Freeze-etching observations on the characteristic arrangement of intramembranous particles in the apical plasma membrane of the thyroid follicular cell in TSH-treated mice

Thyroid glands of normal, TSH-treated and Thyradin (powdered thyroid)-treated mice were examined by means of the freeze-etching method. Intramembranous particles on the PF (= A face) face of the apical plasma membrane often form aggregates especially in TSH-treated mice. Each aggregate, about 200 nm in diameter, and consisting of 15–25 large particles, corresponds to a depression of the apical cytoplasm, and the particles sometimes form rosettes. Particle-aggregates are very rare in the apical plasma membrane of the thyroid follicular cell of the Thyradin-treated animal. In the cytoplasm just beneath the particle-aggregate no secretory granules, reabsorbed colloid droplets or other special structures are found.