Noriaki Fujitsuka

Induction of nuclear respiratory factor-1 expression by an acute bout of exercise in rat muscle.

Nuclear respiratory factor 1 (NRF-1) is a regulatory factor of nuclear genes for respiratory subunits and for components of the mitochondrial transcription and replication machinery. This study investigated the effects of an acute bout of aerobic exercise on the postexercise expression of mRNA for NRF-1 and RNA moiety of endonuclease for mitochondrial RNA processing (MRP-RNA) in soleus muscle of 5 days-trained and untrained rats. In the trained group, rats were run on a motor-driven treadmill at a speed of 25 m/min for 90 min/day for 5 days. On the final day, rats were run by the same procedures and were sacrificed at various postexercise time points (0.5, 3, 6, and 24 h). The basal level of cytochrome oxidase activity was increased by the training, which was associated with the increase in the expression of mRNAs for subunit VIc and III of the enzyme. The NRF-1 mRNA expression was transiently increased by approximately 35% at the time point of 6 h after exercise, although the basal level of the expression was not altered by training. A similar transient increase (approximately 50%) in NRF-1 expression by the acute bout of exercise was also observed in untrained rats. In contrast to the NRF-1 expression, the basal level of MRP-RNA abundance was not altered by 5 days training and was not affected by the single exercise bout in either 5 days-trained or untrained rats. These results suggest that the postexercise increase in NRF-1 mRNA expression in rat skeletal muscle may be an early response to endurance exercise for an enhancement of the mitochondrial oxidative capacity.

Peak blood lactate after short periods of maximal treadmill running

SummaryBlood lactate was determined in 19 untrained subjects after maximal treadmill exercise lasting for about 1 min. It was found that blood lactate increases after exercise, reaching a maximum level 6–9 min after the cessation of exercise, and the average time for the appearance of the peak blood lactate concentration was 7.65 min. Peak blood lactate concentration at 7.65 min (CLA7.65), which was calculated by substituting t (7.65) into the equation for the lactate recovery curve for each subject, agreed well with the observed peak blood lactate concentration (r=0.98, p<0.001). In addition, correlations of r=−0.65, r=−0.78, r=−0.79 were found between CLA7.65 and the running times of 100 m, 200 m, and 400 m sprints, respectively. These results suggest that CLA7.65 may be used as a valid indicator of anaerobic work capacity in man.

Regulation of valine catabolism in canine tissues: tissue distributions of branched-chain aminotransferase and 2-oxo acid dehydrogenase complex, methacrylyl-CoA hydratase and 3-hydroxyisobutyryl-CoA hydrolase

To clarify the valine catabolism, the activities of principal enzymes in its catabolic pathway, branched-chain aminotransferase, branched-chain 2-oxo acid dehydrogenase complex, methacrylyl-CoA hydratase and 3-hydroxyisobutyryl-CoA hydrolase, were measured using canine tissues. After killing of beagle dogs, tissues (liver, pancreas, kidney, heart, skeletal muscle and mucosae of digestive organs such as stomach, small intestine and colon) were removed and immediately frozen. Branched-chain aminotransferase activity in liver was the lowest among the tissues measured. In contrast, the activities of branched-chain 2-oxo acid dehydrogenase complex in liver as well as in kidney were relatively high and the enzyme complex activities were markedly low in small intestine and skeletal muscle. The activities of methacrylyl-CoA hydratase and 3-hydroxyisobutyryl-CoA hydrolase were relatively high in all tissues, suggesting that a cytotoxic intermediate, methacrylyl-CoA, is immediately degraded to non-toxic compounds, 3-hydroxyisobutyrate and free CoA. These findings suggest that the consumption of branched-chain amino acids in the absorption site (small intestine) is suppressed in order to supply them to the whole body, in particular to skeletal muscle and that skeletal muscle might act as a storage of gluconeogenic amino acids. The high capacity to dispose methacrylyl-CoA produced in the valine catabolism is suggested to play an important role in protecting cells against the toxic effects of methacrylyl-CoA.

Branched-chain 2-oxo acid dehydrogenase complex activation by tetanic contractions in rat skeletal muscle

Branched-chain 2-oxo acid dehydrogenase complex in rat skeletal muscle was activated by muscle contractions elicited by electrical stimulation. This activation was attributed to dephosphorylation of the phosphorylated enzyme complex, and the total enzyme activity was not altered by muscle contractions. The activation of the enzyme complex occurred in the muscle of the electrically stimulated leg, but not in the muscle of the non-stimulated (control) leg, indicating that blood components are not involved in the mechanism of the enzyme activation in the muscle. Adenine nucleotides, branched-chain amino and 2-oxo acids and lactate in the muscle were determined as possible factors modulating the enzyme complex activity through inhibition of branched-chain 2-oxo acid dehydrogenase kinase activity. The profile of enzyme activation induced by muscle contractions was different from the alteration of the adenine nucleotide concentrations but was similar to the alteration of the concentrations of branched-chain amino and 2-oxo acids in the muscle. The lactate concentration in the stimulated muscle was elevated 3-5-fold during the contractions, indicating intracellular acidification. Previous studies have shown that the 2-oxo acid derived from leucine is a potent inhibitor of the kinase. These results suggest that intracellular branched-chain 2-oxo acids increased by muscle contractions accumulate in the mitochondria due to exercise-induced acidification of the muscle cell, resulting in activation of branched-chain 2-oxo acid dehydrogenase complex by inhibition of the kinase.

Ventilatory response to hypercapnia in sprint and long-distance swimmers

SummaryVentilatory response lines to carbon dioxide at rest were determined by the rebreathing method in 10 untrained subjects, 17 sprint swimmers, and 11 long-distance swimmers. It was found that the mean slope of the ventilatory response line of the swimmer was lower than that of the untrained group, and the mean slope of the long distance swimmer was lower as compared with the sprint swimmer, though these differences were statistically not significant. The differences in the hypercapnic drive between untrained subjects and swimmers obtained here is discussed in connection with their maximum oxygen uptake.

Insulin activation of pyruvate dehydrogenase complex is enhanced by exercise training

We studied the effects of exercise training on the activity of the pyruvate dehydrogenase (PDH) complex in rat gastrocnemius muscle (experiment 1) and the response of the complex to glucose and insulin infusion (euglycemic clamp) in trained and sedentary rats (experiment 2). In experiment 1, half of the rats were randomly allocated as sedentary animals and the other half were trained by voluntary running exercise for 8 weeks. The total activity of the PDH complex was not affected by exercise training, and the activity state (proportion of the active form) of the PDH complex was decreased from 15.0%+/-2.4% to 7.5%+/-1.1% by exercise training. The activity of 3-hydroxyacyl-coenzyme A (CoA) dehydrogenase ([3-HADH] an enzyme in beta-oxidation) was significantly higher in trained versus sedentary rats. In experiment 2, sedentary and trained rats were starved for 24 hours before performing the euglycemic clamp. Glucose and insulin infusion was performed by a euglycemic clamp (insulin infusion rate, 6 mU/kg/min) for 90 minutes. The PDH complex was inactivated to less than 1% in both sedentary and trained rats after 24 hours of starvation. The glucose infusion rate (GIR) during the euglycemic clamp was higher in trained versus sedentary rats. The euglycemic clamp resulted in activation of the PDH complex in both sedentary and trained rats, but the response of the PDH complex to the euglycemic clamp was significantly higher in trained rats (5.8%+/-0.5%) than in sedentary rats (2.9%+/-0.5%). These results suggest that exercise training promotes fatty acid oxidation in association with suppression of glucose oxidation in skeletal muscle under resting conditions, but increases the rate of carbohydrate oxidation when glucose flux into muscle cells is stimulated by insulin.

GK(Ca)-dependent cyclic potential changes in the sensory nerve terminal of frog muscle spindle

Spontaneous cyclic hyperpolarizations along the sensory nerve terminal of frog muscle spindles were observed during the application of 1-9 nA depolarizing currents across an air-gap on which the axon was bridged. An increase in the current intensity increased the amplitude and duration of the cyclic changes. Upon subthreshold depolarization, single or repetitive hyperpolarizations could be elicited after a brief electric pulse or during stretch of the receptors, respectively. The threshold was decreased in higher Ca2+, Sr2+ or Ba2+ solutions. The cyclic changes were reversibly blocked by K+- or Ca2+-blockers and quinine. These results suggest that the changes are due to GK(Ca). The site of origin of the changes was at the branching node in the capsule, as confirmed by the following results: (1) the cyclic changes were abolished upon inactivating the node by UV-irradiation; (2) in normal Ringers solution, the rate of afferent impulses, which reflects the membrane potential at the encoding site along the non-myelinated filaments, was unmodified by the cyclic changes and was independent of the intensity of the polarizing currents within a certain range; however, it was sensitively dependent on this intensity after treatment with K+-blockers; (3) the amplitude of the impulses reaching the branching node was attenuated during the cyclic changes, but not after GK-blockade.

The abundance of mRNAs for pyruvate dehydrogenase kinase isoenzymes in brain regions of young and aged rats.

The abundance of mRNAs for pyruvate dehydrogenase kinase (PDK) isoenzymes in four brain regions of young (10 wk) and aged (50 wk) rats was investigated by reverse transcription-polymerase chain reaction (RT-PCR). The mRNAs for PDK1, 2, and 4 were detected in all the regions examined. The level of PDK2 mRNA was the most abundant among the isoenzymes in all the brain regions when judged from the PCR cycles. The level of PDK1 mRNA was relatively high in cerebellum and cerebral cortex compared to medulla oblongata and hippocampus. Aging decreased the levels of mRNAs for PDK1 and 2 in cerebellum and increased the PDK2 mRNA in hippocampus and cerebral cortex. The level of PDK4 mRNA was not affected by aging. These results provide the first evidence suggesting that there is the regional difference in the abundance of mRNAs for PDK isoenzymes in rat brain and that the levels of mRNAs for the isoenzymes were affected by aging.

Effects of aging on the activities of pyruvate dehydrogenase complex and its kinase in rat heart.

Effects of aging on the activities of heart pyruvate dehydrogenase complex and pyruvate dehydrogenase kinase were examined using 7, 35 and 60 wk old rats. Aging did not affect the total activity of pyruvate dehydrogenase complex but decreased the activity state (percentage of active form) of the complex in rats under the fed condition (52%, 36% and 26% for 7, 35 and 60 wk old rats, respectively). This decrease in the complex activity with aging was suggested to be associated with an age-related decrease in the blood glucose disposal. Starvation for 24 h decreased the activity state to less than 3% in all of the age groups. The activity of pyruvate dehydrogenase kinase associated with the complex was not related to the alteration in the activity state of the complex; the kinase activity was slightly lower in 60 wk old rats than in the younger rats under the fed condition and activation of the kinase by starvation was greater in the younger rats. The mechanism for the decrease in activity of pyruvate dehydrogenase complex was discussed on the basis of glucose and fatty acid utilization of heart muscle cells.

Activities of liver pyruvate dehydrogenase complex and 3-hydroxyacyl-CoA dehydrogenase in sand rat (Psammomys obesus)

The sand rat (Psammomys obesus) is an animal model for non-insulin dependent diabetes mellitus, which is induced by a regular chow diet. The total activity of liver pyruvate dehydrogenase complex in the sand rats under normoglycemic and normoinsulinemic conditions was one half as high as that in the albino rats, but the activity of liver 3-hydroxyacyl-CoA dehydrogenase was more than 4 times greater in the former than in the latter, suggesting a low capacity for glucose oxidation and a high capacity for fatty acid oxidation in the sand rats. These metabolic conditions may be related to the predisposition of the animals towards diabetes. Diet-induced diabetes in the sand rats resulted in decreasing the active form of liver pyruvate dehydrogenase complex and in increasing the activity of liver 3-hydroxyacyl-CoA dehydrogenase, suggesting that the diabetic conditions further suppress glucose oxidation and promote fatty acid oxidation.