Short-Term Effects of Thyroid Hormones and 3,5-Diiodothyronine on Membrane Transport Systems in Chick Embryo Hepatocytes

Abstract

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.

3,3′,5-Triiodo-l-thyronine Up-regulation of Na,K-ATPase Activity and Cell Surface Expression in Alveolar Epithelial Cells Is Src Kinase- and Phosphoinositide 3-Kinase-dependent

“…Recently, Incerpi et al (11) reported that T3 stimulated Na ϩ /H ϩ exchanger in chick embryo hepatocytes. This effect was sensitive to PI3K inhibitor wortmannin (50 nM), but direct activation of PI3K by T3 was not demonstrated.…”

“…Thyroid hormone (T4) recently was reported to activate the mitogen-activated protein kinase in HeLa and CV-1 cells (10). The T3-induced activity of Na ϩ /H ϩ exchanger and system A amino acid transport in chick embryo hepatocytes was blocked by inhibitors of protein kinase C and PI3K (11). Thyroid hormone differentially regulates Na,K-ATPase isoforms in both tissue-and cell type-specific manners (1).…”

Thyroid: biological actions of ‘nonclassical’ thyroid hormones

“…Intracellular action of T 2 also is described in avian cells during fetal development and cell differentiation (Incerpi et al 2002). T 2 regulates DNA synthesis, cell-cycle proteins (Alisi et al 2004), and several membrane-associated transport systems, whose activity is related to cell proliferation (Incerpi et al 2002(Incerpi et al , 2005.…”

“…T 2 regulates DNA synthesis, cell-cycle proteins (Alisi et al 2004), and several membrane-associated transport systems, whose activity is related to cell proliferation (Incerpi et al 2002(Incerpi et al , 2005. T 2 's effect on the Na C -H C exchanger was identified for 14-day-and 19-dayold cells, whereas the effect on amino acid transport was present at late stages of embryo development.…”

“…T 2 's effect on the Na C -H C exchanger was identified for 14-day-and 19-dayold cells, whereas the effect on amino acid transport was present at late stages of embryo development. Both transport systems were activated through a signal transduction pathway involving the PKC, MAPK, and PI3K pathways (Incerpi et al 2002). Moreover, T 2 exerts a short-term inhibitory effect on the Na C -K C -ATPase, the magnitude of which strongly correlates to the developmental age of the isolated cells (Scapin et al 2009).…”