Net Movements of Calcium and Magnesium in Slices of Rat Liver

Abstract

Rat liver slices incubated at IoC in phosphate (10 mM) or bicarbonate (25 mM) plus phosphate (2 mM)-buffered Ringer's solutions containing 1.2 rnM Ca s4 underwent a 5-fold increase in Ca 2+ content relative to their fat-free solids, and lost 10 % of their Mg ~+. Upon subsequent incubation at 380C, slices in the bicarbonate medium lost about half of the accumulated Ca ~-. This extrusion was less efficient in the phosphate medium. Succinate (40 re_M), which strongly stimulated respiration, caused an accumulation of Ca ~+ in slices incubated in the phosphate medium. The extrusion of Ca ~+ was prevented by respiratory inhibitors, but not by inhibition of the Na + and K + transport (by ouabain or K+-free medium). This suggests that the Ca ~+ transport was itself directly dependent on high-energy compounds and was not due to a heteroexchange diffusion of Ca ~+ against Na + ions. Some evidence was obtained for the occurrence of an active accumulation of Mg ~" ions.

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

“…The Ca content of liver does not change appreciably over a period of 2-5 hr, indicating that experiments can be carried out under steady-state conditions during this period of time. The mean total contents of Ca, Na and K in liver tissue do not significantly differ from those measured in slices or in vivo (Wallach et al 1966;Van Rossum, 1970;Williams & Woodbury, 1971;McLaughlin, 1973). Since the concentration of Ca in the medium was 2-16 mm and the extracellular space as measured by [14C]inulin was 25 %, the total cellular content was about 1-70 mmole.kg-' wet liver (wet wt.)…”

“…kg-') is roughly equivalent This value may be compared with that of the strongly bound Ca fraction of liver slices which is about 700 molee . kg-' (recalculation of results of Wallach et al (1966) and Van Rossum (1970)). The theoretical uptake and unloading of 45Ca in each of the three compartments (Car, t) are illustrated in Fig.…”

“…In agreement with this hypothesis, no (Ca)-Mg-ATPase activity of the kind thought to be associated with active extrusion of Ca has been found in isolated liver plasma membranes (Chambault, Leray-Pecker, Feldman & Hanoune, 1974). However, in an extensive study on Ca movements in liver slices, Van Rossum (1970) showed that the net outward transport of Ca does not depend on Na pump activity or upon Na concentration gradient. Moreover, he demonstrated that Ca transport has a primary dependence on respiratory energy.…”

Vascularly Perfused Frog Lung: Effects of Metabolic Conditions on Adenine Nucleotides and Inorganic Ions

“…The lung samples collected in weighing bottles were weighed before and after drying overnight at 105°C to determine their water content and dry weight. Ions were extracted from the dry tissue with 3 ml 0 1 N-HNO3 (Whittam, 1955;Little, 1964;van Rossum, 1970). Cations were estimated by flame emission photometry (Na+ and K+) or atomic absorption spectrometry (Ca2+ and Mg2+) using a Perkin-Elmer model 2380 atomic absorption spectrophotometer.…”

“…This diuretic agent inhibits co-transport of Na+ and Cl-in a number of epithelial tissues (Frizzell, Field & Schultz, 1979) but has also been found, at high concentration, to inhibit energy metabolism in mammalian tissue (Manuel & Weiner, 1976;van Rossum, Ernst & Russo, 1981;van Rossum & Russo, 1983). When furosemide (0-5 and 2-0 mmol.1-1) was added to the glucose-free perfusate for the last 40 min of perfusion (gas phase was 02/CO2) no significant effect on ionic contents or adenine nucleotides was observed; e.g.…”