Vanadate stimulates system A amino acid transport activity in skeletal muscle. Evidence for the involvement of intracellular pH as a mediator of vanadate action.

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.

Download Full-text

Effect of Na+ electrochemical potential energy on system A Amino acid transport in rat skeletal muscle during endotoxic shock

Amino Acids ◽

10.1007/978-94-011-2262-7_9 ◽

1990 ◽

pp. 71-80

Author(s):

Michael D. Karlstad ◽

John T. Chesney

Keyword(s):

Skeletal Muscle ◽

Amino Acid ◽

Potential Energy ◽

Amino Acid Transport ◽

Endotoxic Shock ◽

Electrochemical Potential ◽

Acid Transport ◽

Rat Skeletal Muscle ◽

System A

Download Full-text

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.

Download Full-text

Effects of prior exercise on the action of insulin-like growth factor I in skeletal muscle

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1992.263.2.e340 ◽

1992 ◽

Vol 263 (2) ◽

pp. E340-E344 ◽

Cited By ~ 5

Author(s):

E. J. Henriksen ◽

L. L. Louters ◽

C. S. Stump ◽

C. M. Tipton

Keyword(s):

Skeletal Muscle ◽

Amino Acid ◽

Growth Factor ◽

Glucose Transport ◽

Amino Acid Transport ◽

Acid Transport ◽

Factor I ◽

System A ◽

Prior Exercise ◽

Igf I

Prior exercise increases insulin sensitivity for glucose and system A neutral amino acid transport activities in skeletal muscle. Insulin-like growth factor I (IGF-I) also activates these transport processes in resting muscle. It is not known, however, whether prior exercise increases IGF-I action in muscle. Therefore we determined the effect of a single exhausting bout of swim exercise on IGF-I-stimulated glucose transport activity [assessed by 2-deoxy-D-glucose (2-DG) uptake] and system A activity [assessed by alpha-(methylamino)isobutyric acid (MeAIB) uptake] in the isolated rat epitrochlearis muscle. When measured 3.5 h after exercise, the responses to a submaximal concentration (0.2 nM), but not a maximal concentration (13.3 nM), of insulin for activation of 2-DG uptake and MeAIB uptake were enhanced. In contrast, prior exercise increased markedly both the submaximal (5 nM) and maximal (20 nM) responses to IGF-I for activation of 2-DG uptake, whereas only the submaximal response to IGF-I (3 nM) for MeAIB uptake was enhanced after exercise. We conclude that 1) prior exercise significantly enhances the response to a submaximal concentration of IGF-I for activation of the glucose transport and system A neutral amino acid transport systems in skeletal muscle and 2) the enhanced maximal response for IGF-I action after exercise is restricted to the signaling pathway for activation of the glucose transport system.

Download Full-text

Prolonged incubation of skeletal muscle increases system A amino acid transport

AJP Cell Physiology ◽

10.1152/ajpcell.1991.260.1.c88 ◽

1991 ◽

Vol 260 (1) ◽

pp. C88-C95 ◽

Cited By ~ 13

Author(s):

E. A. Gulve ◽

G. D. Cartee ◽

J. H. Youn ◽

J. O. Holloszy

Keyword(s):

Skeletal Muscle ◽

Amino Acids ◽

Amino Acid ◽

Amino Acid Transport ◽

Time Dependent ◽

Acid Transport ◽

Minimum Essential Medium ◽

Prolonged Incubation ◽

System A ◽

Nonessential Amino Acids

During the course of experiments involving prolonged incubation of skeletal muscle, we observed large increases in system A amino acid transport activity. System A activity was monitored with the nonmetabolizable amino acid analogue alpha-(methylamino)isobutyrate (MeAIB). When rat epitrochlearis muscles are incubated in Krebs-Henseleit buffer supplemented with 0.1% bovine serum albumin and 8 mM glucose, basal MeAIB transport doubles after 5 h and is elevated approximately sevenfold after 9 h compared with rates measured in muscles incubated for 1 h. Insulin-stimulated transport also doubles after 5 h and increases by fourfold after 9 h. The increases in basal and insulin-stimulated system A transport over time can be prevented by incubating muscles in the presence of cycloheximide. Addition of minimum essential medium essential amino acids (EAA) to the incubation medium blocks the increase in basal and insulin-stimulated MeAIB transport measured after 9 h by 85-90 and 60%, respectively. A single amino acid, glutamine, can account for half of the inhibitory effect of EAA on the time-dependent increase in basal system A transport. Amino acid metabolism is not necessary for inhibition of the rise in basal MeAIB transport. At concentrations normally present in minimum essential medium, nonessential amino acids are less effective (51% inhibition) in preventing the rise in basal transport occurring over 9 h. At three times normal concentrations, however, the ability of nonessential amino acids to prevent the time-dependent increases in basal and insulin-stimulated MeAIB transport is comparable to that of EAA. These changes in MeAIB transport with prolonged incubation are not due to muscle deterioration.(ABSTRACT TRUNCATED AT 250 WORDS)

Download Full-text