Thyroid hormone action on glucose transporter activity in astrocytes

In astrocytes from rat brain cultured in thyroid hormone-deficient media cytochalasin B-binding was decreased 80%; addition of L-T3 increased binding to 75% of control levels. Saponin-treatment of controls increased accessibility of binding sites to 60% above untreated cells. Saponin also increased binding in deficient cells; however, the level was less than in treated controls, suggesting L-T3 deficiency decreases total glucose transporters. Addition of L-T3 appeared to convert most (90%) of the binding sites from unavailable to accessible status. Changes in binding to plasma membranes in response to L-T3 level were similar to those in intact cells. No binding to Golgi was detectable, thus no evidence for translocation of carriers was obtained. L-T3 may activate the glucose transporter by increasing its accessibility in brain cells.