ATP1B1 and autosomal dominant polycystic kidney disease: Adult human RPE has an apically positive TEP of 3.5 mV.4 The TEP is an inherent property of transporting epithelia and arises from spatial variations in ion pumps, channels and leak conductances across layers of cells.5 The Na+/K+‐ATPase and cell‐cell tight junctions are important in the generation and maintenance, respectively, of the TEP and incorrect localization of Na+/K+‐ATPase can cause disease, for example autosomal dominant polycystic kidney disease.46, 47 We found ATP1B1 expression was reduced in aged mice and mice with AMD.