Summary
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1.
The dispersion of dye molecules and small cations injected from a point source in the cytoplasm of molluscan neurons has been measured photometrically and compared with dispersion in aqueous solution.
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2.
The diffusion of phenol red and arsenazo III was at least a factor of five slower in the cytoplasm than in saline. Movement of both dyes was slowed by about the same factor in a given cell. The dispersion rate of arsenazo III was not significantly affected by preloading the cytoplasm to dye concentrations up to 0.5 mM.
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3.
Calcium and barium dispersion was measured in neurons and saline droplets preloaded with arsenazo III, while phenol red absorbance changes were used to follow the dispersion of injected protons. Ba2+ and H+ moved very slowly in the cytoplasm compared to aqueous solution.
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4.
Ca2+ movement in all probability underwent a similar retardation in the neurons but high-affinity buffering of the cytoplasm severely restricted the spread of detectable amounts of this ion away from the injection site.
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Connor, J.A., Ahmed, Z. Diffusion of ions and indicator dyes in neural cytoplasm. Cell Mol Neurobiol 4, 53–66 (1984). https://doi.org/10.1007/BF00710942
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DOI: https://doi.org/10.1007/BF00710942