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| Content Provider | PubMed Central |
|---|---|
| Author | Docter, Roelof Krenning, Eric P. Bos, Greetje Fekkes, Durk F. Hennemann, George |
| Abstract | We investigated 3,3′,5-tri-iodo-l-thyronine transport by human erythrocytes and by `ghosts' prepared from these cells. Uptake of tri-iodothyronine by erythrocytes at 37°C was time-dependent with a maximum reached after 60min. Tracer analysis after incubation for 1min revealed only one saturable binding site, with K m 128±19nm (mean±s.e.m.; n=7) and V max. 4.6±0.7pmol of tri-iodothyronine/min per 6×107 cells. After 10min incubation K m 100±16nm (n=10) was found with V max. 7.7±1.2pmol of tri-iodothyronine/10min per 6×107 cells. At 0°C the uptake system is still active, with K m 132±26nm and V max. 1.8±0.3pmol of tri-iodothyronine/10min per 6×107 cells. The V max. with intact cells is 5-fold greater than the V max. with membranes derived from the same amount of cells when uptake studies are performed in media with similar free tri-iodothyronine concentrations. This indicates that at least 80% of tri-iodothyronine taken up by the intact erythrocytes enters the cell. This saturable uptake system can be inhibited by X-ray-contrast agents in a dose-dependent fashion. (±)-Propranolol, but not atenolol, has the same effect, indicating that the membrane-stabilizing properties of (±)-propranolol are involved. Furthermore, there is no inhibition by ouabain or vanadate, which indicates that tri-iodothyronine uptake is not dependent on the activity of Na++K+-dependent adenosine triphosphatase. We have prepared erythrocyte `ghosts', resealed after 2.5min with 0mm-, 2mm- or 4mm-ATP inside. Inclusion of ATP and integrity of the membrane of the erythrocyte `ghosts' were verified on the basis of an ATP-concentration-dependent functioning of the Ca2+ pump. No difference was found in the uptake of tri-iodothyronine by erythrocyte `ghosts' with or without ATP included, indicating that uptake of tri-iodothyronine is not ATP-dependent. The following conclusions are drawn. (1) Tri-iodothyronine enters human erythrocytes. (2) There is only one saturable uptake system present for tri-iodothyronine, which is neither energy (i.e. ATP)-dependent nor influenced by the absence of an Na+ gradient across the plasma membrane. This mode of uptake of tri-iodothyronine by human erythrocytes is in sharp contrast with that of rat hepatocytes, which uptake system is energy-dependent and ouabain-sensitive [Krenning, Docter, Bernard, Visser & Hennemann (1978) FEBS Lett. 91, 113–116; Krenning, Docter, Bernard, Visser & Hennemann (1980) FEBS Lett. 119, 279–282]. (3) X-ray-contrast agents inhibit tri-iodothyronine uptake by erythrocytes in a similar fashion to that by which they inhibit the uptake of tri-iodothyronine by rat hepatocytes [Krenning, Docter, Bernard, Visser & Hennemann (1982) FEBS Lett. 140, 229–233]. |
| Starting Page | 27 |
| File Format | |
| ISSN | 14708728 |
| e-ISSN | 14708728 |
| Journal | Biochemical Journal |
| Issue Number | 1 |
| Volume Number | 208 |
| Language | English |
| Publisher Date | 1982-10-15 |
| Access Restriction | Open |
| Subject Keyword | Research in Higher Education |
| Content Type | Text |
| Resource Type | Article |
| Subject | Cell Biology Molecular Biology Biochemistry |
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