Intracellular Na⁺ and K⁺ contents of oocytes expressing wt or mutated hAE1. Na⁺ and K⁺ contents were measured in oocytes either noninjected (NI) or injected with the cRNA indicated on x-axis, 2 days after incubation in media containing 0.5 mM ouabain and 5 μM bumetanide. White bars represent Na⁺ and black bars represent K⁺ contents of oocytes. (A) Oocytes were incubated in control MBS containing Na⁺. (B) Oocytes were incubated in MBS where Na⁺ was totally replaced by impermeant cation NMDG. Data are expressed in micromole of ions per gram of dry weight and are means (± SEM) of 5 experiments (each of them made with 15 oocytes except for mutants D705Y [n = 4] and S731P [n = 3]).