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Cytosolic pH regulation in mouse macrophages. Proton extrusion by plasma-membrane-localized H(+)-ATPase
Abstract:
Recent evidence indicates that H+ extrusion in macrophages is in part accomplished by a H(+)-ATPase of vacuolar type. The presence and plasma-membrane localization of such a mechanism in adherent resident macrophages was verified by inhibition of H+ extrusion, monitored by changes in both cytosolic pH (pHi) and extracellular pH, with low concentrations of the H(+)-ATPase inhibitors N-ethylmaleimide and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole. The H(+)-ATPase was operative at physiological pHi levels, thus contributing to maintenance of steady-state pHi. It was further shown to be sensitive to the plasma-membrane potential, with hyperpolarization being strongly inhibitory. In addition, H+ extrusion mediated by the H(+)-ATPase and the generation and release of lactic acid caused acidification of the pericellular space and could enable secreted lysosomal hydrolases to act extracellularly.
Insights
Macrophages utilize vacuolar-type proton pumps (H(+)-ATPase) on their plasma membrane for acid extrusion, crucial for maintaining cellular pH and enabling extracellular enzyme activity.
Area of Science:
- Cell Biology
- Biochemistry
- Physiology
Background:
- Macrophages play a role in cellular pH regulation.
- Vacuolar-type proton pumps (H(+)-ATPase) are known to be involved in acid extrusion.
Purpose of the Study:
- To verify the presence and plasma membrane localization of H(+)-ATPase in adherent resident macrophages.
- To investigate the role of this H(+)-ATPase in maintaining cytosolic pH (pHi) and extracellular acidification.
Main Methods:
- Inhibition of H+ extrusion using specific H(+)-ATPase inhibitors (N-ethylmaleimide and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole).
- Monitoring of cytosolic pH (pHi) and extracellular pH changes.
- Assessment of sensitivity to plasma membrane potential.
Main Results:
- H(+)-ATPase activity was confirmed on the plasma membrane of macrophages.
- The pump functions at physiological pHi, contributing to steady-state pHi maintenance.
- H(+)-ATPase activity is inhibited by hyperpolarization of the plasma membrane.
Conclusions:
- Macrophages employ plasma membrane H(+)-ATPase for proton extrusion.
- This mechanism contributes to pericellular acidification, facilitating extracellular lysosomal hydrolase activity.
- Plasma membrane potential influences macrophage H(+)-ATPase function.