Inducibility of NADP-specific isocitrate dehydrogenase with endurance training in skeletal muscle

NADP(+)-specific isocitrate dehydrogenase (ICDH-NADP: EC 1 x 1 x 1 x 42) is primarily a mitochondrial matrix enzyme in both mammalian skeletal muscle and heart and has markedly higher activity levels than the NAD(+)-specific isozyme. To date, it is unknown whether ICDH-NADP activity is inducible with in vivo exercise training in locomotor or respiratory skeletal muscle. Therefore, the purpose of this investigation was to quantify alterations in ICDH-NADP activity in respiratory muscles (costal and crural diaphragm) and locomotor muscles (medial gastrocnemius, plantaris and soleus) following 8 weeks of treadmill endurance training. Ten of the animals had been assigned randomly to an exercise group (TR) and had completed 8 weeks of progressive (5 days week-1: 45 min day-1) treadmill endurance training while the remaining 10 animals comprised a sedentary control (C). Mean ICDH-NADP activities in Tr were significantly higher (P < 0.05) when compared with C in the medial gastrocnemius (61.3%), plantaris (42.9%) soleus (21.4%). Mean costal diaphragm ICDH-NADP activity noted in trained animals when compared to the sedentary control group was not significantly higher (10.8% greater for TR; P = 0.14). No mean differences (P = 0.58) were noted in the crural diaphragm. The results indicate that ICDH-NADP is inducible with endurance training in locomotor skeletal muscle. A coefficient of determination of 0.624 (i.e. 62.4% of the variance could be explained) for ICDH-NADP was calculated, with the oxidative enzyme marker succinate dehydrogenase (P < 0.05) indicating a positive, moderate relationship.(ABSTRACT TRUNCATED AT 250 WORDS)