Astrocytes are glial cells with a diverse set of functions; among others they are involved in integrating neuronal functions, and in the maintenance of the blood brain barrier. There is a close relationship between the endocrine system and the central nervous system (CNS). Thyroid hormones (THs) are an important factor in the development and function of the CNS. Thyroid follicular cells secrete mainly the hormone T4 (and to a lesser extent the hormone T3), which enters the CNS via the bloodstream. Its transfer across the blood-brain barrier into astrocytes is facilitated by specialized transporters, including L-type amino acid transporters (LATs). Within astrocytes, the hormone T4 is converted by the enzyme deiodinase type 2 into the active form of T3, which is secreted into the intercellular space through the before mentioned transporters, including through LAT2. The impact of TH imbalance on synaptic transmission and plasticity is known, however, it is unclear how astrocytes contribute to the development of neuropsychological disorders. Here we investigated the effect of elevated concentrations of T3 hormone on the redistribution of the LAT2 transporters in astrocytes, on the mobility of endocytic vesicles, on calcium ion concentration in astrocytes, and on the structure of the cytoskeleton. Long-term exposure to elevated concentrations of the hormone T3 was shown to reduce the proportion of the LAT2 transporter in the plasmalemma. Accordingly, the velocity of endocytic vesicles carrying LAT2 transporter increased with prolonged exposure to elevated concentrations of the hormone T3. In addition, we observed an increase in the concentration of calcium ions. Finally, prolonged exposure to elevated T3 hormone concentrations also resulted in a slight depolymerization of α-tubulin.
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