Cytochalasin binding to macrophages

Abstract

Cytochalasin-sensitive structures are involved in macrophage motility, membrane recognition phenomena and the internalization of phagocytic particles. The purpose of this study was to characterize the binding of cytochalasins to rabbit alveolar macrophages. Kinetic and quantitative binding experiments demonstrated rapid, temperature dependent attachment of [3H]CB (tritium labeled cytochalasin B) to high (0.4 M) and low (10 M) affinity sites. Macrophages possessed a larger number of high affinity sites (1.8 × 107 sites/cell) than erythrocytes, lymphocytes, granulocytes, and other cell types so far examined. CB was the best inhibitor of high affinity [3H] CB binding, although CA, CD, and CE were also highly effective. However, cytochalasins A, E, and D were considerably more potent inhibitors of low affinity [3H] CB binding sites than CB. In contrast to cytochalasins A and E, CB binding was easily reversible, while cytochalasin D binding was partially reversible. A wide variety of pharmacologic agents, including cyclic nucleotides and sulfhydryl containing or reactive compounds, had minimal inhibitory or no effect on either low or high affinity cytochalasin binding to intact cells. Vinblastine but not colchicine augmented [3H] CB binding. Radioautography demonstrated that most of the high affinity [3H] CB binding sites appeared to be located in or adjacent to the plasma membrane. The previously described alterations in macrophage function induced by cytochalasins required relatively high concentrations and our data suggest that low affinity sites would be primarily involved in mediating these changes.