Evidence for two compartments of exchangeable calcium in isolated rat liver mitochondria obtained using a /sup 45/Ca exchange technique in the presence of magnesium, phosphate, and ATPase at 37/sup 0/C
The distribution of calcium between isolated rat liver mitochondria and the extramitochondrial medium at 37 degrees C and in the presence of 2 mM inorganic phosphate, 3 mM ATP, 0.05 or 1.1 mM free magnesium and a calcium buffer, nitrilotriacetic acid, was investigated using a /sup 45/Ca exchange technique. The amounts of /sup 40/Ca in the mitochondria and medium were allowed to reach equilibrium before initiation of the measurement of /sup 45/Ca exchange. At 0.05 mM free magnesium and initial extramitochondrial free calcium concentrations of between 0.15 and 0.5 microM, the mitochondria accumulated calcium until the extramitochondrial free calcium concentration was reduced to 0.15 microM. Control experiments showed that the mitochondria were stable under the incubation conditions employed. The /sup 45/Ca exchange data were found to be consistent with a system in which two compartments of exchangeable calcium are associated with the mitochondria. Changes in the concentration of inorganic phosphate did not significantly affect the /sup 45/Ca exchange curves, whereas an increase in the concentration of free magnesium inhibited exchange. The maximum rate of calcium outflow from the mitochondria was estimated to be 1.7 nmol/min per mg of protein, and the value of K0.5 for intramitochondrial exchangeable calcium to be about 1.6 nmol per mg of protein. Ruthenium Red decreased the fractional transfer rate for calcium inflow to the mitochondria while nupercaine affected principally the fractional transfer rates for the transfer of calcium between the two mitochondrial compartments. The use of the incubation conditions and /sup 45/Ca exchange technique described in this report for studies of the effects of agents which may alter mitochondrial calcium uptake or release (e.g., the pre-treatment of cells with hormones) is briefly discussed.
- OSTI ID:
- 5451356
- Journal Information:
- J. Membr. Biol.; (United States), Vol. 62:1-2
- Country of Publication:
- United States
- Language:
- English
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CALCIUM
BIOCHEMICAL REACTION KINETICS
CALCIUM 45
ISOTOPE APPLICATIONS
MITOCHONDRIA
PHYSIOLOGY
ATP
CALCIUM 40
COMPARTMENTS
MAGNESIUM
PHOSPHATES
UPTAKE
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM ISOTOPES
CELL CONSTITUENTS
DAYS LIVING RADIOISOTOPES
ELEMENTS
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
INTERMEDIATE MASS NUCLEI
ISOTOPES
KINETICS
LIGHT NUCLEI
METALS
NUCLEI
NUCLEOTIDES
ORGANIC COMPOUNDS
ORGANOIDS
OXYGEN COMPOUNDS
PHOSPHORUS COMPOUNDS
RADIOISOTOPES
REACTION KINETICS
STABLE ISOTOPES
550201* - Biochemistry- Tracer Techniques
551001 - Physiological Systems- Tracer Techniques
550301 - Cytology- Tracer Techniques