Accelerated calcium ion uptake in murine thymocytes induced by concanavalin A

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Abstract
The mechanism of enhancement of Ca2+ uptake by the T cell mitogen concanavalin A (Con A) was studied in murine thymocytes. Native Con A enhanced the rate of Ca2+ uptake as much as 9‐fold, an increase being observed within five minutes after Con A addition. The effect of Con A was reversed completely by α‐methyl mannopyranoside (α‐MM). Increased Ca2+ uptake was observed with increasing concentrations of Con A, between 2 and 400 μg/ml, indicating that the stimulation of Ca2+ uptake is not restricted to mitogenic lectin concentrations (0.5‐2 μg/ml). Succinyl Con A exhibits only a slight effect in the same concentration ranges as native Con A. Ca2+ uptake, both in the absence and presence of Con A, is strongly dependent on energy metabolism and is carrier mediated. The augmentation of Ca2+ uptake by native Con A is due to an enhanced Vmax. Uptake of the anion, CrO42–, by thymocytes, found to be a nonsaturable process, was also enhanced by Con A. The effect of Con A on CrO42− permeability appears to be independent of its effect on Ca2+ uptake.