These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Evidence that the uptake of tri-iodo-L-thyronine by human erythrocytes is carrier-mediated but not energy-dependent.
    Author: Docter R, Krenning EP, Bos G, Fekkes DF, Hennemann G.
    Journal: Biochem J; 1982 Oct 15; 208(1):27-34. PubMed ID: 7159396.
    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 degrees 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 6x10(7) cells. After 10min incubation K(m) 100+/-16nm (n=10) was found with V(max.) 7.7+/-1.2pmol of tri-iodothyronine/10min per 6x10(7) cells. At 0 degrees C the uptake system is still active, with K(m) 132+/-26nm and V(max.) 1.8+/-0.3pmol of tri-iodothyronine/10min per 6x10(7) 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 Ca(2+) 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].
    [Abstract] [Full Text] [Related] [New Search]