title: Kinetics of high-affinity Ca2+ sequestration in permeabilized rat pancreatic acini.
abstract: Energy-dependent subcellular Ca2+ sequestration was studied in the presence of ruthenium red using rat pancreatic acini, which had been permeabilized by exposure to medium nominally free of Ca2+. The initial rate of Ca2+ uptake (approximately 2,800 pmol.min-1.mg acinar protein-1) quickly slowed, and a mean steady-state Ca2+ content of approximately 3,000 pmol/mg was reached after 5-10 min of incubation at 37 degrees C. Ca2+ uptake was stimulated by submicromolar Ca2+ concentrations (K0.5 = 156 nM); required Mg2+-ATP (K0.5 = 0.78 mM) was greatest at a pH of 7.0 and was abolished by the Ca2+ ionophore A23187. Other nucleotide phosphates as well as p-nitrophenylphosphate were relatively poor substrates, supporting Ca2+ uptake at initial rates that were 6-14% of those measured in the presence of ATP. These results show that pancreatic acini permeabilized without detergents possess a nonmitochondrial Ca2+ transporting system not located in the plasma membrane but with the properties expected of a major regulator of acinar cytosolic Ca2+ concentration.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008297:Male; D010179:Pancreas / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012430:Ruthenium Red / Q000378:metabolism; D013997:Time Factors
chemical_list: D012430:Ruthenium Red; D000255:Adenosine Triphosphate; D002118:Calcium