Imaging MDA-MB-436 cells loaded with the pH-sensitive dye SNARF, we find a relatively high pHi of 7.68 ± 0.21, which is common in cancer cells [13, 14] that is decreased to pHi 7.42 ± 0.04 in the presence of EIPA (10 μM, 24 h), a selective pharmacological inhibitor of the plasma membrane H + extruder NHE1 (Fig. 5A and Supplementary Fig. S4A). The gene discussed is SLC9A1; the disease is cancer.