Role of ions in activation of human lymphocytes

Phytohemagglutinin (PHA)-stimulated lymphocytes were cultured in media containing varying levels of K+, Mg2+, Ca2+. Cell activation was monitored by measuring nuclear diameter and by evaluating the area of nucleolus which reacted with silver nitrate. Decreasing extracellular K+ from normal levels (5.0 mM) to 14% (0.7 mM) and decreasing extracellular Mg2+ from normal levels (1.0 mM) to 14% (0.14 mM) did not affect nuclear diameter or silver nitrate reactivity of PHA-stimulated lymphocytes. Chelation of extracellular Ca2+ with EGTA during the first 24 h after PHA stimulation completely inhibited the increases in silver reactivity and nuclear diameter associated with stimulation. Chelation of extracellular Ca2+ 48 h after PHA stimulation did not inhibit lymphocyte stimulation. Inhibitory effects of EGTA were completely reversed if CaCl2 was added to the medium within 24 h of PHA stimulation. By 48 h the effects were irreversible.