Ca2+ translocation in Ehrlich ascites tumor cells

Abstract

Ca²⁺ uptake into Ehrlich ascites tumor cells was studied at 0°C in the presence of mitochondrial inhibitors, conditions that minimized complications caused by sequestration of Ca²⁺ into organelles or by excretion. Under these conditions Ruthenium Red inhibited Ca²⁺ uptake, but other previously implicated ions, such as P_i or Mg²⁺, had no effect. Valinomycin either inhibited or slightly stimulated Ca²⁺ uptake depending on the presence of excess K⁺ on the outside or inside of the cell, respectively. Nigericin inhibited Ca²⁺ transport. Based on these data we propose an electrogenic uptake of Ca²⁺, possibly via a Ca²⁺/H⁺ antiport mechanism. The observation that glucose inhibited Ca²⁺ uptake suggested that in Ehrlich ascites tumor cells an energy-driven Ca²⁺ expulsion mechanism is operative, similar to that in erythrocytes. Plasma membrane preparations of ascites tumor cells were found to contain a Ca²⁺-dependent ATPase. These preparations, when incorporated into liposomes in an inside-out orientation, catalyzed an ATP-dependent uptake of Ca²⁺.