Light and electron microscopic study of changes in the organization of the cortical actin cytoskeleton during...

Chromaffin cells cultured for 2 days were incubated in the absence or presence of 10 microM nicotine for 40 sec. Resting and stimulated cells were fixed and either prepared for fluorescence microscopy or treated with Triton X-100 to obtain cytoskeletons for ultrastructural studies. Electron microscopy of cytoskeletons revealed the presence of polygonal areas devoid of actin filaments only in nicotinic receptor-stimulated cells. Staining of these cytoskeleton preparations with rhodamine-phalloidin, a probe for filamentous actin, produced fluorescent patterns and three-dimensional images similar to those obtained from resting or stimulated intact cells prepared directly for fluorescence microscopy. Moreover, the percentage of stimulated cells showing disrupted cytoskeleton at the electron microscopic level was similar to the percentage of stimulated cells showing patched rhodamine fluorescence at the fluorescence microscopic level. In addition, cells stimulated with nicotine for 40 sec showed a fivefold increase in amine output and a significant decrease in F-actin levels. These results provide the first ultrastructural evidence for nicotinic receptor-evoked chromaffin cell F-actin disassembly and show that the rhodamine-phalloidin-unstained areas observed in fluorescence microscopy represent the areas devoid of filamentous actin observed at the electron microscopic level.