Cytoplasmic motility reflects phagocytic activity in alveolar macrophages from dog lungs

To determine whether cytoplasmic motility relates to phagocytic activity of alveolar macrophages (AM), we measured the remanent field strength (RFS) from the AM containing Fe₃O₄ particles (5 × 10⁶ cells) and the number of phagocytized fluorescent latex spheres in the AM without having Fe₃O₄ particles (10⁶ cells) harvested by broncho-alveolar lavage from dog lungs in vitro. Cytoplasmic motility was estimated from the relaxation rate (λ_o; min^-1) calculated from the decay curve of RFS and the number of phagocytized latex spheres was counted using fluorescent microscopy after the addition of latex spheres (5 × 10⁷). The tumor necrosis factor increased both λ_o and the number of phagocytized latex spheres, and cytochalasin D and colchicine decreased them in a concentration-dependent fashion. Increases and decreases in λ_o induced by drugs paralleled the number of phagocytized latex spheres. These results suggest that cytoplasmic motility reflects phagocytic activity of AM and both cytoplasmic movement and phagocytosis may be regulated by a similar mechanism in the cytoskeletal system.