Distribution of sodium, magnesium, phosphorus, sulphur, chlorine, potassium, calcium and iodine in mammalian thyroid gland.

Anhydrous specimen preparation techniques and X-ray microanalysis were used to study the elemental composition of the rat thyroid follicular cells and colloid in the follicular lumen. Analysis were performed in morphologically defined follicular cells and adjacent colloid. Use of semithin cryosections allowed us to selectively analyze cell nucleus and dense vesicles in the cytoplasm of follicular cells. The analytical results indicate that the basolateral and apical cell membrane of follicular cells act differently in the transport of iodine and other ions, thus creating ionic gradient in the follicular lumen as compared to that found in the follicular cells. High potassium levels were found in the colloid. This finding indicates an active secretion of potassium from the apical plasma membrane into the follicular lumen. High sulphur and calcium levels were also found in the colloid. Dense vesicles found in the cytoplasm of follicular cells varied in size and had different elemental composition.