The phenothiazine derivatives, fluphenazine and trifluoperazine which are known to bind to calmodulin and to inhibit its activity, abrogate the development of both spontaneous and interferon-enhanced cytotoxicity of mouse splenic lymphocytes enriched for NK cell activity. Phenothiazines also inhibit the rapid increase in cyclic GMP levels in interferon-treated splenic lymphocytes. Furthermore, treatment of mouse splenic lymphocytes with electrophoretically pure interferon, alpha/beta caused a marked decrease in the level of calmodulin within 1 to 4 hours. These results provide evidence that calmodulin may play a role in the development of NK cell cytotoxicity and that the effect of interferon on calmodulin may constitute part of the molecular mechanism of interferon action.
