Net Movements of Calcium and Magnesium in Slices of Rat Liver

Rat liver slices incubated at 1 degrees C in phosphate (10 mM) or bicarbonate (25 mM) plus phosphate (2 mM)-buffered Ringer's solutions containing 1.2 mM Ca(2+) underwent a 3-fold increase in Ca(2+) content relative to their fat-free solids, and lost 10% of their Mg(2+). Upon subsequent incubation at 38 degrees C, slices in the bicarbonate medium lost about half of the accumulated Ca(2+). This extrusion was less efficient in the phosphate medium. Succinate (40 mM), which strongly stimulated respiration, caused an accumulation of Ca(2+) in slices incubated in the phosphate medium. The extrusion of Ca(2+) 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(2+) transport was itself directly dependent on high-energy compounds and was not due to a hetero-exchange diffusion of Ca(2+) against Na(+) ions. Some evidence was obtained for the occurrence of an active accumulation of Mg(+) ions.