Cl-HCO3 exchange in choroid plexus: analysis by the DMO method for cell pH.

Area of Science:

• Physiology
• Biochemistry
• Neuroscience

Background:

• The choroid plexus (CP) is crucial for cerebrospinal fluid (CSF) production and maintaining brain homeostasis.
• Intracellular pH (pHi) and bicarbonate concentration ([HCO3]i) are vital parameters for CP function.
• Understanding ion transport mechanisms in the CP is essential for neurological research.

Purpose of the Study:

• To measure steady-state intracellular pH (pHi) and bicarbonate concentration ([HCO3]i) in adult rat choroid plexus.
• To investigate the influence of varying cerebrospinal fluid (CSF) bicarbonate and chloride concentrations on CP ion homeostasis.
• To elucidate the role of specific transporters and ion exchange in regulating CP intracellular environment.

Main Methods:

• Utilized [14C]DMO distribution to determine pHi and [HCO3]i in rat CP explants.
• Incubated CP in synthetic CSF with controlled PCO2, temperature, and ion concentrations.
• Administered pharmacological agents like acetazolamide, ouabain, and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid to probe transport mechanisms.

Main Results:

• Normal rat CP pHi (6.95) and bicarbonate accumulation threefold above electrochemical equilibrium were observed.
• [HCO3]i decreased with decreasing CSF [HCO3] and rose with increased PCO2 or reduced temperature.
• Inhibition of bicarbonate transport and anion exchange significantly altered [HCO3]i, rHCO3, and rCl.
• Chloride substitution with isethionate induced significant pHi alkalinization when CSF chloride was low.

Conclusions:

• Mammalian choroid plexus actively regulates intracellular bicarbonate and pH.
• Anion distribution ratios suggest heteroanion exchange mechanisms are operative in the CP.
• These findings contribute to understanding the complex ion transport dynamics in the cerebrospinal fluid-brain barrier.