The uptake of amino acids by isolated segments of rat intestine II. A survey of affinity for uptake from rates of uptake and competition for uptake

Finch, Lloyd R.; Hird, F. J. R.

doi:10.1016/0006-3002(60)90438-8

Cited by 136 publications

(39 citation statements)

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“…In agreement with findings obtained with segments from adult rats [14] and Ehrlich ascites cells [17], the rates of accumulation of glutamic acid and aspartic acid by the segments from 2-day-old rats were very low (Table III). The amide of aspartic acid, asparagine, had a rate of accumulation about 10 times greater than that of the free acid.…”

Section: Resultssupporting

confidence: 90%

“…Replacement of a hydrogen in a methyl group of alanine with the negatively charged hydrophilic carboxylate group to form aspartic acid virtually abolishes amino acid accumulation. Removal of the net negative charge and most of the hydrophilic properties of the side chain of aspartic acid by formation of the amide asparagine results in reappearance of active accumulation, presumably by the neutral amino acid pathway [14]. The slow accumulation of histidine as compared with other neutral amino acids that was noted in this study has also been reported for adult rat intestine [14] and this also seems to be due to structural considerations.…”

Section: Discussionsupporting

confidence: 75%

“…(9) 0.28 ± 0.06 L-Asparagine (10) 2.88 ± 0.29 cumulation of lysine after 5 min is a linear function of time [26]. Since the apparent K m 's of lysine and arginine for the basic amino acid carrier are at least as low as the corresponding K m 's of the neutral amino acids for their carrier [14,18,26,30], this lowered accumulation rate could not be attributed to differences in affinity for the carriers. On the basis of unpaired difference Mests, the accumulation of the nonessential amino acid ornithine was found to be identical to that of the essential amino acid lysine but statistically greater than that of the essential amino acid arginine (P < 0.01).…”

Section: Resultsmentioning

confidence: 99%

“…Intestinal segments were essentially free of luminal contents and usually weighed 100-300 mg. The segments were then placed in 5 ml oxygenated Krebs-Tris buffer (pH 7.4) that contained 118 HIM NaCl, 25 HIM Tris-HCl, 4.7 HIM KC1, 2.5 HIM CaCl 2 , 1.2 mwc MgSO 4 , 1.2 HIM KH 2 PO 4 and 8,000-12,000 counts/min per milliliter of 14 C-labeled and nonradioactive amino acid to the desired final concentration. In addition, 10,000-15,000 counts/min per milliliter of methoxy-3 H-inulin were added to the medium to measure the extracellular space of the tissue [32].…”

Section: Methodsmentioning

confidence: 99%

“…The spectrometer was adjusted to permit 60% 14 C efficiency, 22% 3 H efficiency, less than 0.01% 3 H efficiency on the 14 C channel, and 10% 14 C efficiency on the 3 H channel. Amino acid transport is expressed as intracellular accumulation which is defined as the millimolar concentration of the amino acid in the cellular water after a given incubation period.…”

Section: Methodsmentioning

confidence: 99%

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Amino Acid Transport Pathways in the Small Intestine of the Neonatal Rat

1972

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ExtractThe activity of amino acid transport pathways in the small intestine of the 2-day-old rat was investigated. Transport was determined by measuring the uptake of 1 mM concentrations of various amino acids by intestinal segments after a 5-or 10-min incubation and it was expressed as intracellular accumulation.The neutral amino acid transport pathway was well developed with intracellular accumulation values for leucine, isoleucine, valine, methionine, tryptophan, phenylalanine, tyrosine, and alanine ranging from 3.9-5.6 mM/5 min. The intracellular accumulation of the hydroxy-containing neutral amino acids threonine (essential) and serine (nonessential) were 2.7 mM/5 min, a value significantly lower than those of the other neutral amino acids. The accumulation of histidine was also well below the level for the other neutral amino acids (1.9 mM/5 min). The basic amino acid transport pathway was also operational with accumulation values for lysine, arginine and ornithine ranging from 1.7-2.0 mM/5 min. Accumulation of the essential amino acid lysine was not statistically different from that of nonessential ornithine. Accumulation of aspartic and glutamic acid was only 0.24-0.28 mM/5 min indicating a very low activity of the acidic amino acid transport pathway. Accumulation of sarcosine and betaine was about 0.5 mM/5 min, which indicates a low activity for the imino acid-glycine pathway. The presence of 1 HIM alanine significantly (P < 0.01) increased the accumulation of lysine by 28.5%, which suggests the presence of an exchange transport system. These results show that by operation of the neutral and basic amino acid transport systems, the neonatal rat can effectively absorb all the essential amino acids; however, accumulation of individual amino acids appears to be governed by structural rather than nutritional considerations. SpeculationThe data presented demonstrate the differential ability of the neonatal rat to absorb various ammo acids. This finding is of potential importance in the formulation and evaluation of synthetic protein diets. IntroductionThe quality and quantity of dietary protein which would result in optimal growth and development of infants at a reasonable cost is a subject that has been discussed by nutritionists for several decades. Such discussion stimulated investigation of intestinal transport at, or shortly after birth [4-6, 13, 15, 30].A recent article by the authors [15] characterized the 713

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Section: Resultssupporting

confidence: 90%

Section: Discussionsupporting

confidence: 75%