Net Movements of Calcium and Magnesium in Slices of Rat Liver

Rat liver slices incubated at 1°C in phosphate (10 mM) or bicarbonate (25 mM) plus phosphate (2 mM)—buffered Ringer's solutions containing 1.2 mM Ca²⁺ underwent a 3-fold increase in Ca²⁺ content relative to their fat-free solids, and lost 10% of their Mg²⁺. Upon subsequent incubation at 38°C, slices in the bicarbonate medium lost about half of the accumulated Ca²⁺. This extrusion was less efficient in the phosphate medium. Succinate (40 mM), which strongly stimulated respiration, caused an accumulation of Ca²⁺ in slices incubated in the phosphate medium. The extrusion of Ca²⁺ 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 Ca²⁺ transport was itself directly dependent on high-energy compounds and was not due to a hetero-exchange diffusion of Ca²⁺ against Na⁺ ions. Some evidence was obtained for the occurrence of an active accumulation of Mg⁺ ions.