Ca2+ translocation in Ehrlich ascites tumor cells

Abstract

Ca2+ uptake into Ehrlich ascites tumor cells was studied at 0 degrees 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 Pi 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+.

Control, modulation, and regulation of cell calcium

“…Data obtained with cultured monkey kidney cells incubated in Krebs-Henseleit bicarbonate buffers containing various calcium and phosphate concentrations. Adapted from Bode 1971a This is supported by the finding that in Ehrlich ascites cells the uptake of calcium, which is stimulated by increasing extracellular phosphate, is sensitive to mitochondrial uncouplers (Chartton and I4/enner 1978;Hinnen et al 1979). The increased 4SCa uptake produced by phosphate reflects an enlarged intracellular exchangeable pool and not an increased calcium influx, because at steady state the exchange of calcium across the plasma membrane is reduced by phosphate (Bode and Uchikawa 1978).…”

“…In liver, kidney, and smooth muscle a rise in pH increases, while a low pH decreases, the total cell calcium (Wallach et al 1966;Rorive and Kleinzeller 1972;Van Breemen et al 1973;Studer and Borle 1979). The intracellular exchangeable calcium measured by 4s Ca uptake is also elevated by high pH and depressed at low pH in fibroblasts, lymphocytes, mast cells, smooth muscle, kidney, and Ehrlich ascites cells (Lamb and Lindsay 1971;Whitney and Sutherland 1973;Morgenstern 1972;Foreman et al 1977;Studer and Borle 1979;Hinnen et al 1979). In kidney cells, while acidosis depresses both total calcium and exchangeable calcium proportionately, alkalosis enhances the total calcium much more than the exchangeable calcium and most of the calcium gain is found in an unexchangeable pool, presumably in mitochondria (Studer and Bode 1979).…”

Alterations in intracellular calcium compartmentation following inhibition of calcium efflux from isolated hepatocytes

“…plasma membrane Ca2+ extrusion has been reported to be associated with cellular Ca2+ accumulation also in other experimental systems, e. g. human erythrocytes treated with vanadate [34] or depleted of intracellular ATP [35], and Erlich ascites tumor cells incubated at low temperature [36]. At present, the molecular mechanism by which extracellular ATP inhibits plasma membrane Ca2 + extrusion remains unknown, although it appears that this effect could be part of a more general inhibition of plasma membrane transport ATPases, resulting in the intracellular accumulation of both Ca2 + and Na' [20] (this work).…”

Amiloride inhibits murine erythroleukemia cell differentiation: evidence for a Ca2+ requirement for commitment.

“…Ca2+ Uptake. Ca2+ uptake was measured essentially as described by Hinnen et al (16) except that Chelex 100 (100-200 mesh; Bio-Rad) was used instead of Dowex 5OW, 50 X 8-100. MEL cells were grown for 24 hr at 370C in a medium containing 1.5% Me2SO, 1.5% Me2SO and amiloride (10,ug/ml), or no drug.…”