Direct counting and sizing of mitochondria in solution.

Area of Science:

• Cell Biology
• Biophysics
• Biochemistry

Background:

• Mitochondria are vital organelles involved in cellular energy production.
• Accurate sizing and counting of mitochondria are essential for understanding cellular function and disease.
• Existing methods for mitochondrial analysis have limitations in speed and accuracy.

Purpose of the Study:

• To develop and validate a resistive particle counting technique for precise mitochondrial sizing and enumeration.
• To compare the results obtained from resistive particle counting with established microscopy techniques.
• To investigate the influence of mitochondrial integrity and contaminants on size distribution measurements.

Main Methods:

• Utilized resistive particle counting with a 30-micrometer aperture for mitochondrial analysis.
• Determined mean mitochondrial volume and diameter in rat liver, heart, and kidney cortex.
• Calculated particle numbers per milligram of mitochondrial protein and per gram of rat liver.
• Assessed the impact of mitochondrial fragility and contaminating organelles on size distribution.

Main Results:

• Resistive particle counting achieved a detection limit of 0.48 micrometer diameter or 0.056 cubic micrometer particle volume.
• Mean volumes for rat liver, heart, and kidney cortex mitochondria were 0.42, 0.60, and 0.23 cubic micrometer, respectively.
• Mitochondrial counts per milligram of protein and per gram of liver were 4.3 x 10^3 and 11 x 10^10, respectively.
• Results showed good agreement with light and electron microscopy, with discrepancies within 15% for kidney mitochondria.

Conclusions:

• Resistive particle counting is a reliable method for accurate mitochondrial sizing and counting in solution.
• The technique is applicable to various biological states and can be used for rapid swelling studies.
• Mitochondrial constituents like DNA, RNA, and cytochromes remain constant per particle during growth, supporting biogenesis hypotheses.