Influence of extracellular calcium on cell permeabilization and growth regulation by the lymphokine leukoregulin

Permeablization of human K562 leukemia cells was measured in the presence and absence of extracellular ionic calcium to examine the relationship of ionic calcium to increased membrane permeability and the inhibition of cell proliferation by this lymphokine. In the absence of extracellular calcium, the ability of leukoregulin to permeabilize the cell membrane is diminished but is fully restored by addition of 1 mM extracellular Ca++ as shown flow cytometrically by loss of intracellular fluorescein. Membrane permeability is also increased by calcium ionophore A23187 but permeablization is completely blocked in calcium-free medium despite the intramembrane presence of the calcium ionophore. Membrane permeablization by the lectin phytohemagglutinin, in contrast, is independent of extracellular calcium. A similar divergence in cell proliferation activity of the three modulators of calcium flux and membrane permeability occurs in the absence of extracellular calcium. Leukoregulin inhibition of cell proliferation is abolished, inhibition by calcium ionophore A23817 is greatly reduced, and inhibition by phytohemagglutinin is unchanged. Leukoregulin permeabilized K562 cells isolated by fluorescence activated cell sorting resume proliferation after 72 h. In contrast cells permeablized by calcium ionophore A23187 or phytohemagglutinin fail to resume proliferation by 7 days. The membrane permeablizing action of leukoregulin is, therefore, partially dependent upon extracellular calcium. It is also effected through a mechanism other than calcium ionophore transport or lectin type transmembrane signaling, and is accompanied by a reversible inhibition of cell proliferation.