The H+/Cl- exchange transporters CLCN4 (Kawasaki et al. 1999, Zdebik et al. 2008), CLCN5 (Zdebik et al. 2008) and CLCN6 (Neagoe et al. 2010) mediate the exchange of endosomal Cl- for cytosolic H+ across endosomal membranes, contributing to the acidification of endosomes.