As internalized materials progress through the endocytic pathway, they are exposed to an increasingly acidic pH. The pH of early endosomes is typically near 6, late endosomes near 5 and lysosomes even lower.

Two classes of cultured cell lines have been proposed based on their early endosomal pH (Murphy, 1988; Sipe et al., 1991). Class H lines have an early endosomal pH of 6.1-6.2 and a late endosomal pH of 5.4-5.6. Class L lines have an early endosomal pH of 5.4, similar to that of their late endosomes. Only Class H lines show an alteration in endosomal pH upon treatment with ouabain. The tables below summarize current evidence regarding the class into which given cell lines can be placed. All comments/corrections are welcome! Please send to murphy@cmu.edu.

Class H

Cultured cell line	Reference for early endosomal pH higher than late endosomal pH	Reference for lowered early endosomal pH in the presence of ouabain
Swiss 3T3	Murphy et al., 1984	Zen et al., 1992
Balb/c 3T3	Sipe and Murphy, 1987
CHO	Yamashiro and Maxfield, 1987	Fuchs et al., 1989
A549	Cain et al., 1989	Cain et al., 1989
Chicken embryo fibroblasts	Killisch et al., 1992

Class L

Cultured cell line	Reference for low early endosomal pH (~5.4)	Reference for absence of effect of ouabain on early endosomal pH
K562	van Renswoude et al., 1982; Sipe et al., 1991	Sipe et al., 1991
Sc9	Sipe, 1990	Sipe, 1990
HD3	Killisch et al., 1992

Much less work has been done on primary cell explants or cultures.

Class H

Tissue or cell type	Reference for high early endosomal pH (~6)	Reference for lowered early endosomal pH in the presence of ouabain
Primary cultures from mouse kidney	Rybak and Murphy, 1998

Class L

Tissue or cell type	Reference for low early endosomal pH (~5.4)	Reference for absence of effect of ouabain on early endosomal pH
rat hepatocytes		Anbari et al., 1994
primary cultures from mouse heart	Rybak and Murphy, 1998

---

References

Anbari, M., Root, K. V., and Van Dyke, R. W. (1994) Role of Na,K-ATPase in regulating acidification of early rat liver endocytic vesicles. Hepatology, 19: 1034-1043.

Cain, C. C., Sipe, D. M., and Murphy, R. F. (1989) Regulation of endocytic pH by the Na+,K+-ATPase in living cells. Proc. Natl. Acad. Sci. USA, 86: 544-548.

Fuchs, R., Schmid, S., and Mellman, I. (1989) A possible role for the Na+,K+-ATPase in regulating ATP-dependent endosome acidification. Proc. Natl. Acad. Sci. USA, 86: 539-543.

Killisch, I., Steinlein, P., Römisch, K., Hollinshead, R., Beug, H., and Griffiths, G. (1992) Characterization of early and late endocytic compartments of the transferrin cycle: Transferrin receptor antibody blocks erythroid differentiation by trapping the receptor in the early endosome. J. Cell Sci., 103: 211-232.

Murphy, R. F. (1988) Processing of Endocytosed Material. Adv. Cell Biol., 2: 159-180.

Murphy, R. F., Powers, S., and Cantor, C. R. (1984) Endosomal pH measured in single cells by dual fluorescence flow cytometry: rapid acidification of insulin to pH 6. J. Cell Biol., 98: 1757-1762.

Rybak, S. L., and Murphy, R. F. (1998) Primary cell cultures from murine kidney and heart differ in endosomal pH. J. cell. Physiol., 176: 216-222.

Sipe, D. M. (1990) Endosomal acidification and iron release from transferrin [Ph.D. Dissertation]. Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA.

Sipe, D. M., Jesurum, A., and Murphy, R. F. (1991) Absence of Na+,K+-ATPase regulation of endosomal acidification in K562 erythroleukemia cells. J. Biol. Chem., 266: 3469-3474.

Sipe, D. M., and Murphy, R. F. (1987) High resolution kinetics of transferrin acidification in BALB/c 3T3 cells: Exposure to pH 6 followed by temperature-sensitive alkalinization during recycling. Proc. Natl. Acad. Sci. USA, 84: 7119-7123.

van Renswoude, J., Bridges, K. R., Harford, J. B., and Klausner, R. D. (1982) Receptor-mediated endocytosis of transferrin and the uptake of Fe in K652 cells: Identification of a nonlysosomal acidic compartment. Proc. Natl. Acad. Sci. USA, 79: 6186-6190.

Yamashiro, D. J., and Maxfield, F. R. (1987) Kinetics of endosome acidification in mutant and wild-type Chinese Hamster Ovary cells. J. Cell Biol., 105: 2713-2721.

Zen, K., Biwersi, J., Periasamy, N., and Verkman, A. S. (1992) Second messengers regulate endosomal acidification in Swiss 3T3 fibroblasts. J. Cell Biol., 119: 99-110.

Last Updated: 01 Dec 2004

Copyright © 1996-2019 by the Murphy Lab, Computational Biology Department at Carnegie Mellon University