Electron Microscopic Studies on Macrophages II. Effect of Colchicine and Cytochalasin B on the Cell Cortex as Revealed by Ultrathin Sectioning

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Abstract
We have examined mouse peritoneal macrophages which were treated with colchicine and cytochalasin B for 6 hr from the beginning of a culture by ultra-thin sectioning in an attempt to reveal the Internal organizations with special reference to microfilaments and microtubules. In control macrophages, the cell cortex including small processes on the dorsal surface and extending pseudopodia was composed of a microfllamentous network. The colchicine treatment affected the cell cortex; thin pseudopodia extended much more and smaller processes were produced as compared with control macrophages, but the normal movements of mitochondria, lysosomes and other cytoplasmic organelles to the periphery of the cell were suppressed. Microtubules were not observed. The colchicine-induced pseudopodia and the small processes were composed of the same filamentous network as control macrophages. The cytochalasin B treatment also affected the cell cortex; however, thin pseudopodia and small processes were scarcely produced, and the filamentous network which was usually observed in the cell cortex was located in the zone beneath the surface attached to a substratum of the cell in where numerous vacuoles were gathered. Our observations suggest that the flattening of the cell body (the translocation of cytoplasmic organelles and the nucleus) is associated with the function of microtubules, and the movement and localization of the cortex composed of microfllamentous network were sensitive to cytochalasin B.