Non‐technical summary  Most cellular processes are exquisitely sensitive to pH. Consequently our cells have a range of processes directed to control cellular pH. Plasma membrane transport proteins move acid or base across the plasma membrane to regulate pH precisely. We studied AE1 (also called Band 3) of erythrocytes and kidney cells, which rapidly transports the base, bicarbonate. AE1's high transport rate, combined with the surprisingly slow rates of H+ diffusion in cytosol, led us to wonder whether AE1 changes the pH of its local environment. The key findings were that H+ diffusion through the cytosol occurs at 0.6 μm s−1, and along the inner surface of the plasma membrane at only 0.01 μm s−1. We estimated that the size of the region of altered pH (H+ microdomain) around AE1 is 0.3 μm in diameter. pH‐regulatory transporters, like AE1, have differential effects on their immediate environment, with implications for the regulation of nearby pH‐sensitive proteins.