The hepatic amino acid system A transport activity, is up-regulated in obese Zucker rats

A rapid method for the functional reconstruction of amino acid transport from liver plasma-membrane vesicles using the neutral detergent decanoyl-N-glucamide (‘MEGA-10’) is described. The method is a modification of that previously employed in this laboratory for reconstitution of amino acid transport systems from kidney brush-border membranes [Lynch & McGivan (1987) Biochem. J. 244, 503-508]. The transport activities termed ‘System A’, ‘System N’, and ‘System L’ are all reconstituted. The reconstitution procedure is rapid and efficient and is suitable as an assay for transport activity in studies involving membrane fractionation. By using this reconstitution procedure, System A transport activity was partially purified by lectin-affinity chromatography.

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Electrogenic Na+-dependentl-alanine transport in the lizard duodenum. Involvement of systems A and ASC

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2001.280.3.r612 ◽

2001 ◽

Vol 280 (3) ◽

pp. R612-R622

Author(s):

Virtudes Medina ◽

Antonio Lorenzo ◽

Mario Dı́az

Keyword(s):

Amino Acid ◽

Amino Acid Transport ◽

Short Circuit ◽

Duodenal Mucosa ◽

Neutral Amino Acid ◽

Acid Transport ◽

Transport Activity ◽

System A ◽

Alanine Transport ◽

Gallotia Galloti

l-Alanine transport across the isolated duodenal mucosa of the lizard Gallotia galloti has been studied in Ussing chambers under short-circuit conditions. Net l-alanine fluxes, transepithelial potential difference (PD), and short-circuit current ( Isc) showed concentration-dependent relationships. Na+-dependent l-alanine transport was substantially inhibited by the analog α-methyl aminoisobutyric acid (MeAIB). Likewise, MeAIB fluxes were completely inhibited byl-alanine, indicating the presence of system A for neutral amino acid transport. System A transport activity was electrogenic and exhibited hyperbolic relationships for net MeAIB fluxes, PD, and Isc, which displayed similar apparent K m values. Na+-dependentl-alanine transport, but not MeAIB transport, was partially inhibited by l-serine and l-cysteine, indicating the participation of system ASC. This transport activity represents the major pathway for l-alanine absorption and seemed to operate in an electroneutral mode with a negligible contribution to the l-alanine-induced electrogenicity. It is concluded from the present study that the active Na+-dependent l-alanine transport across the isolated duodenal mucosa of Gallotia galloti results from the independent activity of systems A and ASC for neutral amino acid transport.

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Adenohypophyseal response to hypophysiotropic hormones in male obese Zucker rats

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1985.249.4.e380 ◽

1985 ◽

Vol 249 (4) ◽

pp. E380-E384

Author(s):

M. L. Heiman ◽

J. R. Porter ◽

M. V. Nekola ◽

W. A. Murphy ◽

A. D. Hartman ◽

...

Keyword(s):

Growth Hormone ◽

Amino Acid ◽

Luteinizing Hormone ◽

Zucker Rats ◽

Pituitary Cells ◽

Response Curves ◽

Amino Acid Molecule ◽

Obese Zucker Rat ◽

Recessive Homozygote ◽

Obese Zucker Rats

Description of the recessive, homozygote obese Zucker rat (fafa) includes disorders of growth and reproduction. The aim of this study was to compare responsiveness of adenohypophyseal cells, obtained from male fafa rats and from their lean siblings, to growth hormone-releasing factor (GRF) and to luteinizing hormone-releasing hormone (LHRH). Pituitary cells were cultured for 4 days and were then challenged with either GRF-29 (the NH2-terminal 29 amino acid GRF peptide that expresses full biological activity of its parent 44 amino acid molecule) or [D-Trp6]LHRH (LHRH-A, an LHRH agonist). Medium was assayed for growth hormone (GH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) by radioimmunoassay. Dose-response curves were compared using the computer program ALLFIT. The median effective GRF-29 concentration (EC50) computed for hypophyseal cells cultured from lean animals (0.30 +/- 0.01 fM; means +/- SE of 4 experiments) was less (P less than 0.01) than that calculated for cells obtained from fafa rats (15.8 +/- 6.7 fM). In contrast, cells derived from lean littermates required a larger (EC50) concentration of LHRH-A than did gonadotrophs cultured from obese rats [58.2 +/- 1.2 vs. 10.7 +/- 1.2 pM (P less than 0.01) and 59.4 +/- 10.4 vs. 15.7 +/- 7.6 pM (P less than 0.05)] to secrete LH and FSH, respectively. Our data describe an attenuated pituitary response to GRF-29 and an enhanced response to LHRH-A in the fafa.

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