Transport of ascorbic acid and dehydroascorbic acid by pancreatic islet cells from neonatal rats

• Published in: Biochemical journal Vol. 274; no. 3; pp. 739 - 744
• Main Authors: AN ZHOU, NIELSEN, J. H, FARVER, O, THORN, N. A
• Format: Journal Article
• Language: English
• Published: Colchester Portland Press 15.03.1991
• Subjects: Animals; Animals, Newborn; ascorbic acid; Ascorbic Acid - metabolism; Biological and medical sciences; Biological Transport; Cell physiology; Cytoplasmic Granules - metabolism; dehydroascorbic acid; Dehydroascorbic Acid - metabolism; Fundamental and applied biological sciences. Psychology; Glucocorticoids - pharmacology; Glucose - pharmacology; In Vitro Techniques; Ions; Islets of Langerhans - drug effects; Islets of Langerhans - metabolism; Membrane and intracellular transports; Metals; Molecular and cellular biology; Rats; Rats, Inbred Strains; Ascorbic acid; Radiolabelling; Rat; Biological transport; Rodentia; Glucose; Vertebrata; Mammalia; Ascorbic acid derivatives; Langerhans cell; Sodium; Newborn animal; Peptidylglycine monooxygenase; Hormonal regulation; Pancreas
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj2740739

Several amidated biologically active peptides such as pancreastatin, thyrotropin-releasing hormone, pancreatic polypeptide and amylin are produced in endocrine pancreatic tissue which contains the enzyme necessary for their final processing, i.e. peptidylglycine alpha-amidating mono-oxygenase (EC 1.14.17.3). The enzyme needs ascorbic acid for activity as well as copper and molecular oxygen. The present work shows that pancreatic islet cells prepared from overnight cultures of isolated islets from 5-7-day-old rats accumulate 14C-labelled ascorbic acid by a Na(+)-dependent active transport mechanism which involves a saturable process (estimated Km 17.6 microM). Transport was inhibited by ouabain, phloridzin, cytochalasin B, amiloride and probenecid. Glucose inhibited or stimulated uptake, depending on the length of incubation time of the cells. The uptake of dehydroascorbic acid was linearly dependent on concentration. Dehydroascorbic acid was converted to ascorbic acid by an unknown mechanism after uptake. The uptake of both ascorbic acid and dehydroascorbic acid was inhibited by tri-iodothyronine, and uptake of ascorbic acid, but not of dehydroascorbic acid, was inhibited by glucocorticoids. Isolated secretory granules contained a fairly low concentration of iron but a high concentration of copper.