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Estimation of pH in individual alveolar macrophage phagolysosomes
K Nyberg1, U Johansson, I Rundquist
1Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.
Abstract:
A method for measurement of phagolysosomal pH in individual alveolar macrophages based on a cytofluorometric technique with fluorescein-labeled silica particles (FSP) as a probe was developed. The size of the FSP, 3.0 or 5.0 microns, did not affect the result of the pH measurements. The average pH values, range 5.1-5.5, of individual particles in macrophages from three rabbits agreed well with the pH values obtained in a macrophage population using a fluorescence spectrometer and the FSP. The variation of pH in phagolysosomes in alveolar macrophages from five rabbits was investigated. Measurements were performed 3, 6, and 24 h after addition of the FSP in cells containing one particle as well as in cells containing two particles. The variation in pH was small, with a coefficient of variation less than 10% in all rabbits at all times. There was a significant correlation between values obtained from two phagolysosomes in the same cell, indicating a cell factor responsible for 10-30% of the total variance. The fact that the variation of pH is small in normal, untreated rabbit alveolar macrophages should be of importance when estimating alveolar clearance of inorganic particles due to dissolution in the acid phagolysosomal milieu.
Insights
A new method accurately measures phagolysosomal pH in individual alveolar macrophages using fluorescein-labeled silica particles (FSP). This technique reveals consistent pH levels, crucial for understanding particle clearance in the lungs.
Area of Science:
- Cell Biology
- Immunology
- Respiratory Medicine
Background:
- Alveolar macrophages are key immune cells in the lungs.
- Phagolysosomal pH is critical for macrophage function and particle clearance.
- Accurate measurement of phagolysosomal pH in individual cells is challenging.
Purpose of the Study:
- To develop and validate a cytofluorometric method for measuring phagolysosomal pH in individual alveolar macrophages.
- To assess the variability of phagolysosomal pH in rabbit alveolar macrophages.
- To investigate the influence of particle load on phagolysosomal pH.
Main Methods:
- Developed a cytofluorometric technique using fluorescein-labeled silica particles (FSP) as pH probes.
- Measured phagolysosomal pH in individual alveolar macrophages from rabbits.
- Varied FSP size (3.0 or 5.0 microns) and particle load (one or two FSP per cell).
- Assessed pH at 3, 6, and 24 hours post-FSP addition.
Main Results:
- The FSP method provided reliable pH measurements, consistent with population-based fluorescence spectrometry.
- Average phagolysosomal pH ranged from 5.1 to 5.5.
- Minimal pH variation was observed (coefficient of variation <10%) across rabbits and time points.
- A cell-specific factor contributed 10-30% to the total pH variance.
Conclusions:
- The developed cytofluorometric method is effective for measuring individual phagolysosomal pH.
- Normal rabbit alveolar macrophages exhibit stable phagolysosomal pH.
- This stability is important for accurately estimating alveolar clearance of inorganic particles via dissolution.