MITOCHONDRIAL ACTIVITIES OF RAT-HEART DURING AGING

Some analytical and functional parameters of rat heart mitochondria ha ve been investigated at six different periods of ageing from 2 to 26 m onths. The fatty acid composition of the mitochondrial membranes revea ls a percentage increase of polyunsaturated fatty acids (20:4 n-6, 22: 6 n-3) up to 12 months, followed by a decrease; however, fluorescence polarization of the membrane probe diphenylhexatriene is not changed, revealing that membrane fluidity is not significantly affected. No maj or change in ubiquinone-9 and in cytochrome content is apparent, indic ating that the relative ratio of the respiratory chain components is u nmodified. Nevertheless, significant changes in enzyme specific activi ties are detected: NADH cytochrome c reductase and cytochrome oxidase activities increase up to 12 months, then decrease at 18-26 months; ub iquinol cytochrome c reductase exhibits a peak at 18 months, followed by a decrease. All these activities follow a similar trend during the whole life span of the rat, even though the 'maximum' is different. No significant changes have been found in ATP synthase. Succinate-cytoch rome c reductase steadily increases over the whole life span. The resu lts, showing activity decreases in the respiratory enzymes having subu nits encoded by mitochondrial DNA, are compatible with the 'mitochondr ial' theory of ageing.