Stimulation of Sugar Transport in Cultured Heart Cells by Triiodothyronine (T₃) Covalently Bound to Red Blood Cells and by T₃in the Presence of Serum^*

Abstract

T3, covalently bound to red blood cells (RBCs), stimulated the uptake rate of 2-deoxy-D-glucose (2-DOG) in cultured chick embryo heart cells. The response, measured 6 h after exposure, was at least the same than that to free T3. An inhibitor of rhodamine-T3 internalization, bacitracin, did not affect the stimulation of sugar uptake by T3 regardless of whether T3 was covalently bound or free. Pretreatment of RBC-T3 with anti-T3 immunoglobulin G completely blocked the effect of T3, whereas normal rabbit immunoglobulin G failed to do so. Addition of 5% chick serum to the medium stimulated 2-DOG uptake to 144% of the control at 6 h. Adding T3 (10 nM) to the serum-containing medium increased 2-DOG uptake to 171% of the control. The effect of T3 alone or in the presence of serum was not inhibited by cycloheximide, puromycin, or actinomycin D. A T3 dose response curve, in medium containing 10% dehormonized serum, showed enhancement of the T3 effect when compared with the curve obtained in the serum-free medium. The minimal effective concentration of T3 was 10 pM in the presence of serum and 100 pM in its absence. The slope of the linear portion of the dose response curve was greatly increased and the maximal response markedly enhanced by serum. The ED50 was 0.33 nM vs. 0.43 nM in terms of total T3 concentration and 0.16 nM vs. 0.43 nM in terms of free T3 in the presence or absence of serum, respectively. These data suggest that T3, in physiological concentrations, activates sugar transport through an external contact with the cell surface.

3,5,3′ Triiodo-L-thyronine Stimulates 2-Deoxy-D-Glucose Transport into L6 Muscle Cells Through the Phosphorylation of Insulin Receptorβand the Activation of PI-3k

“…In this case, T 3 was not available for entry into the cells and therefore we suggested that it probably interacted with sites on the plasma membrane (8). In order to clarify this point further, we prepared a monoclonal T 3 -anti-idiotypic antibody that displaced T 3 in a radioimmunoassay.…”

“…The stimulation of 2-DOG uptake by T 3 -RBC was completely blocked by rabbit anti-T 3 immunoglobulin G (IgG), whereas normal rabbit IgG failed to block. Most probably, T 3 -RBC stimulated 2-DOG uptake in these cells by an interaction with the plasma membrane (8). Furthermore, we produced a T 3 anti-idiotypic monoclonal antibody that stimulated the uptake of 2-DOG uptake in cardiomyocytes in a manner similar to T 3 -RBC.…”

T3 stimulation of 2-deoxy-D-glucose uptake in cultured chick embryo carcass derived cells, requires neosynthesis of proteins

“…This effect, which occurred with¬ in the first 6 h of exposure to physiological concentrations of the hormone, was not suppres¬ sed by actinomycin-D, cycloheximide or puromycin and could be elicited even when the T3 was presented while covalently bound to erythrocytes (Dickstein et al 1983). These data suggest that the plasma membrane in cardiomyocytes is a target for a direct action of thyroid hormones.…”

“…In previous publications (Segal & Gordon 1977a,b;Segal et al 1977;Dickstein et al 1983;Gordon et al 1986), it was shown that T3 stimu¬ lates sugar transport into cultured chick embryo cardiomyocytes. This effect, which occurred with¬ in the first 6 h of exposure to physiological concentrations of the hormone, was not suppres¬ sed by actinomycin-D, cycloheximide or puromycin and could be elicited even when the T3 was presented while covalently bound to erythrocytes (Dickstein et al 1983).…”

The Production of a Monoclonal T3-Antiidiotypic Antibody (T3-MAAB) That Mimics the Effects of T3on 2-Deoxy-D-glucose Uptake in Chick Embryo Heart Cells

“…Furthermore, we have shown that when cells were exposed to T3 covalently bound to WE have previously shown that T3 stimulates the uptake RBC (T3-RBC) only the early plasma membrane phase was of 2-deoxy-D-glucose into cultured chick embryo heart observed (3). These data led us to suggest that T3, at an early cells (1).…”