Fig. 1. OK and OK/NHERF2 cells were selected by acid suicide to be NHE3 null. OK cells, which had been cloned to remove fibroblast contamination (Noel et al., 1996), were selected by acid suicide (see Materials and Methods). The intracellular pH_i was measured with BCECF over time, following acidification by NH₄Cl pulsing (Levine et al., 1993). Arrow indicates Na⁺ addition. AS refers to acid suicide. NHE3 null OK cells were used for transient transfection.