PRIMARY-CELL CULTURES FROM MURINE KIDNEY AND HEART DIFFER IN ENDOSOMAL PH

Endosomal and lysosomal pH values have been determined for many establ ished cultured cell lines of different origins. These cell lines may b e grouped into two classes based on observed differences in pH of earl y (recycling) endosomes. Members of the first class typically have an early endosomal pH of 6.2, whereas members of the second class typical ly have an early endosomal pH of 5.4. Because established cell lines m ay have developed artificial differences in endosomal pH due to extend ed culture, it remains to be determined if endosomal pH differences ex ist in vivo and whether they are functionally significant. To address this question, we generated adherent primary explants from mouse kidne y (primarily epithelial cells) and heart (primarily fibroblasts and ca rdiac muscle cells). Interestingly, enhanced acidification was observe d in heart cell endosomes (pH = 5.5) compared with kidney cell endosom es (pH = 6.0). These results indicate that differences in endosomal pH do not solely arise from extended cell culture and imply that such di fferences may be important for the proper functioning of different cel l types. (C) 1998 Wiley-Liss, Inc.