Catalytic Activities of Salicylaldehyde Derivatives. II. Kinetic Studies of the Racemization of Amino Acid

Little is known concerning the expression of amino acid transporters during intestinal epithelial cell differentiation. The transport mechanism ofl-glutamate and its regulation during the differentiation process were investigated using the human intestinal Caco-2 cell line. Kinetic studies demonstrated the presence of a single, high-affinity,d-aspartate-sensitive l-glutamate transport system in both confluent and fully differentiated Caco-2 cells. This transport was clearly Na+ dependent, with a Hill coefficient of 2.9 ± 0.3, suggesting a 3 Na+-to-1 glutamate stoichiometry and corresponding to the well-characterized XA,G − system. The excitatory amino acid transporter (EAAT)1 transcript was consistently expressed in the Caco-2 cell line, whereas the epithelial and neuronal EAAT3 transporter was barely detected. In contrast with systems B0 and y+, which have previously been reported to be downregulated when Caco-2 cells stop proliferating, l-glutamate transport capacity was found to increase steadily between day 8 and day 17. This increase was correlated with the level of EAAT1 mRNA, which might reflect an increase in EAAT1 gene transcription and/or stabilization of the EAAT1 transcript.

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Leucine kinetics from [2H3]- and [13C]leucine infused simultaneously by gut and vein

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1991.260.1.e111 ◽

1991 ◽

Vol 260 (1) ◽

pp. E111-E117 ◽

Cited By ~ 12

Author(s):

R. A. Hoerr ◽

D. E. Matthews ◽

D. M. Bier ◽

V. R. Young

Keyword(s):

Amino Acid ◽

Human Subjects ◽

Kinetic Studies ◽

Tracer Study ◽

Experimental Diet ◽

Fed State ◽

Leucine Kinetics ◽

Tracer Kinetic ◽

Plasma Leucine ◽

Plasma Compartment

In amino acid tracer kinetic studies of the fed state, ingested amino acid may be taken up during its initial transit through splanchnic tissues and thus not enter the plasma compartment where tracer is infused. To investigate this possibility, adult human subjects received simultaneous intravenous (iv) and intragastric (ig) leucine tracer infusions, first during a postabsorptive (PA) 4-h primed continuous ig infusion of L-[1-13C]-leucine and L-[5,5,5-2H3]leucine iv, followed on a separate day by a fed infusion, in which an ig infusion of a liquid formula was started 2 h before the tracer infusion and continued throughout the tracer study. Subjects were accustomed to a constant experimental diet supplying 1.5 g protein.kg-1.day-1 and 41-45 kcal.kg-1.day-1 for 7 and 12 days before the PA and fed studies, respectively. For the PA study, plasma enrichment for the ig tracer was 3.34 +/- 0.27 (SE) mol + excess and for the iv tracer it was 4.18 +/- 0.10 (P less than 0.02). Enrichments of alpha-keto-isocaproic acid (KIC) were 3.24 +/- 0.16 (ig) and 3.02 +/- 0.14 (iv), respectively [not significant (NS)]. For the fed study, plasma leucine enrichment for the ig tracer was 2.15 +/- 0.14 and for the iv tracer was 2.84 +/- 0.09 (P less than 0.02). KIC enrichments were 2.02 +/- 0.08 (ig) and 2.24 +/- 0.08 (iv), respectively (NS). In the PA study, the ratio of the plasma leucine enrichments for the ig and iv tracers was 0.80 +/- 0.06 and in the fed experiment, 0.76 +/- 0.05, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

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