Real-time dynamics of the F-actin cytoskeleton during secretion from chromaffin cells

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Abstract
Transmitted light images showed an intricate and dynamic cytoplasmic structural network in cultured bovine chromaffin cells observed under high magnification. These structures were sensitive to chemicals altering F-actin-myosin and colocalised with peripheral F-actin, β-actin and myosin II. Interestingly, secretagogues induced a Ca2+-dependent, rapid (>10 second) and transitory (60-second cycle) disassembling of these cortical structures. The simultaneous formation of channel-like structures perpendicular to the plasmalemma conducting vesicles to the cell limits and open spaces devoid of F-actin in the cytoplasm were also observed. Vesicles moved using F-actin pathways and avoided diffusion in open, empty zones. These reorganisations representing F-actin transfer from the cortical barrier to the adjacent cytoplasmic area have been also confirmed by studying fluorescence changes in cells expressing GFP-β-actin. Thus, these data support the function of F-actin-myosin II network acting simultaneously as a barrier and carrier system during secretion, and that transmitted light images could be used as an alternative to fluorescence in the study of cytoskeleton dynamics in neuroendocrine cells.