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Second messengers regulate endosomal acidification in Swiss 3T3 fibroblasts
K Zen1, J Biwersi, N Periasamy
1Department of Medicine, University of California, San Francisco.
The Journal of Cell Biology
|October 1, 1992
Summary
Researchers developed new methods to measure endosomal pH, revealing that endosome acidification is influenced by anion composition, Na/K pump activity, and cellular signaling pathways.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- Endosomal acidification is crucial for cellular processes like sorting, activation, and degradation.
- Accurate pH measurement in individual endocytic vesicles is essential for understanding these processes.
Purpose of the Study:
- To develop and validate a novel methodology for quantitative pH measurement in individual endocytic vesicles.
- To investigate the factors influencing endosomal acidification, including ligand type, anion composition, and intracellular signaling.
Main Methods:
- Utilized fluorescent probes (tetramethylrhodamine, carboxyfluorescein, dichlorocarboxyfluorescein) for pH sensing (pH 4-8).
- Employed ratio imaging with a cooled CCD camera and advanced image analysis software.
- Labeled endosomes with transferrin (Tf), alpha 2-macroglobulin (α2M), or dextran to track different endocytic pathways.
Main Results:
- Developed a method for pH measurement in individual endosomes with >0.2 U accuracy.
- Transferrin-labeled endosomes acidified to pH 6.2, while dextran- and α2M-labeled endosomes acidified to pH 4.7.
- Endosomal acidification was sensitive to external anions, Na/K pump inhibition (ouabain), and second messengers (vasopressin, PMA, protein kinase A activators).
Conclusions:
- Established a robust methodology for quantitative endosomal pH measurement.
- Demonstrated that endosomal acidification is a dynamic process regulated by multiple cellular factors.
- Provided insights into the differential acidification kinetics of various endocytic pathways.