title: Kinetic properties of exchangeable calcium in guinea-pig heart mitochondria measured at low concentrations of free calcium and in the presence of Mg2+, ATP4- and inorganic phosphate.
abstract: The kinetic properties of exchangeable Ca2+ in isolated guinea-pig heart mitochondria were studied at 25 degrees C in the presence of 0.9 mM free Mg2+, ATP, phosphate ions and 0.4 - 0.5 microM free Ca2+ using a 45Ca2+ exchange technique. The simplest system which was found to be consistent with the data was one in which two kinetically-distinct compartments of exchangeable Ca2+ are present in the mitochondria. In the presence of 6 mM Na and at 0.4 microM free Ca2+, the fractional transfer rates for the transport of Ca2+ from these compartments were found to be 0.6 and 0.05 min-1 and the quantities of exchangeable Ca2+ 0.04 and 0.2 mumol/g wet wt heart, respectively. The amount of 45Ca2+ exchanged increased when the concentration of inorganic phosphate was increased, and decreased slightly when the concentration of free Mg2+ was increased from 1 mM to 3 mM. The flux of Ca2+ across the boundaries of both compartments was inhibited by an increase in the concentration of extramitochondrial Na+. The contribution of mitochondrial Ca2+ to compartments of kinetically-distinct exchangeable Ca2+ observed in intact cardiac muscle is briefly discussed.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000032:analysis*; D004305:Dose-Response Relationship, Drug; D006168:Guinea Pigs; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008929:Mitochondria, Heart / Q000032:analysis* / Q000187:drug effects; D010710:Phosphates / Q000494:pharmacology*; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D010710:Phosphates; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium