title: Characterization of an ATP-dependent Ca2+ uptake system in mouse pancreatic microsomes.
abstract: The uptake of 45Ca2+ was studied in microsomes prepared from isolated mouse pancreatic acini. These microsomes accumulated 45Ca2+ in the presence of ATP; uptake was potentiated by addition of oxalate. Sequestered microsomal 45Ca2+ was only gradually removed by ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) but was readily released by the divalent cation ionophore A23187. Inhibitors of mitochondrial oxidation and mitochondrial calcium transport had little effect on microsomal 45Ca2+ uptake. A separate subcellular fraction enriched in plasma membranes took up 45Ca2+ poorly compared with the microsomal fraction. Half-maximal 45Ca2+ uptake by the microsomal fraction was observed at a free Ca2+ concentration of 1.1 microM. 45Ca2+ uptake was dependent on Mg-ATP and showed a pH optimum at 6.8-7.0. Subfractionation of the total microsomes into "heavy" and "light" microsomal fractions indicated higher 45Ca2+ uptake activity associated with the heavy fraction. A Ca2+-activated, Mg2+-dependent ATPase was demonstrated in this fraction. Stimulation of pancreatic acini with the cholecystokinin analogue caerulein prior to homogenization increased the subsequent rate of 45Ca2+ uptake by the microsomal fraction.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D051379:Mice; D008861:Microsomes / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism; D010070:Oxalates / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism
chemical_list: D010070:Oxalates; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D009245:NADH Dehydrogenase; D003576:Electron Transport Complex IV; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium