Bicarbonate-carbon dioxide buffer system: a determinant of the mitochondrial pH gradient

Area of Science:

• Biochemistry
• Cell Biology
• Physiology

Background:

• Mitochondria maintain a pH gradient across their inner membrane, crucial for ATP synthesis.
• The bicarbonate-carbon dioxide buffer system is a primary physiological buffer.
• Understanding its role in mitochondrial pH regulation is vital for cellular function.

Purpose of the Study:

• To investigate the influence of the bicarbonate-carbon dioxide buffer system on the mitochondrial inner membrane pH gradient (delta pH).
• To explore the role of phosphate and its interaction with the bicarbonate buffer system in modulating delta pH.
• To elucidate the mechanisms by which the bicarbonate buffer system affects mitochondrial pH.

Main Methods:

• Mitochondria isolated from rabbit renal cortex, liver, and heart were used.
• Measurement of pH gradient (delta pH) across the inner mitochondrial membrane under varying buffer conditions.
• Pharmacological inhibition of the phosphate-hydroxyl carrier using N-ethylmaleimide.

Main Results:

• The bicarbonate buffer system significantly influenced the mitochondrial delta pH.
• Phosphate concentration had a minor effect on delta delta pH with bicarbonate buffer.
• Inhibition of the phosphate-hydroxyl carrier altered delta delta pH differently depending on bicarbonate presence.

Conclusions:

• The bicarbonate buffer system affects mitochondrial delta pH, potentially via CO2 permeability or an active bicarbonate carrier.
• This system may regulate substrate metabolism in response to acid-base changes in kidney cells.
• It can help stabilize matrix pH during cytoplasmic pH fluctuations in various organs.