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(1/13887) Energy depletion differently affects membrane transport and intracellular metabolism of riboflavin taken up by isolated rat enterocytes.

Isolated rat enterocytes, both normal and those de-energized with rotenone, were used to study the energy dependence of membrane and intracellular intestinal riboflavin transport in vitro. Membrane and intracellular transport were investigated by using short (3 min) and long (20 min) incubation times, respectively. For both types of cells and incubation times, [3H]-riboflavin uptake presented a saturable component prevailing at physiologic intraluminal concentrations. At 3 min incubation, saturable [3H]-riboflavin transport was apparently an energy-independent process with high affinity and low capacity. Values of the saturable component and its apparent constants, Km and Jmax, did not differ in normal and de-energized enterocytes. At 20 min incubation, saturable [3H]-riboflavin transport was a strictly energy-dependent process in which values of the saturable component were significantly greater in normal than in de-energized enterocytes. Km values did not differ in the two types of cells and were unmodified over 3 min, whereas in normal enterocytes, Jmax at 20 min [6.25 +/- 0.2 pmol/(mg protein. 20 min)] was significantly greater than at 3 min [2.67 +/- 0.33 pmol/(mg protein. 3 min)] and compared with de-energized enterocytes at 20 min [2.54 +/- 0.16 pmol/(mg protein. 20 min)]. Both membrane and intracellular events were inhibited by unlabeled riboflavin and analogs, which are good substrates for flavokinase, thus demonstrating the paramount role of this enzyme in riboflavin intestinal transport.  (+info)

(2/13887) Energy cost of sport rock climbing in elite performers.

OBJECTIVES: To assess oxygen uptake (VO2), blood lactate concentration ([La(b)]), and heart rate (HR) response during indoor and outdoor sport climbing. METHODS: Seven climbers aged 25 (SE 1) years, with a personal best ascent without preview or fall (on sight) ranging from 6b to 7a were assessed using an indoor vertical treadmill with artificial rock hand/foot holds and a discontinuous protocol with climbing velocity incremented until voluntary fatigue. On a separate occasion the subjects performed a 23.4 m outdoor rock climb graded 5c and taking 7 min 36 s (SE 33 s) to complete. Cardiorespiratory parameters were measured using a telemetry system and [La(b)] collected at rest and after climbing. RESULTS: Indoor climbing elicited a peak oxygen uptake (VO2climb-peak) and peak HR (HRpeak) of 43.8 (SE 2.2) ml/kg/min and 190 (SE 4) bpm, respectively and increased blood lactate concentration [La(b)] from 1.4 (0.1) to 10.2 (0.6) mmol/l (p < 0.05). During outdoor climbing VO2 and HR increased to about 75% and 83% of VO2climb-peak and HRpeak, respectively. [La(b)] increased from 1.3 (0.1) at rest to 4.5 mmol/l (p < 0.05) at 2 min 32 s (8 s) after completion of the climb. CONCLUSIONS: The results suggest that for elite climbers outdoor sport rock climbs of five to 10 minutes' duration and moderate difficulty require a significant portion of the VO2climb-peak. The higher HR and VO2 for outdoor climbing and the increased [La(b)] could be the result of repeated isometric contractions, particularly from the arm and forearm muscles.  (+info)

(3/13887) Cardiovascular and metabolic adaptations in horses competing in cross-country events.

The cardiovascular and metabolic response to two cross-country events (CC*: preliminary level and CC*** advanced level) were analysed in 8 male eventing horses (4 Anglo-Hunter and 4 Anglo-Arabian). This study focused on the establishment of the main metabolic pathways involved in the muscle energy resynthesis during the competitions. Heart rate (HR) was recorded throughout the CC events. Jugular venous blood samples were withdrawn before the warm-up period, immediately after the competitions and at 5 and 10 min in the recuperation period. The following haematological parameters were studied: red blood cells (RBC), packed cell volume (PCV), haemoglobin concentration (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), white blood cells (WBC), and number and percentages of lymphocytes (LYM) and granulocytes and monocytes (GRAN). One fraction of blood was centrifuged and, in plasma, lactate (LA), total plasma protein (TPP) and the rate of LA disappearance were determined. The competitions induced significant increases in RBC, Hb, PCV, MCV and TPP. Plasma LA response exceeded the anaerobic threshold of 4 mmol/l, reaching a maximum level of 13.3 mmol/l. HR ranged from 140 to more than 200 bpm, peaking at 230 bpm, revealing a limitation in the oxygen supply to the working muscles. It was concluded that muscle energy resynthesis during a CC event is provided both through oxidative processes and glycolysis with LA formation. Therefore, both stamina and power exercises are required for eventing horses.  (+info)

(4/13887) Energy cost of propulsion in standard and ultralight wheelchairs in people with spinal cord injuries.

BACKGROUND AND PURPOSE: Wheelchair- and subject-related factors influence the efficiency of wheelchair propulsion. The purpose of this study was to compare wheelchair propulsion in ultralight and standard wheelchairs in people with different levels of spinal cord injury. SUBJECTS: Seventy-four subjects (mean age=26.2 years, SD=7.14, range=17-50) with spinal cord injury resulting in motor loss (30 with tetraplegia and 44 with paraplegia) were studied. METHOD: Each subject propelled standard and ultralight wheelchairs around an outdoor track at self-selected speeds, while data were collected at 4 predetermined intervals. Speed, distance traveled, and oxygen cost (VO2 mL/kg/m) were compared by wheelchair, group, and over time, using a Bonferroni correction. RESULTS: In the ultralight wheelchair, speed and distance traveled were greater for both subjects with paraplegia and subjects with tetraplegia, whereas VO2 was less only for subjects with paraplegia. Subjects with paraplegia propelled faster and farther than did subjects with tetraplegia. CONCLUSION AND DISCUSSION: The ultralight wheelchair improved the efficiency of propulsion in the tested subjects. Subjects with tetraplegia, especially at the C6 level, are limited in their ability to propel a wheelchair.  (+info)

(5/13887) Nitric oxide inhibits cardiac energy production via inhibition of mitochondrial creatine kinase.

Nitric oxide biosynthesis in cardiac muscle leads to a decreased oxygen consumption and lower ATP synthesis. It is suggested that this effect of nitric oxide is mainly due to the inhibition of the mitochondrial respiratory chain enzyme, cytochrome c oxidase. However, this work demonstrates that nitric oxide is able to inhibit soluble mitochondrial creatine kinase (CK), mitochondrial CK bound in purified mitochondria, CK in situ in skinned fibres as well as the functional activity of mitochondrial CK in situ in skinned fibres. Since mitochondrial isoenzyme is functionally coupled to oxidative phosphorylation, its inhibition also leads to decreased sensitivity of mitochondrial respiration to ADP and thus decreases ATP synthesis and oxygen consumption under physiological ADP concentrations.  (+info)

(6/13887) Genetic evidence for ATP-dependent endoplasmic reticulum-to-Golgi apparatus trafficking of ceramide for sphingomyelin synthesis in Chinese hamster ovary cells.

LY-A strain is a Chinese hamster ovary cell mutant resistant to sphingomyelin (SM)-directed cytolysin and has a defect in de novo SM synthesis. Metabolic labeling experiments with radioactive serine, sphingosine, and choline showed that LY-A cells were defective in synthesis of SM from these precursors, but not syntheses of ceramide (Cer), glycosphingolipids, or phosphatidylcholine, indicating a specific defect in the conversion of Cer to SM in LY-A cells. In vitro experiments showed that the specific defect of SM formation in LY-A cells was not due to alterations in enzymatic activities responsible for SM synthesis or degradation. When cells were treated with brefeldin A, which causes fusion of the Golgi apparatus with the endoplasmic reticulum (ER), de novo SM synthesis in LY-A cells was restored to the wild-type level. Pulse-chase experiments with a fluorescent Cer analogue, N-(4,4-difluoro-5,7-dimethyl-4-bora-3a, 4a-diaza-s-indacene-3-pentanoyl)-D-erythro-sphingosine (C5-DMB-Cer), revealed that in wild-type cells C5-DMB-Cer was redistributed from intracellular membranes to the Golgi apparatus in an intracellular ATP-dependent manner, and that LY-A cells were defective in the energy-dependent redistribution of C5-DMB-Cer. Under ATP-depleted conditions, conversion of C5-DMB-Cer to C5-DMB-SM and of [3H]sphingosine to [3H]SM in wild-type cells decreased to the levels in LY-A cells, which were not affected by ATP depletion. ER-to-Golgi apparatus trafficking of glycosylphosphatidylinositol-anchored or membrane-spanning proteins in LY-A cells appeared to be normal. These results indicate that the predominant pathway of ER-to-Golgi apparatus trafficking of Cer for de novo SM synthesis is ATP dependent and that this pathway is almost completely impaired in LY-A cells. In addition, the specific defect of SM synthesis in LY-A cells suggests different pathways of Cer transport for glycosphingolipids versus SM synthesis.  (+info)

(7/13887) Expression of uncoupling protein-3 and mitochondrial activity in the transition from hypothyroid to hyperthyroid state in rat skeletal muscle.

We sought a correlation between rat skeletal muscle triiodothyronine (T3)-mediated regulation of uncoupling protein-3 (UCP3) expression and mitochondrial activity. UCP3 mRNA expression increased strongly during the hypothyroid-hyperthyroid transition. The rank order of mitochondrial State 3 and State 4 respiration rates was hypothyroid < euthyroid < hyperthyroid. The State 4 increase may have been due to the increased UCP3 expression, as the proton leak kinetic was stimulated in the hypothyroid-hyperthyroid transition and a good correlation exists between the State 4 and UCP3 mRNA level. As a significant proportion of an organism's resting oxygen consumption is dedicated to opposing the proton leak, skeletal muscle mitochondrial UCP3 may mediate part of T3's effect on energy metabolism.  (+info)

(8/13887) Reduced cytosolic acidification during exercise suggests defective glycolytic activity in skeletal muscle of patients with Becker muscular dystrophy. An in vivo 31P magnetic resonance spectroscopy study.

Becker muscular dystrophy is an X-linked disorder due to mutations in the dystrophin gene, resulting in reduced size and/or content of dystrophin. The functional role of this subsarcolemma protein and the biochemical mechanisms leading to muscle necrosis in Becker muscular dystrophy are still unknown. In particular, the role of a bioenergetic deficit is still controversial. In this study, we used 31p magnetic resonance spectroscopy (31p-MRS) to investigate skeletal muscle mitochondrial and glycolytic ATP production in vivo in 14 Becker muscular dystrophy patients. Skeletal muscle glycogenolytic ATP production, measured during the first minute of exercise, was similar in patients and controls. On the other hand, during later phases of exercise, skeletal muscle in Becker muscular dystrophy patients was less acidic than in controls, the cytosolic pH at the end of exercise being significantly higher in Becker muscular dystrophy patients. The rate of proton efflux from muscle fibres of Becker muscular dystrophy patients was similar to that of controls, pointing to a deficit in glycolytic lactate production as a cause of higher end-exercise cytosolic pH in patients. The maximum rate of mitochondrial ATP production was similar in muscle of Becker muscular dystrophy patients and controls. The results of this in vivo 31P-MRS study are consistent with reduced glucose availability in dystrophin-deficient muscles.  (+info)