AGE-DEPENDENT CHANGES OF ENZYME-ACTIVITIES IN THE DIFFERENT FIBER TYPES OF RAT EXTENSOR DIGITORUM LONGUS AND GASTROCNEMIUS-MUSCLES

The age-dependent change of metabolic profiles of SO (slow-oxidative), FOG (fast-oxidative glycolytic) and FG (fast-glycolytic) fibres of mu scules digitorum longus and musculus gastrocnemius of rat from 14 days to 370 days was measured cytophotometrically. Fibres were classified visually and using cytophotometrical data from staining reactions for myofibrillar adenosinetriphosphatase (ATPase), succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (alpha-GPDH) in the sa me fibre. The fibre type population as percentages was estimated at di fferent ages. The age-dependent change of enzyme activities was demons trated in each fibre type. SDH-heterogeneity of FOG-fibres and consequ ently an overlap with SO-fibres was detected. The alpha-GPDH/SDH-activ ity quotient allowed to distinguish SO-, FOG- and FG-fibres, and the a ge-dependent change of activity quotient characterized the change of m etabolic properties in the concerned fibre types. Whereas in gastrocne mius muscle the metabolic profile of FOG-fibres was similar to that of SO-fibres, in extensor digitorum longus muscle the metabolism of FOG- fibres was similar to that of FG-fibres. Between the two muscles diffe rences were also shown for the fibre type responsible for changes of e nzyme activities in the whole muscle, measured biochemically.