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ABSTRACT: Previously, we showed that the decrease in force output during continuous isometric contractions in rat skeletal muscle was related to an increase in the concentration of IMP. In this paper we report on additional experiments in which the effect of IMP on the Mg(2+)-stimulated acto-myosin-ATPase activity of isolated actin and myosin is measured at 35 degrees C. The results show that 1) the binding of actin to myosin is co-operative (Hill coefficient = 3.82); 2) in the presence of IMP or AMP the Mg(2+)-stimulated acto-myosin-ATPase activity is inhibited up to 60% at 10 mM; 3) in the presence of IMP or AMP not only the Mg(2+)-stimulated acto-myosin-ATPase activity decreases, but also K(50). From these results we conclude that IMP and AMP may be considered as uncompetitive inhibitors. Our results suggest that IMP and AMP can prevent an 'energy crisis' during exhaustive exercise of short duration by down-regulating the contractile machinery.
Archives of Physiology and Biochemistry 11/2001; 109(4):316-22.
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ABSTRACT: A quick, cheap, and accurate method for the determination of ammonia in air is described. Ammonia and water vapor are trapped simultaneously in a gas sampling tube cooled in liquid nitrogen. Subsequently ammonia is derivatized with o-phthaldialdehyde and determined using fluorescence detection. The detection limit of ammonia in a gaseous sample is about 1 nmol per liter of gas. The recovery, using a calibration gas of 6.00 ppm ammonia in nitrogen, is 102.9 +/- 6.4%. Examples are presented in which this method is used for the determination of ammonia in environmental air and in expired air during exhaustive exercise of a human subject. It is suggested that this method can be used for the determination of volatile ammonia and other compounds in air during environmental and biological monitoring and in research.
Analytical Biochemistry 10/2001; 296(2):225-31. · 3.00 Impact Factor
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Journal of Chromatography 12/1989; 496(2):441-9. · 4.53 Impact Factor
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Journal of Chromatography 05/1989; 489(2):419-24. · 4.53 Impact Factor
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ABSTRACT: Changes in isometric force, power output and relaxation rate have been measured during repetitive tetanic contractions in 2 groups of rats of different ages. During the first 5 contractions there were no differences between a young and mature group. In contrast to isometric force production, which decreased about 3% per contraction, power output initially increased to 108% of the power output in the first contraction. A greater reduction in power output and relaxation rate after the 5th contraction indicated a greater reduction of the cross-bridge cycling rate in the younger rats. ATP, phosphocreatine and lactate concentrations after the last contraction were not different between the age-groups. In contrast IMP production, which has been suggested may play a regulatory role during fatigue was twice as high in the young rats. Judged by isometric force production there is no age-related difference in fatiguability. However, profound differences were observed in power output, which indicates that quantification of fatigue as a loss of isometric force may be seriously misleading when considering the functional status of the muscle for normal dynamic contractions.
Pflügers Archiv - European Journal of Physiology 11/1988; 412(6):665-7. · 4.46 Impact Factor
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ABSTRACT: The time course was examined of the energy-rich phosphate usage and exerted isometric tetanic force in electrically stimulated rat quadriceps muscle. The maximal rate of energy-rich phosphate usage was calculated from the changes in the intramuscular concentrations of phosphocreatine, lactate, ATP and inosine monophosphate (IMP) and was somewhat higher than those calculated on the basis of exercise in vivo. The IMP concentration increased directly from the onset of the contraction until after about 11 s it remained constant. The increase in the IMP concentration coincided with a decrease in the ATP concentration. The relationship between mechanical output and energy usage was examined in two ways (i) by calculating the ratio time integral of the force (FTI) and the total energy-rich usage (Ptot) and (ii) by calculating the ratio Force (Ft) to the energy flux (dPtot/dt) at a certain time t. Whereas the ratio FTI/Ptot showed a hyperbolic relationship, the ratio Ft/(dPtot/dt) showed a parabolic relationship. From the latter finding and from the results described in the literature it is concluded that the ratio mechanical output/energy-rich phosphate usage depends on the conditions under which exercise is carried out. Recovery under aerobic conditions from a maximal tetanic isometric contraction sustained for 15 s was slow compared to results of experiments in vivo.
Pflügers Archiv - European Journal of Physiology 08/1988; 412(1-2):121-7. · 4.46 Impact Factor
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ABSTRACT: The effect of muscle dimensions on economy (force-time integral divided by the amount of energy utilized) was investigated in male rats (body mass range 95-490 g), anaesthetized with pentobarbital. The medial gastrocnemius muscle in situ performed 6 maximal isometric contractions of 350 ms duration (1.s-1) at twitch optimum length at 35 degrees C. The areas under the 6 time-force curves were added to obtain force-time integral of the experiment. Differences of concentrations of ATP, phosphocreatine and lactate between experimental and contralateral (resting) muscles were used to calculate high-energy phosphate consumption due to stimulation. Muscle mass and cross-sectional area increased (approximately +400% and +300%, respectively) over the rat body mass range studied. Muscle length and length of the most distal fibre bundle increased by approximately 17 mm and 4 mm, respectively. Force-time integral (N.s) increased proportional to cross-sectional area whereas high-energy phosphate consumption (mumoles) increased proportional to muscle mass. The relative fraction of the total energy consumption utilized for force-independent processes was independent of rat body mass. The economy of the actomyosin system was unaffected during growth, whereas economy of the whole muscle decreased during growth by approximately 30% (p less than 0.001). The effect of muscle dimensions on economy is discussed with respect to human endurance capacity measured by voluntary isometric contractions.
European Journal of Applied Physiology and Occupational Physiology 02/1988; 57(1):64-9.
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ABSTRACT: IMP production in and force exerted by rat quadriceps muscle in situ during various types of exercise were examined in relation to age. During continuous isometric exercise with constant stimulation time, the amount of IMP was linearly and inversely related to the age of the animals; a higher IMP concentration was found in intermittent isometric and dynamic exercise. No relationship was found between the total AMP deaminase activity and age. Exercise influenced neither the total activity nor the activity in the soluble fraction. From the results it is concluded that: the IMP concentration is linearly related to the free intracellular ATP4-/ADP3- ratio and the free AMP2- concentration; older animals are better able to maintain a high intramuscular ATP4-/ADP3- ratio and a low AMP2- concentration; IMP is produced in particular under conditions when the muscle has to work under extreme stress. IMP possibly exerts a feed-back control on the contraction system.
Biochemical Journal 12/1986; 239(3):751-5. · 4.90 Impact Factor
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ABSTRACT: For rat medial gastrocnemius muscle economy (i.e. the ratio of time integral of force and total energy-rich phosphate consumption) was calculated. Muscles in situ at 35 degrees C were stimulated to perform either one continuous or several repetitive isometric contractions at one muscle length in the range from 70% to 130% of optimum muscle length for force generation. Whereas during one continuous contraction economy increased, no differences in economy were found between 6, 12 or 18 successive contractions. Economy during intermittent exercise was always lower than during continuous exercise. The difference in economy is a result of different rates of metabolism, whereas no difference was found for force generation. Economy was highest at optimum muscle length for force generation and decreased at muscle lengths smaller as well as greater than optimum muscle length. Force-dependent energy consumption was calculated by subtracting the force-independent part (obtained by extrapolation) from total energy consumption. The calculated force produced per mumol force-dependent energy-rich phosphate consumption was similar in muscles stretched beyond optimum length. In contrast, a decreasing amount of force per mumol force-dependent energy-rich phosphate consumption was observed at lengths smaller than optimum length.
Pflügers Archiv - European Journal of Physiology 11/1986; 407(4):445-50. · 4.46 Impact Factor
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ABSTRACT: Improvement of muscle performance by 20%-50% in man at a submaximal work load after administration of potassium and magnesium salts of aspartic acid (K + Mg Asp) has been reported in the literature. Administration of K + Mg Asp has been reported to affect force production and energy metabolism in short-term activities of electrical stimulated animal muscles. The present study examined the possible effects of K + Mg Asp on: energy metabolism and force production of electrically stimulated rat quadriceps muscle and endurance time of a submaximal static force of voluntary contracting human muscles. In rat muscles metabolic parameters such as ATP, phosphocreatine, lactate, and L-aspartate were not influenced by oral administration of K + Mg Asp. Force parameters of rat quadriceps muscles were not enhanced after administration of K + Mg Asp. In human volunteers neither the exerted force nor the endurance time increased after oral administration of K + Mg Asp. An effect of K + Mg Asp on muscle metabolism by stimulation of the purine nucleotide cycle was not found. Improvement of muscle performance by 20%-50%, as reported for long-term activity, was not observed for short-term intensive activity.
International Journal of Sports Medicine 03/1985; 6(1):44-9. · 2.43 Impact Factor
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ABSTRACT: The effect of intensive interval training on the maximal anaerobic power of the rat quadriceps muscle was investigated. The anaerobic energy production was estimated from the changes in the concentrations of phosphocreatine, adenine nucleotides, inosine monophosphate and lactate in freeze-clamped muscle tissue after electrical stimulation for 2-30 s. The results showed that the maximal running speed of rats tested increased by 24%, the maximal force exerted increased by 13%, and the succinate dehydrogenase activity by 48%, while the adenylate kinase activity was the same before and after training. No difference could be observed between the maximal anaerobic power of the quadriceps muscles of trained and sedentary animals. It seems that trained muscles may be able to work with a higher degree of economy than untrained muscles.
Journal of Sports Sciences 02/1985; 3(2):139-50. · 1.93 Impact Factor
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ABSTRACT: A quick, cheap, and accurate method for the determination of ammonia in air is described. Ammonia and water vapor are trapped simultaneously in a gas sampling tube cooled in liquid nitrogen. Subsequently ammonia is derivatized with o-phthaldialdehyde and determined using fluorescence detection. The detection limit of ammonia in a gaseous sample is about 1 nmol per liter of gas. The recovery, using a calibration gas of 6.00 ppm ammonia in nitrogen, is 102.9 ± 6.4%. Examples are presented in which this method is used for the determination of ammonia in environmental air and in expired air during exhaustive exercise of a human subject. It is suggested that this method can be used for the determination of volatile ammonia and other compounds in air during environmental and biological monitoring and in research.
Analytical Biochemistry.
