Two episodes of calcium uptake associated with T-lymphocyte activation

The hypothesis that prolonged mitogenic exposure, such as that required for maximal proliferative stimulation of lymphocytes, induces a similarly prolonged uptake of extracellular calcium was tested on rabbit peripheral T cells by examining the effects of varied lectin dose and duration on calcium accumulation. Concanavalin A stimulation of peripheral T cells was accompanied by two lengthy episodes of calcium accumulation. The first episode was dependent on the presence and concentration of lectin. Sub- and supraoptimal dosages of lectin which are nonmitogenic produced sub- and supraoptimal calcium accumulation profiles suggesting that for optimal cellular stimulation the cellular calcium levels must fall within certain thresholds. The second episode of calcium accumulation occurred at a time when the continued presence of lectin is no longer required for stimulation but the uptake of growth factors is essential. The second episode of calcium uptake was unaffected by lectin dosage and only moderately affected by the duration of lectin exposure. Both episodes of calcium uptake as well as cellular proliferation indices were inhibitable by the calcium channel antagonists verapamil and nifedipine.