Figure 5.

Trypsin cleavage of ENaC precludes DCA activation of the channel. A, representative whole-cell current trace of an oocyte expressing WT ENaC sequentially treated with DCA, trypsin, and then DCA again. Cells clamped at −100 mV were treated with 1 mm DCA (DCA #1) for 60 s. Following washout, oocytes were then treated with 2 μg/ml trypsin for 2 min. After removing trypsin from the bath, a second perfusion of 1 mm DCA was applied (DCA #2), followed by 10 μm amiloride (amil). Changes in current were determined by comparing steady-state currents during DCA or trypsin treatment to amiloride-sensitive steady-state currents just prior to treatment. Individual experiments are plotted with bars indicating the mean of each group (n = 8). ****, p < 0.0001 by repeated measures one-way ANOVA with the Greenhouse–Geisser correction and Tukey's post hoc analysis. B, oocytes expressing ENaC subunits lacking inhibitory tracts (ENaCΔI: αΔ206–231βγΔ144–186) were clamped at −100 mV and exposed to 1 mm DCA in the bath solution, followed by 10 μm amiloride. No effect was detected upon DCA addition (n = 11; p = not significant by paired Student's t test).