title: Alloxan cytotoxicity in vitro. Inhibition of rubidium ion pumping in pancreatic beta-cells.
abstract: Exposing micro-dissected pancreatic islets of non-inbred ob/ob mice to 2-5 mM-alloxan for 10 min decreased the ability of the islets to accumulate Rb+. Rb+ accumulation in pieces of exocrine pancreas was unaffected by alloxan. When islets were treated with alloxan in the presence of 2-20 mM-D-glucose, the Rb+-accumulating ability was protected in a dose-dependent manner. The protective action of D-glucose was reproduced with 3-O-methyl-D-glucose but not with L-glucose or D-mannoheptulose; mannoheptulose prevented D-glucose from exerting its protective action. The inhibition of Rb+ accumulation was due to a decreased inward pumping, since alloxan did not affect Rb+ efflux from pre-loaded islets. The inhibitory effect of alloxan had a latency of about 1 min, as revealed by experiments with dispersed islet cells in suspension. Alloxan-treated islets showed only a marginal decrease in ATP and no change in glucose 6-phosphate concentration. Although alloxan slightly decreased the hydrolysis of ATP in a subcellular fraction enriched in plasma membranes, this effect could not be attributed to a ouabain-sensitive adenosine triphosphatase. The plasma membranes exhibited a K+-activated hydrolysis of p-nitrophenyl phosphate; this enzyme activity too was insensitive to alloxan. Glucose may protect the univalent-cation pump by preventing permeation of alloxan via a path coupled to the hexose-transport system. Inhibition of the pump may be fundamental to the induction of alloxan-diabetes.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000496:Alloxan / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000201:enzymology; D002470:Cell Survival / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D005958:Glucosephosphates / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D012413:Rubidium / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D005958:Glucosephosphates; D000496:Alloxan; D000255:Adenosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose; D012413:Rubidium