Previous studies on MDCK II (Madin–Darby canine kidney), rat Sertoli (the key structure of blood-testis barrier) and ADPKD (autosomal dominant polycystic kidney disease) cell cultures demonstrated that nanomolar ouabain induces the expression of claudin-1, -2, -4 and -11 [20,21,22]. Here, CLDN1 is linked to autosomal dominant polycystic kidney disease.