title: Studies on the energy-linked Ca2+ accumulation in pig heart mitochondria - role of Mg2'ons.
abstract: Comparative intracellular distribution of Ca2+, Mg2+ and adenine nucleotides has been studied in pig heart by differential centrifugation or fractional extraction and has shown that Mg2+ and ATP are associated mainly with soluble fractions whereas Ca2+ and ADP are more tightly bound to subcellular structures. Ca2+ accumulation and Ca2+ stimulated respiration were studied in pig heart mitochondria under different energetic conditions in the absence or presence of phosphate. Ca2+ concentrations of about 1200 nmoles/mg protein inhibit Ca2+ accumulation, site I substrate oxidation and induce an efflux of mitochondrial Mg2+. These deleterious effects of Ca2+ on respiration occur even in the absence of phosphate or oxidizable substrate; they are completely prevented by ruthenium red only, and partially prevented by the addition of M2+ to the medium. The kinetics of Ca2+ uptake become of the sigmoidal type when Mg2+ is present. This cation strongly inhibits the rate of Ca2+ uptake in the presence of added phosphate and decreases the affinity of Ca2+ for its transport system. In the absence of phosphate, Mg2+ has no effect on Ca2+ uptake. The possible physiological implications of these findings are discussed
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005971:Glutamates / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008634:Mersalyl / Q000494:pharmacology; D008929:Mitochondria, Heart / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D010710:Phosphates / Q000494:pharmacology; D012430:Ruthenium Red / Q000494:pharmacology; D013552:Swine
chemical_list: D000227:Adenine Nucleotides; D005971:Glutamates; D010710:Phosphates; D012430:Ruthenium Red; D008634:Mersalyl; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium