Fluxes and distribution of calcium in rat liver cells: kinetic analysis and identification of pools

• Published in: The Journal of physiology Vol. 272; no. 3; pp. 529 - 552
• Main Authors: Claret-Berthon, Brigitte, Claret, M., Mazet, J. L.
• Format: Journal Article
• Language: English
• Published: England The Physiological Society 01.11.1977
• Subjects: Animals; Biological Transport, Active - drug effects; Calcium - metabolism; Edetic Acid - pharmacology; Egtazic Acid - pharmacology; In Vitro Techniques; Kinetics; Lanthanum - pharmacology; Liver - cytology; Liver - metabolism; Mitochondria, Liver - metabolism; Models, Biological; Rats
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1977.sp012058

1. Fluxes and distribution of Ca were studied in the perfused rat liver. Kinetic analysis of 45 Ca exchange revealed three compartments with time constants of 4, 14 and 223 min, pool sizes of 250, 385 and 670 μmole.kg -1 wet wt. respectively, and one non-exchangeable compartment of 400 μmole.kg -1 . 2. 45 Ca uptake by in situ mitochondria followed, as a function of cell loading time, a mono-exponential function with a time constant of 16 min. This suggests that the second compartment may be identified as the intracellular pool of Ca. The calculated cell transmembrane flux of Ca was 28 μmole.kg -1 min -1 or 0·17 p-mole.cm -2 .sec -1 . 3. The maximum 45 Ca uptake by in situ mitochondria was 2·3 n-mole.mg -1 of protein which represents, on the basis of 50 mg of mitochondrial protein per g of fresh liver, 115 μmole.kg -1 or 30% of the cytoplasmic pool. A pool of 10·8 n-mole.mg -1 protein (or 540 μmole.kg -1 ) of non-exchangeable Ca (at steady state) was probably in the form of Ca phosphate precipitated in the mitochondrial matrix. 4. Extracellular Ca pools were studied using competitor of Ca binding (La) or Ca chelators (EGTA). La displaced specifically a homogeneous pool of Ca (τ = 5·1 min) which represented a fraction (55 μmole.kg -1 ) of the rapidly exchangeable Ca (first compartment) without perturbing other external pools. On the other hand, EGTA displaced completely that compartment, and about 85% of the Ca of the third compartment. These results suggest that the first and the major fraction of the third compartments are extracellular. They account for 63% of total exchangeable Ca. 5. A model of distribution and exchange of Ca in hepatocytes is proposed.