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Mitochondrial flocculent densities in ischemia. Digestion experiments
Abstract:
Flocculent densities appear in the mitochondrial matrix during ischemic damage. These densities were examined in kidneys after 2 hours of autolysis. The samples were embedded in water-miscible glycol methacrylate (GMA). Ultrathin sections on copper grids were digested with pronase, trypsin, ribonuclease T1, various phospholipases (A2, C, D), lipase, and desoxyribonuclease I. For statistical analysis the mean number (+/- SD) of densities per mitochondrion was determined in tubular epithelial cells. A statistically significant (p less than 0.001) decrease in the number of densities was apparent after treatment with pronase (75.5%) of the densities digested completely) and with trypsin (43.3% of the densities digested completely). Digestion with other enzymes did not significantly decrease the number of densities. This study provides quantitative support for the hypothesis that flocculent densities are composed of proteins, most probably mitochondrial membrane proteins or matrix proteins. The results do not support the hypothesis that RNA, neutral lipids, phospholipids or DNA are major constituents of these structures.
Insights
Flocculent densities in mitochondria, observed during ischemic damage, were found to be primarily composed of proteins. Enzymatic digestion experiments confirmed proteins as the main component, not RNA, lipids, or DNA.
Area of Science:
- Cell Biology
- Pathology
- Biochemistry
Background:
- Flocculent densities are observed in the mitochondrial matrix during ischemic damage.
- Understanding the composition of these densities is crucial for comprehending cellular injury mechanisms.
Purpose of the Study:
- To investigate the biochemical composition of flocculent densities in kidney mitochondria following ischemic damage.
- To quantitatively assess the role of proteins, RNA, lipids, and DNA in forming these mitochondrial structures.
Main Methods:
- Kidney samples underwent 2 hours of autolysis and were embedded in glycol methacrylate (GMA).
- Ultrathin sections were subjected to enzymatic digestion using pronase, trypsin, ribonuclease T1, phospholipases, lipase, and desoxyribonuclease I.
- The number of densities per mitochondrion in tubular epithelial cells was statistically analyzed after digestion.
Main Results:
- Pronase digestion significantly reduced densities by 75.5%, and trypsin by 43.3%.
- Digestion with other enzymes did not yield significant reductions in density numbers.
- These findings provide quantitative evidence for the proteinaceous nature of flocculent densities.
Conclusions:
- Flocculent densities are predominantly composed of proteins, likely mitochondrial membrane or matrix proteins.
- The results do not support the hypothesis that RNA, neutral lipids, phospholipids, or DNA are major constituents.
- This study offers quantitative support for a protein-based composition of mitochondrial flocculent densities.
