Calcium ion influx during mitogenic stimulation of lymphocytes.

The uptake of free calcium ion (Ca2+) in PHA- or A23187-stimulated lymphocytes was measured using 45CaCl2 and 3H-water. Augmentation of Ca2+ uptake by both mitogens was observed, but the enhanced uptake occurred transiently, sometime within 30 min of the stimulation. The total amount of calcium in quiescent lymphocytes as determined by atomic absorption spectroscopy was about 2.9 X 10(-15) g/cell. When stimulated with PHA, more calcium gradually accumulated in the cells. The maximum amount of accumulation occurred at around 40 h, and was about 2-fold higher than that of control cells. In A23187-stimulated cells, the calcium content increased within 1 h by about 4-fold, reached a maximum at about 6 h (6-fold) and thereafter, surplus calcium was pumped out. The cytosolic free calcium ion concentration (the [Ca2+]i) within single cells was measured using quin 2 or fura-2. The [Ca2+]i was about 1 X 10(-7) M, and a transient increase in the [Ca2+]i was observed in some cells within 1 min after Con A-stimulation. Another rise in the [Ca2+]i was observed around the 40th h, and the maximum expression of the IL-2 receptor was observed at about this time. Therefore the results may indicate that the IL-2-mediated lymphocyte transformation is dependent on the rise in the [Ca2+]i.