A role for calcium-activated calmodulin in murine nonspecific cell-mediated cytotoxicity

The role of Ca++ in mouse nonspecific cell-mediated cytotoxicity was studied using the calcium ionophore A23187, inhibitors of calmodulin activity, and agents which modulate cyclic AMP concentration. A23187 markedly enhanced spleen lymphocyte cytotoxicity against SV3T3 target cells, suggesting that Ca++ influx enhances cytolytic activity. This conclusion was supported by experiments in which verapamil, a Ca++ channel blocker, inhibited normal and ionophore-induced cytotoxicity. A23187 also enhanced cytolysis of YAC-1 cells in a 16-hr 51Cr release assay, but had little effect in the more typical 4-hr assay. Lysis of BHK, a cell line resistant to murine natural cytotoxicity, could not be induced by A23187. However, hamster effector cells, which can lyse xenogeneic target cells, showed increased against either SV3T3 or BHK. This indicates that the effect of the ionophore was not due to nonspecific release of toxic products from the effector cells. Both normal and ionophore-enhanced lysis were also inhibited by the phenothiazines chlorpromazine and trifluoperazine, which block the activity of calmodulin. A more specific calmodulin activity inhibitor, W13, was also shown to profoundly inhibit cytotoxicity induced by A23187. These results suggest that Ca++ acts as a stimulus-response coupler in cell-mediated cytotoxicity, and that calmodulin mediates the effects of the Ca++. Furthermore, cyclic AMP appears to modulate the action of Ca++ since agents which increase cAMP levels reduce the effects of A23187.