Perturbation of the phagocytic response in P388D1 cultured macrophages by agents altering cell calcium

Phagocytosis in adherent P388D₁ (D₁) cells was monitored utilizing formalin treated $\text{Listeria}$$\text{monocytogenes}$ ($\text{Lm}$) previously labeled with ¹²⁵iododeoxyuridine. The dependence of this phagocytic process on calcium was studied by using several agents which alter calcium metabolism. The calcium antagonist ruthenium red (RR) produced a dose and time dependent stimulation (60–70%) of $\text{Lm}$ phagocytosis by D₁ cells. Utilizing another calcium antagonist, D-600, a prolonged inhibition (4 hours) of phagocytosis (40%) was observed. The addition of the cation ionophore A23187 produced a transient stimulatory increase (38% at 2 hours) in the phagocytic response. The concomitant addition of RR and D-600 did not alter the phagocytosis of $\text{Lm}$ by D₁ cells as compared to control cells. However, this complete drug/drug antagonism was not seen with the combinations of A23187 and D-600 or RR and A23187. The addition of A23187 and D-600 resulted in a time dependent inhibition of phagocytosis which did not become maximal until 3 to 4 hours. A23187 and RR produced a time independent stimulation of phagocytosis which was significantly less than that which was observed for RR alone, but was of longer duration than the response produced by A23187 alone. The use of these calcium probes in the P388D₁ macrophage model suggests a role for calcium in the phagocytic process.