Ultrastructural changes in atrial myocardium of the ageing rat.

Ageing changes in the fine structure of atrial myocardial cells were studied in rats ranging from 2-32 months in age. The most striking change observed was the increasingly frequent appearance, from about 6 months onwards, of helically aggregated strands containing filaments which in respects other than arrangement bore resemblance to thick myofilaments. Other ageing changes included the accumulation of dense bodies and various types of mitochondrial degradation.