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.

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