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Increased ATP and creatine phosphate turnover in phagocytosing mouse peritoneal macrophages
Abstract:
Resident and thioglycollate-elicited macrophages maintained in culture for 24 h contain approximately 5 x 10(-16) and 12 x 10(-16) mol of ATP per cell, respectively. During particle ingestion, the levels of ATP in these cells did not change. However, the specific activity of ATP extracted from macrophages labeled with [32P]Pi during phagocytosis was 40% lower than ATP extracted from control cells. These results suggested that macrophages contain a high energy phosphate reservoir, in addition to the ATP pool(s). A search for such a reservoir led to the identification of creatine phosphate in both resident and thioglycollate-elicited macrophages at concentrations that are in 3- to 5-fold-molar excess over ATP. Creatine phosphate levels in phagocytosing resident macrophages decreased by 45%, while creatine phosphate levels in phagocytosing thioglycollate-elicited macrophages did not change. Creatine phosphate turnover was measured in macrophages prelabeled with [14C]creatine. Over 90% of the intracellular label was in the form of creatine phosphate. During phagocytosis, there was a 40% decrease in intracellular [14C]creatine phosphate in both resident and thioglycollate-elicited macrophages. These results indicate that creatine phosphate turns over more rapidly during phagocytosis and replenishes the ATP consumed.
Insights
Macrophages utilize creatine phosphate, a high-energy phosphate reservoir, to maintain adenosine triphosphate (ATP) levels during phagocytosis. This finding reveals a crucial energy buffering system in immune cells.
Area of Science:
- Cellular biology
- Immunology
- Biochemistry
Background:
- Macrophages are key immune cells involved in phagocytosis.
- Adenosine triphosphate (ATP) is the primary energy currency of cells.
- The energy demands of phagocytosis require efficient ATP regeneration.
Purpose of the Study:
- To investigate the energy metabolism of macrophages during phagocytosis.
- To identify potential high-energy phosphate reservoirs beyond ATP.
- To elucidate the role of creatine phosphate in macrophage energy homeostasis.
Main Methods:
- Culturing of resident and thioglycollate-elicited macrophages.
- Measurement of intracellular ATP levels and specific activity using [32P]Pi labeling.
- Quantification of creatine phosphate and its turnover using [14C]creatine labeling.
- Analysis of changes in ATP and creatine phosphate during phagocytosis.
Main Results:
- Intracellular ATP levels remained stable during phagocytosis, but ATP specific activity decreased by 40%.
- Creatine phosphate was identified as a high-energy phosphate reservoir, present in 3- to 5-fold molar excess over ATP.
- Phagocytosis led to a 45% decrease in creatine phosphate in resident macrophages and no change in thioglycollate-elicited macrophages.
- Creatine phosphate turnover increased significantly during phagocytosis, with a 40% decrease in intracellular [14C]creatine phosphate.
Conclusions:
- Macrophages possess a creatine phosphate energy buffering system to meet the demands of phagocytosis.
- Creatine phosphate rapidly replenishes consumed ATP during phagocytosis, maintaining cellular energy levels.
- The differential response of creatine phosphate levels suggests distinct metabolic adaptations in different macrophage populations.