Cytophotometry

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Cytophotometry

 

a method in quantitative cytochemistry used to determine the chemical composition of cells in a histological preparation on the basis of the absorption of light by cells.

In cytophotometry, a beam of monochromatic radiation (light) is passed through the histological preparation, the diameter of the beam being commensurate with the diameter of the cell or the cell structure. The concentration of the substance examined in the cell is found in accordance with the Bouguer-Lambert-Beer law: I = I0eKel, where I is the intensity of the light after passage through the cell, I0 is the intensity of the light incident on the cell, k is the specific monochromatic absorption coefficient of the substance under study calculated per unit of its concentration at a given wavelength of light, and I is the length of the path traversed by the light in the cell (in practical terms, the thickness of the histological preparation). After determining the concentration of the substance within the cell and measuring the volume of the cell, it is possible to calculate the total amount of the substance in the cell.

Cytophotometry was developed by the Swedish histologist T. Casperson in 1936. The sensitivity of the method is on the order of 10–12g. The accuracy of cytophotometry is reduced by measurement errors resulting from the unequal distribution of the substance in the cell; this error can be avoided through cytophotometry at two different emission wavelengths. Ultraviolet cytophotometry makes it possible to determine the quantity of nucleotides, nucleic acids, and proteins in unstained preparations according to their natural absorption of ultraviolet rays.

Cytophotometry is generally used in the visible region of the spectrum; it also makes use of the natural color of individual substances or, more often, the artificial staining of preparations with special histochemical dyes, which combine with the chemical components of the cell in determined quantities. The majority of dyes aid in determining nucleic acids and proteins and their individual reactive groups in the cell and in ascertaining the activity of many enzymes.

REFERENCES

Brodskii, V. Ia. Trofika kletki. Moscow, 1966.
Vvedenie v kolichestvennuiu tsitokhimiiu. Moscow, 1969. (Translated from English.)
Casperson, T. Cell Growth and Cell Function. New York, 1950.

L. Z. PEVZNER