Elemental concentrations within types 2 and 3 epithelial cells of the rat thymus

The elemental composition (Na, Mg, P, S, Cl, K, Fe and Zn) of epithelial cells of rat thymus cortex has been determined using X-ray microanalysis of freeze-dried frozen sections. The cytoplasm contained highly significantly lower levels of potassium and phosphorus than the nuclei. When the results were compared with a previous study of the elemental levels in cortical thymocytes (using the same material), only differences in the P concentration were found. This is probably attributable to the greater degree of leptochromasia usually observed in epithelial cells compared with thymocytes. Since thymocyte maturation depends very closely on the microenvironment created by the epithelial cells, the great similarity in elemental levels observed in this study could be important in the control of cell division and maturation events.