Differential basophilia of adrenomedullary catecholamine storing granules induced by glutaraldehyde fixation

Summary

Adrenomedullary A and NA cells cannot be distinguished on the basis of staining intensity with metachromatic cationic dyes after formol fixation. The metachromatic tendency of both A and NA granules in the formol fixed adrenal medulla is the expression of sufficient anionic charge density in the carboxyl rich protein of CAM granules to allow dye-dye interactions. The orthochromatic color of glutaraldehyde fixed NA granules is not simply the consequence of inadequate surface charge density in the chromotrope but rather of a different dye-substrate interaction. This interaction cannot be broken by high ionic strength and cannot be operpowered by metachromasia inducing inorganic compounds like K₃Fe(CN)₆ or KJ. Changes in the absorption spectra of a model dye-substrate system and of spontaneous dye-dye interaction caused by noradrenaline suggests that the orthochromatic property of the chromotrope in glutaraldehyde fixed NA granules is imparted by the reaction product of noradrenaline. The lone pair electrons of the amine nitrogen of dye molecules can be assumed to be involved in a donor-acceptor complex with the reaction product of noradrenaline which is likely to prevent charge transfer interactions between the neighbouring dye molecules.