Uptake of thyroxine in cultured anterior pituitary cells of euthyroid rats.
The uptake of [125I]T4 was investigated in cultured anterior pituitary cells isolated from adult fed Wistar rats and cultured for 3 days in medium containing 10% fetal calf serum. Experiments were performed with [125I]T4 (10(5) to 2 x 10(6) cpm; 0.35-7 nM) in medium containing 0.5% or 0.1% BSA. The uptake of [125I]T4 increased with time and showed equilibrium after around 1 h of incubation. The presence of 10 microM unlabeled T4 during incubation decreased the uptake of [125I]T4 by 65-70% at all time intervals. After 24 h of incubation, 1.5% iodide and 3.2% conjugates were detected in the medium, whereas around 20% of cellular radioactivity represented [125I]T3. The 15-min uptake of [125I]T4 was significantly reduced by simultaneous incubation with 100 nM T4 (by 24%; P < 0.05), 100 nM T3 (by 38%; P < 0.001), or 10 microM rT3 (by 32%; P < 0.001), whereas 10 microM tetraiodothyroacetic acid (Tetrac) had no effect. Furthermore, preincubation (30 min) and incubation (15 min) with 10 microM monodansylcadaverine, oligomycin, or monensin reduced the uptake of [125I]T4 by 30%, 50%, and 40%, respectively (all P < 0.001). Substitution of Na+ in the buffer by K+ diminished the uptake of [125I]T4 by 39% (P < 0.005); 2 mM phenylalanine, tyrosine, or tryptophan reduced [125I]T4 uptake by 18% (P < 0.05), 18% (P = NS), and 33% (P < 0.005), respectively. Our data suggest that the pituitary contains a specific carrier-mediated energy-requiring mechanism for [125I]T4 uptake that is partly dependent on the Na+ gradient. In addition, part of [125I]T4 uptake in the pituitary might occur through an amino acid transport system. When expressed per pM of free hormone, the 15-min uptake of [125I]T4 was approximately as high as that of [125I]T3. Because the reduction of [125I]T4 uptake by T4, T3, monodansylcadaverine, oligomycin, and monensin was roughly the same as the previously reported reduction of [125I]T3 uptake by the same compounds, it is further suggested that T4 and T3 share a common carrier in cultured anterior pituitary cells.
Everts
M E
ME
Department of Internal and Nuclear Medicine, Erasmus University Medical School, Rotterdam, The Netherlands.
Docter
R
R
Moerings
E P
EP
van Koetsveld
P M
PM
Visser
T J
TJ
de Jong
M
M
Krenning
E P
EP
Hennemann
G
G
D000818:Animals; D001667:Binding, Competitive; D002103:Cadaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008985:Monensin / Q000494:pharmacology; D009840:Oligomycins / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D013974:Thyroxine / Q000031:analogs & derivatives / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism; D014285:Triiodothyronine, Reverse / Q000378:metabolism
D007457:Iodine Radioisotopes; D009840:Oligomycins; D014284:Triiodothyronine; D012710:Serum Albumin, Bovine; D014285:Triiodothyronine, Reverse; D008985:Monensin; C008542:monodansylcadaverine; D002103:Cadaverine; C011126:tetraiodothyroacetic acid; D013974:Thyroxine