Astrocytes fail to regulate intracellular pH at moderately reduced extracellular pH

Area of Science:

• Cell biology
• Physiology
• Biochemistry

Background:

• Intracellular pH (pHi) regulation is crucial for astrocyte function.
• Astrocytes employ various mechanisms to maintain pHi homeostasis.
• The role of extracellular pH (pHe) in pHi regulation requires further elucidation.

Purpose of the Study:

• To investigate the regulation of pHi in astrocytes loaded with 2'-7'-bis (carboxyethyl-)-5,6-carboxyfluorescein (BCECF).
• To determine the influence of extracellular pH (pHe) on astrocyte pHi regulation.
• To challenge the established model of H+ regulatory sites.

Main Methods:

• Microspectrofluorometry was employed to measure pHi in BCECF-loaded astrocytes.
• Acid transients were induced using an NH4+ prepulse.
• The effects of Na+ removal, amiloride, and varying pHe on pHi regulation were assessed.

Main Results:

• Astrocytes demonstrated rapid regulation of acid transients.
• This regulation was inhibited by Na+ removal or amiloride.
• Lowering pHe significantly inhibited pHi regulation, with pHi changing in parallel to pHe.
• An efficient H+ extrusion mechanism was identified.

Conclusions:

• Astrocyte pHi regulation is dependent on stable extracellular pH (pHe).
• The findings question the existence of an internal H+ regulatory site on the exchanger that maintains a constant pHi.
• Astrocytes require constant pHe for effective pHi homeostasis despite possessing efficient H+ extrusion.