Maintenance of glucagon-stimulated system A amino acid transport activity in rat liver plasma membrane vesicles

• Published in: Biochimica et biophysica acta Vol. 856; no. 3; pp. 428 - 436
• Main Authors: SCHENERMAN, M. A, KILBERG, M. S
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier 25.04.1986; North-Holland
• Subjects: Amino Acids - metabolism; Aminoisobutyric Acids - metabolism; Aminoisobutyric Acids - pharmacology; Animals; Biological and medical sciences; Biological Transport - drug effects; Cell Membrane - metabolism; Cell physiology; Fundamental and applied biological sciences. Psychology; Glucagon - pharmacology; In Vitro Techniques; Kinetics; Liver - drug effects; Liver - metabolism; Male; Membrane and intracellular transports; Molecular and cellular biology; Rats; Rats, Inbred Strains; Sodium - pharmacology; Vertebrata; Regulation(control); Mammalia; Glucagon; Hepatocyte; Rat; Membrane transport; Aminoacid; Rodentia; Plasma membrane
• ISSN: 0006-3002; 1878-2434
• DOI: 10.1016/0005-2736(86)90133-1

Plasma membrane vesicles prepared from intact rat liver or isolated hepatocytes retain transport activity by systems A, ASC, N, and Gly. Selective substrates for these systems showed a Na+-dependent overshoot indicative of energy-dependent transport, in this instance, driven by an artificially-imposed Na+ gradient. Greater than 85% of Na+-dependent 2-aminoisobutyric acid (AIB) uptake was blocked by an excess of 2-(methylamino)isobutyric acid (MeAIB) with an apparent Ki of 0.6 mM. Intact hepatocytes obtained from glucagon-treated rats exhibited a stimulation of system A activity and plasma membrane vesicles isolated from those same cells partially retained the elevated activity. Transport activity induced by substrate starvation of cultured hepatocytes was also evident in membrane vesicles prepared from those cells. The membrane-bound glucagon-stimulated system A activity decays rapidly during incubation of vesicles at 4 degrees C (t1/2 = 13 h), but not at -75 degrees C. Several different inhibitors of proteolysis were ineffective in blocking the decay of transport activity. Hepatic system N transport activity was also elevated in plasma membrane vesicles from glucagon-treated rats, whereas system ASC was essentially unchanged. The results indicate that both glucagon and adaptive regulation cause an induction of amino acid transport through a plasma membrane-associated protein.