Catalytic activity of CAP2 is required to stimulate ENaC. (A) INa stimulated by CAP2 is sensitive to aprotinin. Eggs coexpressing ENaC plus CAP2 were preincubated or not with 50 μg/ml aprotinin overnight (n = 18). ENaC WT plus CAP2 versus ENaC WT plus CAP2 plus aprotinin. *, P < 0.0001. (B) Inactive CAP2 s387a (CAP2s387a) does not activate ENaC. Amiloride-sensitive INa stimulated by WT but not by inactive CAP2 (n = 30). (A and B) Batches of oocytes were extracted from four to five different frogs. Results are expressed as the means ± SE. *, P < 0.0001. Statistical significance was determined using an unpaired Student's t test. (C) Inactive CAP2 is expressed as a full-length precursor. Western blots of WT and inactive express-tagged CAP2. Representative experiment is shown.
