Patch-clamp electrophysiology was used to assess ENaC activity in isolated, split-open rat cortical collecting duct (CCD). CCDs were isolated from Dahl SS rats as described previously (Pavlov et al., 2013, 2015b). Kidneys were cut into thin slices (< 1 mm) then placed into ice-cold physiologic saline solution (pH 7.4). Collecting ducts were mechanically isolated from these slices by micro-dissection using forceps under a stereomicroscope. CCDs were split open with sharpened micropipettes controlled with micromanipulators to gain access to the apical membrane.