Titration of mitochondrial buffer by accumulated anions

Area of Science:

• Mitochondrial physiology
• Biochemistry
• Cell biology

Background:

• Mitochondria possess internal buffer systems crucial for maintaining pH homeostasis.
• Understanding these buffers is key to comprehending mitochondrial function and response to metabolic changes.

Purpose of the Study:

• To quantify the buffer power of intact and lysed rat liver mitochondria.
• To investigate the relationship between mitochondrial anion accumulation and buffer system properties.
• To explore the impact of permeant anions on intramitochondrial pH and buffer ionization.

Main Methods:

• Acidimetric titration of intact and Triton X-100 lysed rat liver mitochondria.
• Analysis of permeant anion uptake and distribution to determine intramitochondrial pH.
• Construction of titration curves based on internal pH and anion equivalents.

Main Results:

• Intact mitochondria show a buffer power of approximately 45 mEquiv/g between pH 7-8.
• Lysis with Triton X-100 increases the buffer power to 60 mEquiv/g.
• Mitochondrial anion accumulation influences internal pH and buffer ionization, consistent with Donnan equilibrium principles.
• A second method measuring buffer power via internal pH changes validated the acidimetric findings.

Conclusions:

• Rat liver mitochondria possess a significant buffer system, the capacity of which is revealed upon cell lysis.
• Mitochondrial anion transport and Donnan-like equilibria play a critical role in modulating the internal buffer system.
• The observed differences in buffer power between intact and lysed mitochondria align with theoretical predictions.