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Organellar clusters formed by mitochondrial‐rough endoplasmic reticulum associations: An ordered arrangement of mitochondria in hepatocytes
Author(s) -
Cascarano Joseph,
Chambers Patricia A.,
Schwartz Eileen,
Poorkaj Parvoneh,
Gondo Roy E.
Publication year - 1995
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.1840220323
Subject(s) - endoplasmic reticulum , mitochondrion , organelle , microsome , biology , hepatocyte , biochemistry , mitochondrial biogenesis , cytoplasm , microbiology and biotechnology , cytochrome c oxidase , chemistry , enzyme , in vitro
Our objective was to determine if mitochondrial‐rough endoplasmic reticulum (mt‐RER) associations provide for an ordered arrangement of mitochondria in the cell. If such an ordered arrangement exists, it might be manifested by grouping of mitochondria according to size and biochemical properties. Liver homogenate was subjected to rate zonal centrifugation for fractionating mitochondrial clusters. These clusters were then examined for morphological and biochemical characteristics. Scanning electron microscopy (SEM) showed that (1) mitochondria were held together in clusters by rough endoplasmic reticulum, (2) clusters consisted of mitochondria of comparable size, and (3) a 45‐fold difference in average mitochondrial volume existed between the organelles of the fastest and slowest sedimenting clusters. Transmission electron microscopy (TEM) affirmed that all of the organellar clusters examined were mitochondria associated with rough endoplasmic reticulum. Cytochrome oxidase and mitochondrial DNA were found to be proportional to mitochondrial volume, indicating that these components were synthesized in proportion to increases in volume. Conversely, succinic dehydrogenase and ornithine carbamoyl transferase were increased disproportionately (2.9‐fold and six‐fold, respectively) with increase in mitochondrial volume. It is evident from this biochemical heterogeneity that clusters composed of larger mitochondria differ functionally from clusters of smaller mitochondria. The size‐ordered arrangement suggests that this organization is in some way related to the biogenesis of hepatocyte mitochondria. It is also conjectured that the biochemical heterogeneity is a consequence of addition of selected proteins (e.g., succinic dehydrogenase and carbamoyl transferase) to mitochondria in a developmental process as they mature into larger organelles. (Hepatology 1995; 22:837–846.)