Effects of anions, pH and magnesium on calcium accumulation and release by sarcoplasmic reticulum vesicles.
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.
Sorenson
M M
MM
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.
De Meis
L
L
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
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