title: Uptake of tri-iodothyronine and thyroxine in myoblasts and myotubes of the embryonic heart cell line H9c2(2-1).
abstract: Uptake of tri-iodothyronine (T(3)) was compared with that of thyroxine (T(4)) in the embryonic heart cell line H9c2 (2-1). These cells propagate as myoblasts and form differentiated myotubes upon reduction of the serum concentration, as indicated by a 31-fold increase in creatine kinase activity. Protein and DNA content per well were around 2-fold higher in myotubes than in myoblasts. When expressed per well, T(3) and T(4) uptake were, compared with myoblasts, 1.9- to 2-fold and 3.1- to 4-fold higher in myotubes respectively. On the other hand, the characteristics of T(3) and T(4) uptake were similar in myoblasts and myotubes. At any time-point, T(4) uptake was 2-fold higher than that of T(3), and both uptakes were energy but not Na(+) dependent. T(3) and T(4) uptake exhibited mutual inhibition in myoblasts and myotubes: 10 microM unlabeled T(3) reduced T(4) uptake by 51-60% (P<0.001), while 10 microM T(4) inhibited T(3) uptake by 48-51% (P<0.001). Furthermore, T(3) and T(4) uptake in myoblasts was dose-dependently inhibited by tryptophan (maximum inhibition around 70%; P<0.001). Exposure of the cells to T(3) or T(4) during differentiation significantly increased the fusion index (35 and 40%; P < 0.01). Finally, both myoblasts and myotubes showed a small deiodinase type I activity, while deiodinase type II activity was undetectable. In conclusion, T(3) and T(4) share a common energy-dependent transport system in H9c2(2-1) cells, that may be important for the availability of thyroid hormone during differentiation.
authors.affiliation: Department of Veterinary Anatomy and Physiology, Utrecht University, PO Box 80.157, 3508 TD Utrecht, The Netherlands.
authors.forename: H H A G M
authors.initials: HH
authors.lastname: van der Putten
authors.forename: B J L J
authors.initials: BJ
authors.lastname: Joosten
authors.forename: P H M
authors.initials: PH
authors.lastname: Klaren
authors.forename: M E
authors.initials: ME
authors.lastname: Everts
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002460:Cell Line; D004627:Embryonic Induction / Q000502:physiology; D006321:Heart / Q000196:embryology*; D007453:Iodide Peroxidase / Q000378:metabolism; D008858:Microscopy, Phase-Contrast; D032386:Myoblasts, Cardiac / Q000378:metabolism*; D051381:Rats; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D014284:Triiodothyronine; D007453:Iodide Peroxidase; D013974:Thyroxine