Short-term effects of thyroid hormones and 3,5-diiodothyronine on membrane transport systems in chick embryo hepatocytes.
Rapid nongenomic effects of thyroid hormones L-T(3) and L-T(4) on two plasma membrane transport systems were investigated in 14-d-old and 19-d-old chick embryo hepatocytes. The Na(+)/H(+) exchanger activity was measured using the intracellular pH-sensitive fluorescent probe 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester, whereas the amino acid transport was estimated by [1-(14)C]-2-aminoisobutyric acid uptake. System A amino acid transport activation was linear to hormone concentration, whereas the Na/H exchanger gave a bell-shaped dose-response curve, with a maximum at the physiological hormone concentration of 1 nM. The specificity of the effect was verified by the use of inhibitors and analogues. The thyroid hormone analog 3,5-diiodo-L-thyronine was able to mimic some of the hormone effects, but with a lower efficiency. The effect on the Na(+)/H(+) exchanger was identified for 14-d-old and 19-d-old cells, whereas the amino acid transport could only be activated at the late stage of embryo development. Both transport systems were activated through a signal transduction pathway involving PKC, MAPK pathway, and PI3K, even though the differences in response behavior indicate a differential modulation of the two transport systems by L-T(3) and L-T(4). These results clearly demonstrate the existence of rapid nongenomic action of thyroid hormones also in avian cells, and show that activation of System A amino acid transport is not directly correlated to changes in intracellular pH. For the first time, evidence is presented which suggests that short-term effects of thyroid hormones may play a role during fetal development and cell differentiation.
Incerpi
Sandra
S
Department of Biology, University of Rome Roma Tre, Viale Marconi 446, 00146 Rome, Italy. incerpi@uniroma3.it
De Vito
Paolo
P
Luly
Paolo
P
Spagnuolo
Silvana
S
Leoni
Silvia
S
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002642:Chick Embryo; D004104:Diiodothyronines / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism; D013963:Thyroid Hormones / Q000494:pharmacology*
D000596:Amino Acids; D004104:Diiodothyronines; D004791:Enzyme Inhibitors; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D017923:Sodium-Hydrogen Exchangers; D013963:Thyroid Hormones; C030103:3,5-diiodothyronine