Calcium Ion Distribution in Cytoplasm Visualized by Aequorin: Diffusion in Cytosol Restricted by Energized Sequestering

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Abstract
The distribution of Ca 2+ in the cytoplasm following a local rise in Ca 2+ concentration is visualized by means of aequorin luminescence and a television system with an image intensifier. Diffusion of Ca 2+ through the cytosol is so constrained that a rise in cytoplasmic Ca 2+ concentration produced by local Ca 2+ entry through cell membrane or by local Ca 2+ injection is confined to the immediate vicinity of these sites. The diffusion constraints are lifted by treatment with cyanide or ruthenium red. Thus, energized calcium sequestering, probably by mitochondria, is the dominant factor in the constraints. In cell regions where the sequestering machinery is sufficiently dense, different Ca 2+ message functions inside a cell may be effectively segregated, permitting private-line intracellular communication.

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