The net extrusion of calcium and its temporal relation to the accumulation of potassium in slices of rat liver and of Morris hepatomata 5123tc and 3924A.

slices showed an extrusion of 5 mmoles calcium per kg dry weight that was completed after 6 min, while potassium accumulation showed a lag period of about 15 min. Similar results were obtained from livers of rats of different strains and from livers of goose, opossum, and baboon. Slices of 5123tc extruded 16 mmoles calcium per kg dry weight during about 10 min, the initial rate being about five times that seen in liver; potassium accumulation was first observed after a delay of 6 min. Slices of 3924A extruded similar amounts of calcium at an initial rate similar to that of slices of 5123tc, but the final level of calcium remained higher; this is attributed to retention of calcium in micronecrotic areas of the slices of 3924A. This tumor also showed a lag period before potassium accumulation, although of only a 3-min duration. The calcium-transporting activity of the tumors is discussed in relation to their calcium content in vivo and to the possible effects of intracellular calcium in controlling cellular permeability to potassium.