Augmentation of zinc ion stimulation of lymphoid cells by calcium and lithium

Stimulation of hamster lymph node cells by optimal concentrations of ZnCl₂ (10 μM) was found to be enhanced by addition of 1–25 mM LiCl to the serum-free cultures. Maximal enhancement occurred at 10 mM Li⁺. Similar concentrations of either KCl or NaCl did not potentiate stimulation. Addition of 1 mM CaCl₂, but not 1–25 mM MgCl₂, also potentiated Zn²⁺ stimulation of lymph node cells. When the cultures were supplemented with 1 mM Ca²⁺ + 10 mM Li⁺, a synergistic potentiation of Zn²⁺ stimulation occurred. In addition, the dose response curve for Zn²⁺ was shifted such that maximal stimulation occurred at 100–250 μM Zn²⁺, a concentration of Zn²⁺ which was toxic for the unsupplemented cultures. In Ca²⁺ + Li⁺ supplemented cultures, Zn²⁺ stimulated ³H]thymidine incorporation to levels comparable to those obtained when hamster lymphoid cells were stimulated with lectins. In addition to Zn²⁺ stimulation, Ca²⁺ + Li⁺ supplemented medium also enhanced Hg²⁺ stimulation of hamster lymph node cells but did not change the dose response curve for Hg²⁺. Therefore, the observed ionic effects on Zn²⁺ stimulation of lymphocytes were unique to this mitogen, when compared to either Hg²⁺ stimulation or previously reported lectin stimulation of hamster lymphoid cells.