Quarterly Journal of Microscopical Science, Vol s3-106, 299-306, Copyright © 1965 by Company of Biologists

A further note on the measurement of the affinity of a dye (Azure A) for histological substrates

¹ Department of Anatomy, University of the Witwatersrand Medical School, Johannesburg

If two histological sections, of thickness nµ and 2nµ, and having the same apparent intensity of staining, are at equilibrium with dyebaths of concentration B₁ and B₂ respectively, the affinity of the histological substrate for the dye is, under denned conditions, given by the expression F° = - RT In I/B, where B is either (i) B₂ if the thinner section is stained to saturation, or (ii) B₁ if B₁ = ₃B₂. The affinity tends to be greater when measured in a weaker dyebath, as implied in method (ii).

Evidence is presented suggesting that the uptake of the basic dye Azure A by pancreatic basal chromidial substance, goblet cell mucin and intestinal epithelial cytoplasm follows a Langmuir adsorption isotherm to a first approximation, in that, at low dyebath concentrations, the uptake of dye is proportional to the concentration of dyebath with which the substrate is in equilibrium, while in strong dyebaths the uptake approaches a plateau. A deviation from the ideal Langmuir isotherm in dyebaths of moderate concentration, observed in epithelial cytoplasm and to a lesser extent in pancreatic basal chromidial substance, may have been due to interaction between neighbouring dye-binding sites, or to the presence in a single area of sites with different affinities for the dye.

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Department of Human Biology and Anatomy, The University, Sheffield 10.