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Stimulus-permeability coupling in rat pulmonary macrophages challenged by Pseudomonas aeruginosa. An X-ray
Abstract:
Electron probe X-ray microanalysis (XRMA) of freeze-dried ultrathin sections provides the capability of measuring intracellular elemental content. This methodology was used to investigate the stimulus-permeability coupling responses associated with phagocytosis of Pseudomonas aeruginosa by cultured pulmonary alveolar macrophages (PAMs) of rats. PAMs were challenged with P. aeruginosa suspended in Gey's buffer at a bacteria to PAM ratio of 50:1 for 1 h at 37 degrees C. A 1-mm3 pellet of the unchallenged control PAMs, challenged PAMs and P. aeruginosa alone was quench-frozen in nitrogen-cooled, liquid propane, and 0.1-micron cryosections were cut at -100 degrees C. X-ray spectra were collected for nucleus and cytoplasm of 39 control PAMs, 36 challenged PAMs and 40 P. aeruginosa. Concentrations (mmole/kg dry weight) were obtained for Na, Cl, K, Ca, Mg, P, S for each cell. In the control PAMs, the content was similar to other mammalian cells. Moreover, there were no differences in elemental content between nucleus an cytoplasm. In the challenged PAMs, Na concentration was 4 times that of control PAMs (p less than 0.001) whereas Cl was double (p less than 0.001), K was 29% lower (p less than 0.001), and Ca was 4 times higher (p less than 0.05). The elemental concentration profile in the P. aeruginosa was distinctly different from that of the PAMs: higher Na, Ca, Mg, but lower Cl and K values. These results demonstrated elemental content changes in cultured PAMs challenged with P. aeruginosa that indicate a stimulus-permeability response by membranes associated with the phagocytic process.
Insights
Electron probe X-ray microanalysis revealed significant elemental changes in rat pulmonary alveolar macrophages (PAMs) during Pseudomonas aeruginosa phagocytosis. These shifts in sodium, chloride, potassium, and calcium indicate a stimulus-permeability response in cell membranes.
Area of Science:
- Cell Biology
- Biochemistry
- Immunology
Background:
- Phagocytosis is a critical cellular process for immune defense.
- Understanding the molecular mechanisms of phagocytosis, particularly membrane permeability changes, is essential.
- Pulmonary alveolar macrophages (PAMs) are key immune cells in the lung.
Purpose of the Study:
- To investigate elemental content changes in rat PAMs during phagocytosis of Pseudomonas aeruginosa.
- To explore the relationship between bacterial challenge and cellular membrane permeability.
- To utilize electron probe X-ray microanalysis (XRMA) for quantitative elemental analysis.
Main Methods:
- Cultured rat PAMs were challenged with P. aeruginosa.
- Samples were rapidly freeze-dried and sectioned at -100°C.
- Electron probe X-ray microanalysis (XRMA) was used to measure intracellular elemental concentrations (Na, Cl, K, Ca, Mg, P, S).
Main Results:
- Challenged PAMs showed a 4-fold increase in Na (p<0.001) and a 2-fold increase in Cl (p<0.001) compared to controls.
- Potassium levels decreased by 29% (p<0.001), and calcium increased 4-fold (p<0.05) in challenged PAMs.
- Elemental profiles of P. aeruginosa differed significantly from PAMs, with higher Na and Ca, and lower Cl and K.
Conclusions:
- Phagocytosis of P. aeruginosa induces significant intracellular elemental shifts in PAMs.
- These elemental changes suggest a stimulus-permeability response in the cell membranes during phagocytosis.
- XRMA is a valuable tool for studying cellular responses to bacterial challenge.