The movement of amino acids between blood and skeletal muscle in the rat

Baños, Guadalupe; Daniel, P. M.; Moorhouse, S.; Pratt, O. E.

doi:10.1113/jphysiol.1973.sp010397

Cited by 64 publications

(29 citation statements)

References 17 publications

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“…The uptake of amino acids by isolated microvessels in suspension is anatomically equivalent to the passage of substances from the brain into the blood whereas the in situ injection technique is from the blood into the brain. The finding that the apparent Km values for the transport of large neutral amino acids are similar on both sides of the microvascular wall suggests that the transport mechanism is not asymmetric (25)(26)(27)(28) (29). The similarities between the sodium and energy independent large neutral amino acid carrier system and the L system proposed by Christensen et al (30) have been noted (18).…”

Section: Discussionmentioning

confidence: 88%

“…From morphological studies, the barrier to the diffusion of molecules into the brain and retina from the blood is believed to reside at the level of the microvascular endothelium with its tight junctions (1,4). Studies into the nature of the selective entry of substances into the brain have been reported using in vivo and in situ techniques (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). From such studies it is known that nonpolar substances rapidly enter the brain by diffusion whereas polar molecules do not enter except by selective carrier systems (6).…”

Section: Discussionmentioning

confidence: 99%

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Isolated microvessels: the blood-brain barrier in vitro.

Hjelle¹,

Baird-Lambert²,

Cardinale³

et al. 1978

Proc. Natl. Acad. Sci. U.S.A.

110

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Isolated bovine retinal and brain microvessels, exhibiting a patent lumen, were used to study the contribution of the microvasculature to the blood-brain and blood-retina barriers. The diffusion marker, sucrose, was taken up slowly by the isolated microvessels in contrast to leucine, tyrosine, and valine which were taken up at a considerably faster rate. Uptake of leucine was temperature dependent but resistant to inhibition by ouabain and sodium azide. The large neutral amino acids exhibited stereospecificity and cross-competition for uptake by the isolated microvessels. The apparent Kms for uptake for tyrosine, leucine, and valine were 111 M, 133 MM, and 500 M&M, respectively.The penetration into or removal of a substance from the central nervous system is a function of the interaction between that substance and the various brain barrier systems (1). These systems include the partitions between brain regions, various enzymatic barriers, the clearance and sink actions of the cerebrospinal fluid, choroid plexus and pial vessel transport, and partitioning at the blood-brain interface. From numerous morphological studies using dyes and electron-dense tracers, the barrier to the passage of substances from the blood into the brain has been thought to reside at the level of the intracerebral microvasculature (2). An indication that the microvascular endothelium, with its tight junctions, was the structural entity responsible for this barrier action and not the astrocytic processes adjacent to the microvessels was obtained when it was demonstrated that intraventricularly injected horseradish peroxidase appeared in the pericapillary space (3). Similarly, the impenetrability of the retinal microvasculature to dyes and electron-dense tracers (4) has been attributed to its endothelial tight junctions. In addition, both the retinal and brain microvascular endothelium have low rates of vesicle formation which further decreases the movement of molecules across this cell layer (5). Additional involvement of the cerebral microvasculature in blood-brain partitioning has been demonstrated by in situ carotid artery injection quickly followed by decapitation and determination of brain extraction of the injected test substance (6). Because of the short time interval between injection and decapitation, it has been assumed that the extraction of the test substance was an index of microvascular activity.To more directly characterize the role of the cerebral microvasculature in the partitioning of small molecules between the blood and the brain and to develop methods for the study of such phenomena in vitro, we examined isolated intracerebral bovine brain microvessels and the anatomically similar retinal microvessels for their abilities to exclude certain polar substances and to transport large neutral amino acids. Beef brains and enucleated eyes from yearling animals were obtained from a slaughterhouse, packed in ice, and taken to the laboratory within 30 min of death. MATERIALS AND METHODS MaterialsPreparation of Microvessels...

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Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

Isolated microvessels: the blood-brain barrier in vitro.

Hjelle¹,

Baird-Lambert²,

Cardinale³

et al. 1978

Proc. Natl. Acad. Sci. U.S.A.

110

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“…The perfusion medium was Krebs-Henseleit buffer containing 4% bovine serum albumin, bovine red blood cells at a hematocrit of 40, 5 mM glucose, 100 U/ml insulin, and amino acids at concentrations typical of rat plasma (3). Before use, the perfusate was warmed to 37°C, and the pH was adjusted to 7.40.…”

Section: Methodsmentioning

confidence: 99%

Phosphate uptake and PiT-1 protein expression in rat skeletal muscle

Abraham¹,

Brault²,

Terjung³

2004

American Journal of Physiology-Cell Physiology

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Skeletal muscle fiber types differ in their contents of total phosphate, which includes inorganic phosphate (P i) and high-energy organic pools of ATP and phosphocreatine (PCr). At steady state, uptake of Pi into the cell must equal the rate of efflux, which is expected to be a function of intracellular P i concentration. We measured 32 P-labeled Pi uptake rates in different muscle fiber types to determine whether they are proportional to cellular Pi content. Pi uptake rates in isolated, perfused rat hindlimb muscles were linear over time and highest in soleus (2.42 Ϯ 0.17, and lowest in white gastrocnemius (0.49 Ϯ 0.06Reasonably similar rates were obtained in vivo. Pi uptake rates at plasma Pi concentrations of 0.3-1.7 mM confirm that the P i uptake process is nearly saturated at normal plasma Pi levels. Pi uptake rate correlated with cellular Pi content (r ϭ 0.99) but varied inversely with total phosphate content. Sodium-phosphate cotransporter (PiT-1) protein expression in soleus and red gastrocnemius were similar to each other and seven-to eightfold greater than PiT-1 expression in white gastrocnemius. That the PiT-1 expression pattern did not match the pattern of P i uptake across fiber types implies that other factors are involved in regulating Pi uptake in skeletal muscle. Furthermore, fractional turnover of the cellular P i pool (0.67, 0.57, and 0.33 h Ϫ1 in soleus, red gastrocnemius, and white gastrocnemius, respectively) varies among fiber types, indicating differential management of intracellular Pi, likely due to differences in resistance to Pi efflux from the fiber. inorganic phosphate; sodium-inorganic phosphate transporters; PiT-2; inorganic phosphate efflux IN EVERY CELL, phosphate is necessary for structural and metabolic needs. In cellular energetics, phosphate forms the highenergy bonds of ATP and phosphocreatine (PCr), and inorganic phosphate (P i ) is a substrate for reactions in glycolysis, tricarboxylic acid cycle, and mitochondrial F 0 F 1 ATPase. Because cellular P i is a determinant of the free energy of ATP hydrolysis, its concentration is tightly controlled. However, alterations in total phosphate content in skeletal muscle, e.g., expansion of the PCr and/or reduction of the ATP pools, suggest that either P i uptake or P i loss from the cell is also modulated.In skeletal muscle, phosphate is distributed among the P i , ATP, and PCr pools primarily via ATPases, mitochondrial oxidative phosphorylation, and the creatine kinase reaction (21). Maintenance of the total phosphate contained in these pools depends on the balance of uptake and efflux of phosphate across the sarcolemma. Although most cellular phosphate is contained in organic phosphates, these molecules cannot easily cross the plasma membrane; rather, phosphate is transported as P i . Because P i is transported against a concentration and electrical gradient, it must be imported via active transport. This is presumably accomplished by the type III sodiumphosphate (Na-P i ) cotransporter (15) and is driven by the electrochemical ...

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“…The perfusion medium consisted of 5% bovine serum albumin in Krebs-Henseleit buffer, 5 mM glucose, 100 U/ml bovine insulin, and typical plasma concentrations of amino acids (3). Immediately before use, the perfusate was filtered (0.45 m), warmed to 37°C, and adjusted to a pH of 7.40.…”

Section: Hindquarter Perfusionmentioning

confidence: 99%

Muscle creatine uptake and creatine transporter expression in response to creatine supplementation and depletion

Brault

Abraham

Terjung

2003

Journal of Applied Physiology

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The total creatine pool size [Crtotal; creatine (Cr) + phosphocreatine (PCr)] is crucial for optimal energy utilization in skeletal muscle, especially at the onset of exercise and during intense contractions. The Crtotal likely is controlled by long-term modulation of Cr uptake via the sodium-dependent Cr transporter (CrT). To test this hypothesis, adult male Sprague-Dawley rats were fed 1% Cr, their muscle Crtotal was reduced by ∼85% [1% β-guanidinoproprionic acid (β-GPA)], or their muscle Crtotal was repleted (1% Cr after β-GPA depletion). Cr uptake was assessed by skeletal muscle 14C-Cr accumulation to Cr and PCr by using hindlimb perfusion, and CrT protein content was assessed by Western blot. Cr uptake rate decreased with dietary Cr supplementation in the white gastrocnemius (WG; 45%) only. Depletion of muscle Crtotal to ∼15% of normal increased Cr uptake in the soleus (21%) and red gastrocnemius (22%), corresponding to 70–150% increases in muscle CrT content. In contrast, the inherently lower Cr uptake rate in the WG was unchanged with depletion of muscle Crtotal even though CrT band density was increased by 230%. Thus there was no direct relationship between apparent muscle CrT abundance and Cr uptake rates. However, Cr uptake rates scaled inversely with decreases in muscle Crtotal in the high-oxidative muscle types but not in the WG. This implies that factors controlling Cr uptake are different among fiber types. These observations may help explain the influence of initial muscle Crtotal, time dependency, and variations in muscle Crtotal accumulation during Cr supplementation.

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The movement of amino acids between blood and skeletal muscle in the rat

Cited by 64 publications

References 17 publications

Isolated microvessels: the blood-brain barrier in vitro.

Isolated microvessels: the blood-brain barrier in vitro.

Phosphate uptake and PiT-1 protein expression in rat skeletal muscle

Muscle creatine uptake and creatine transporter expression in response to creatine supplementation and depletion

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