The Role of Microtubules and Microfilaments in Thyroid Secretion

Abstract

This chapter discusses the role of microtubules and microfilaments in thyroid secretion. Microtubules, organized into special structures, are associated with both rapid and slow movement in cells. By contrast, a structural or nonmotile role is likely for microtubules in nervous tissue. To explore the possible role of microtubules in thyroid secretion, microtubules, antitubulins, and the secretory process must be examined. Microtubules are found at very different levels of geometrical organization. Activation of thyroid secretion proceeds by a nonprotein synthetic action of cyclic adenosine 5′-phosphate (cAMP) on the mobility and deformability of the apical membrane of the thyroid cell, which in turn leads to pseudopod formation and endocytosis of colloid droplets. Such surface effects may be akin to those seen in cells in culture exposed to cAMP. These are transformed from the epithelium-like cells to fibroblast-like cells with processes or axon elongation under the influence of nerve growth factor. Colchicine, colcemid, and/or cytochalasin reverse or prevent these elongations and favor the epithelial form. An antagonism between cAMP and colchicine is also observed on cell surface activity.