibition was assessed in oocytes expressing WT αβγ or the mutant αβC43A,C557Aγ. Whole cell currents were measured with oocytes bathed in a low [Na⁺] solution (white bar, 1 mm Na⁺ (sodium was replaced with N-methyl-d-glucamine)) and subsequently bathed in a high [Na⁺] solution (black bar, 110 mm Na⁺). Representative current tracings are shown. B, the ratios of the steady state (I_ss) to peak (I_peak) currents reflect the extent of the Na⁺ self-inhibition response (mean ± S.E., *, p < 0.02, n = 16–18). C–E, cell attached patch clamp recordings were obtained from oocytes expressing αβγ or αβC43A,C557Aγ. Patches were clamped at −100 mV (membrane potential). Both bath and pipette solutions contained 110 mm Na⁺. Recordings containing single channels lasting for at least 5 min were selected for analysis. Representative recordings of single channel currents are shown in C where the letters C and O represent closed and open states, respectively. The scale bars indicate current amplitude (pA) and time (minutes). P_o was determined as described under “Experimental Procedures” and presented in D for multiple experiments (n = 6) and as the mean ± S.E. in E. The P_o for αβC43A,C557Aγ (0.17 ± 0.06) was significantly lower than that determined for WT αβγ (0.45 ± 0.08) (*, p = 0.02, n = 6).