The effect of A23187 upon calcium metabolism in the human lymphocyte.

Treatment of human peripheral lymphocytes with mitogenic concentrations of the divalent cation ionophore A23187 led to an initial marked increase in the uptake of calcium by these cells, but the amount of accumulated calcium retained decreased with time so that after 8-12 h of culture, the calcium content of treated cells was only 1.5-2.0-fold higher than that of control cells. Three possible explanations for the biphasic nature of ionophore-induced calcium uptake were considered: (1) the ionophore underwent chemical or metabolic inactivation upon prolonged incubation; (2) massive accumulation of calcium caused irreversible uncoupling of mitochondria in these cells with consequent loss of accumulated calcium; or (3) with time there was a redistribution of ionophore within the cell, and sufficient ionophore was taken up by internal, most likely mitochondrial, membranes to cause an efflux of calcium from internal stores. By developing a bioassay for ionophore and examining the time-dependent effects of ionophore in the presence and absence of calcium, it was concluded that the third explanation was the most likely. The general implications of these results are discussed.