We established quantitative histochemical assays for the enzymatic activity of succinate dehydrogenase and alpha-glycerol phosphate dehydrogenase for cat skeletal muscle. A computer-enhanced image analysis system was used to quantitate the histochemical enzyme-activity reaction products. We describe a series of experiments that verify the reliability and validity of the assays. Histochemically determined enzyme activities were linear with respect to tissue thickness and reaction time. Biochemically determined enzyme activities were also linear with respect to tissue thickness and incubation time. Consecutive tissue sections, assayed either histochemically or biochemically, were used to establish a linear regression equation that allowed quantitative histochemically determined reaction rates, measured in optical density per minute, to be calibrated as nanomoles per minute.
We evaluated the effect of endurance training (cycling 3 times per week for 12 weeks) on succinate dehydrogenase (SDH) activity in the subsarcolemmal (SS) and intermyofibrillar (IMF) regions of vastus lateralis muscle fibres in 7 individuals (4 females and 3 males). SDH activity of the SS region increased 9.4% and 12.8% in type I and II fibres, respectively (p < .05). SDH activity of the IMF region increased 4.7% and 6.7% in type I and II fibres, respectively (p < .05). This was less than the increase in the SS region (p < .05). No significant changes were observed in a control group (4 females and 3 males). These data suggest that mitochondria in the SS and IMF regions of human vastus lateralis muscle fibres are sensitive to endurance training. The greater response in the SS region suggests that the metabolic requirements of SS mitochondria were stressed to a greater extent than IMF mitochondria with endurance training.
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