Uptake of thyroid hormones in neonatal rat cardiac myocytes.

Abstract

The uptake and metabolism of T3 and T4 were investigated in cardiomyocytes isolated from 2-day-old rats. Myocytes (2-5 x 10(5) cells/well) were cultured for 1 day in medium with 5% horse serum-5% FCS and subsequently for 4 days without serum; in some cases myocytes were cultured with serum throughout the culture period. Experiments were performed at 37 C in medium with 0.5% BSA for measurement of [125I]T3 (200,000 cpm; 200 pM) uptake and with 0.1% BSA for measurement of [125I]T4 (200,000 cpm; 350 pM) uptake. Uptake of [125I]T3, expressed as femtomoles per picomolar concentration of free hormone, with any incubation time between 15 min and 24 h was at least 2-fold higher than that of [125I]T4. Neither T3 nor T4 was deiodinated within 24 h. This was observed in cells cultured in the absence or presence of serum. After 15 min of incubation, [125I]T3 uptake was 0.048 +/- 0.002 fmol/pM free T3 (n = 9), and [125I]T4 uptake was 0.018 +/- 0.003 fmol/pM free T4 (n = 9). Although [125I]T3 uptake was reduced by 31-40% (P < 0.05) by coincubation with 100 nM to 10 microM unlabeled T3, that of [125I]T4 was not affected by 1 nM to 10 microM unlabeled T4, nor was [125I]T3 uptake reduced by 10 microM unlabeled T4. Preincubation (30 min) and incubation (15 min) with 10 microM oligomycin reduced cellular ATP by 56% (P < 0.05) and [125I]T3 uptake by 73% (P < 0.05), but had no effect on [125I]T4 uptake. Similarly, [125I]T3 uptake, but not [125I]T4 uptake, was dependent on temperature and partly dependent on the Na+ gradient, as shown by the inhibitory effect of 10 microM monensin (27%; P < 0.05). The effect of aromatic amino acids (2 mM) on [125I]T3 uptake increased in the order phenylalanine < tyrosine < tryptophan. It is concluded that T3 is taken up in neonatal cardiomyocytes by an energy-dependent carrier-mediated mechanism that is also partly dependent on the Na+ gradient. Such a transport mechanism for T4 is not present in the neonatal heart, but it may appear later during development.

The history of a developmental stage: Metamorphosis in chordates

“…(10) Finally, within the cell, upon thyroactive compound binding, TR will modulate the expression of target genes. The direct synthesis of T 3 in the thyroid gland, along with the peripheral deiodination of T 4 , is an important source of active hormone since cellular uptake is faster for T 3 than for T 4 (Everts et al, 1996).…”

A physiological role for glucuronidated thyroid hormones: Preferential uptake by H9c2(2-1) myotubes

“…It has been shown earlier that the uptake of radiolabeled T4 and T3 in primary cultures of rat cardiomyocytes (Everts et al, 1996) and in H9c2(2-1) myoblasts and myotubes is not completely inhibited by the addition of a surplus of unlabeled hormone, suggesting that the transport of T4 and T3 is not mediated by a single transport protein. We here show that native, unconjugated T4 partly inhibits the uptake of T4G in H9c2(2-1) cells, probably by competition for the same transporter site.…”

“…Primary cultures of neonatal rat cardiac fibroblasts were prepared as described previously (Everts et al, 1996). Hearts were digested using trypsin to obtain a cell suspension.…”

Negative association between free triiodothyronine level and international normalized ratio in euthyroid subjects with acute myocardial infarction

“…Recently, Lymvaios et al reported that T3 levels are closely correlated with the cardiac function after AMI [22] . Everts et al also reported that T3, and not T4, is transported into the myocyte [23] . However, the exact mechanisms underlying the association between FT3 and cardiac function require further study.…”