Accelerated calcium ion uptake in murine thymocytes induced by concanavalin A

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 V_max. Uptake of the anion, CrO₄^2–, 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.