Kinetics of long‐term (72 hr) calcium content during mitogen activation of cultured human T lymphocytes

In vitro stimulation of human blood lymphocytes with mitogen resulted in an increased intracellular content of Ca 2+ per unit cell volume. This increase in Ca 2+ content of lectin‐activated cells reached a maximum after 24 hr of culture and thereafter slowly declined. Brief treatment of cells at 24 hr of culture with the Ca 2+ ionophore A23187 in combination with EGTA resulted in a larger release of Ca 2+ from cells in mitogen‐stimulated cultures than from cells in control cultures. This indicates that the Ca 2+ is accumulated intracellularly but is readily exchangeable. At 24 hr of culture the increase in cellular Ca 2+ correlated well with the proliferative response as measured by 3 H‐thymidine incorporation. Ca 2+ influx at 24 and 48 hr of culture was markedly enhanced in the mitogenically stimulated cells as compared either to cells cultured for 1 and 72 hr or cells cultured without mitogen.