title: Effects of anions, pH and magnesium on calcium accumulation and release by sarcoplasmic reticulum vesicles.
abstract: In the absence of oxalate, Ca2+ accumulation by isolated sarcoplasmic reticulum vesicles may show a transient behavior in which the vesicles accumulate during the first 2 min of incubation as much as twice the amount of Ca2+ which is retained after 5-7 min, when Ca2+ accumulation approaches a steady state. Before Ca2+ release begins, the Ca2+ accumulation can reach 200-250 nmol/mg protein. The spontaneous release of the "extra" Ca2+ initially accumulated appears to be triggered by the attainment of a sufficiently high concentration of free Ca2+ inside the vesicles. The amplitude of the transient phase of Ca2+ accumulation reaches a high value near pH 6.0 and is increased by free Mg2+. At optimal concentrations of H+ and Mg2+, the amount of Ca2+ accumulated during the transient is augmented by various anions, in the order maleate > or = propionate > or = succinate > chloride > sulfate > acetylglycine. The divalent anions have their maximum effects at 20-40 mM and the monovalent anions, at 40-200 mM. At 200 mM, all of the carboxylic anions tested significantly reduce the amount of Ca2+ retained in the steady state.
authors.affiliation: Instituto de Biofisica, Centro de Ciencias da Saude, Bloco G, Universidade Federal do Rio de Janeiro, Ilha do Fundao, Cidade Universitaria, ZC 32, Rio de Janeiro, RJ 20.000, Brasil.
authors.forename: M M
authors.initials: MM
authors.lastname: Sorenson
authors.forename: L
authors.initials: L
authors.lastname: De Meis
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000838:Anions; D001703:Biophysics / Q000379:methods; D002118:Calcium / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D017616:Magnesium Compounds / Q000737:chemistry; D008298:Maleates / Q000494:pharmacology; D011422:Propionates / Q000494:pharmacology; D011522:Protons; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D019802:Succinic Acid / Q000494:pharmacology; D013431:Sulfates / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000838:Anions; D002712:Chlorides; D017616:Magnesium Compounds; D008298:Maleates; D011422:Propionates; D011522:Protons; D013431:Sulfates; D000255:Adenosine Triphosphate; C030272:maleic acid; D019802:Succinic Acid; D008274:Magnesium; D002118:Calcium; D005998:Glycine