Interstitial carbonic anhydrase (CA) activity in brain is attributable to membrane-bound CA type IV

Area of Science:

• Neuroscience
• Biochemistry
• Physiology

Background:

• Extracellular carbonic anhydrase (CA) plays a role in regulating pH gradients.
• The specific contribution of membrane-bound CA type IV to interstitial pH regulation in the brain remains unclear.

Purpose of the Study:

• To investigate the role of membrane-bound carbonic anhydrase type IV in regulating interstitial pH (pH(o)) transients in the brain.
• To determine if CA IV is the primary regulator of pH(o) in the brain interstitium.

Main Methods:

• Rat hippocampal slices were treated with phosphatidylinositol-specific phospholipase C (PI-PLC) to cleave membrane-bound CA IV.
• Evoked alkaline pH(o) shifts were measured using pH microelectrodes in a recording chamber.
• Carbonic anhydrase activity in incubation fluid was analyzed using SDS treatment and Western blot.

Main Results:

• PI-PLC treatment significantly reduced the buffering capacity of brain slices against alkaline loads.
• The inhibitory effect of benzolamide on pH(o) shifts was diminished in PI-PLC-treated tissue, indicating CA washout.
• SDS-insensitive CA activity (characteristic of CA IV) was detected in the incubation fluid of PI-PLC-treated slices, while SDS-sensitive CA II was present in both treated and control slices.

Conclusions:

• Membrane-bound carbonic anhydrase type IV is the principal contributor to interstitial CA activity in the brain.
• CA IV plays a crucial role in regulating interstitial pH transients in the brain.
• Glial cell injury may release CA II, but CA IV is selectively released upon membrane cleavage.