Concanavalin A binding and Ca2+ fluxes in rat spleen cells.

Addition of the mitogenic lectin concanavalin A to rat spleen cells results in a small increase in the steady-state Ca2+ content of the cells. 45Ca2+ fluxes were measured under conditions where artifacts due to Ca2+ binding to concanavalin A could be excluded. Both 45Ca2+ influx into and efflux from these cells are significantly activated by the lectin. If 45Ca2+ is added 30 min after concanavalin A the rate of influx is further enhanced. The increase in 45Ca2+ influx correlates well with binding of concanavalin A to the cells. At low concentrations (optimal mitogenic) of the lectin (1 and 3 micrograms/ml) no significant increase in 45Ca2+ influx occurs but an increase in 45Ca2+ efflux is still observed. The results suggest that concanavalin A binding to the cell surface causes an increase in Ca2+ influx into the cells and that activation of Ca2+ efflux occurs as a response to an increase in the cytosolic Ca2+ activity. Thus, Ca2+ may well play a role in triggering lymphocyte activation.