Cytochemical estimation of COX activity and morphometric measurement of mitochondrial ultrastructure were carried out in organelles from adult and old rats. Although no age-related difference was found in cytochemical precipitate (CPA) and mitochondrial area (MA), the ratio CPA:MA (R) decreased by 25.7% in aging. R was the same in oversized mitochondria, but in smaller organelles it was significantly decreased during aging. R reports on the functional mitochondrial surface involved in energy providing mechanisms; thus, by revealing age-related differences, these data suggest that the COX preferential cytochemistry associated with morphometry may serve as a reliable and sensitive mitochondrial morphofunctional check-up procedure.
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