Inhibitory effects of calcium channel blockers on thyroid hormone uptake in neonatal rat cardiomyocytes

Lipophilic but not hydrophilic statin functionally inhibit volume-activated chloride channels by inhibiting NADPH oxidase in monocytes

Volume-activated Cl^- channels (VACCs) can be activated by hypotonic solutions and have been identified in many cell types. Here, we investigated the effects of different statins on VACCs in monocytes. Whole-cell patch clamp recordings demonstrated that a hypotonic solution induced 5-nitro-2- (3-phenylpropylamino) benzoic acid (NPPB)- and 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS)-sensitive VACC currents in human peripheral monocytes and RAW 264.7 cells. The VACC currents were inhibited by the lipophilic statin (simvastatin) but not by the hydrophilic simvastatin acid and pravastatin. A low-molecular-weight superoxide anion scavenger (tiron, 1 mM) and inhibitor of NADPH oxidase (DPI 10 μM) was able to abolish the VACC currents. A hypotonic solution increased the reactive oxygen species (ROS) detected by the fluorescence of dichlorodihydrofluorescein (DCF), which was abolished by tiron and DPI. NPPB, DIDS, and simvastatin but not pravastatin decreased the fluorescence of DCF. Simvastatin could not further decrease VACC currents when pretreated with tiron or DPI, whereas exogenous H₂O₂ (100 μM), increased the VACC currents and overcame the blockade of VACC currents by simvastatin. Functionally, hypotonic solution increased the TNF-α mRNA expression, which could be decreased by tiron, DPI, NPPB, DIDS and simvastatin but not pravastatin. However, simvastatin could not decrease the TNF-α expression further when pretreatment with tiron, DPI, NPPB or DIDS. We conclude that lipophilic (simvastatin) rather than hydrophilic statin inhibit VACCs and decrease hyposmolality induced inflammation in monocytes by inhibiting NADPH oxidase.

Transport of thyroxine and 3,3',5-triiodothyronine in human umbilical vein endothelial cells

The prerequisite for the uptake of thyroid hormone (TH) in peripheral tissues is the exit of TH from the bloodstream. The first step in this process is transport across the endothelium. Little is known about this important step in TH physiology. Therefore, we aimed to characterize the TH transport processes across the endothelium using human umbilical vein endothelial cells as a model. Transport studies showed rapid uptake of 1 nm [(125)I]T(3) and [(125)I]T(4) in these cells. The apparent Michaelis constant value for [(125)I]T(3) uptake was about 1 microm, and the IC(50) for T(4) inhibition of T(3) uptake was about 3 microm. The aromatic amino acids phenylalanine, tyrosine, and tryptophan and the L-type amino acid transporter-specific ligand 2-aminobicyclo-(2, 2, 1)-heptane-2-carboxylic acid did not inhibit [(125)I]T(3) or [(125)I]T(4) uptake. Verapamil was capable of reversibly reducing transport of [(125)I]T(3) and [(125)I]T(4). Human umbilical vein endothelial cells incubated with the affinity label BrAcT(3) resulted in a labeling of multiple proteins, which are probably protein disulfide isomerase related. Extrapolating our findings to the endothelial lining of blood vessels suggests that T(3) and T(4) uptake is mediated by the same transport system. Because TH transport characteristics do not correspond to known TH transporters, further studies are required to identify the TH transporter protein(s) at the molecular level. Possible candidates may be widely expressed Na(+)-independent transporter proteins.

A phosphorimager-based filter binding thyroid hormone receptor competition assay for chemical screening

INTRODUCTION

A phosphorimager-based filter binding thyroid hormone receptor (THR) competition assay has been developed for use in verifying hits from compound library screens.

METHODS

This method employs in vitro translated ligand binding domains (LBDs) of THRalpha and THRbeta, separation through nitrocellulose via a 96-well vacuum manifold, and analysis of receptor-bound radioactivity by phosphorimaging.

RESULTS

A standard curve of [I(125)]T3 showed a linear response over the dynamic range of a competition assay, and a comparison of Sephadex G-25 column separation and gamma counting with en masse filtration and phosphorimaging revealed similar IC(50) and K(i) values when using unlabeled T3 as competitor. In addition, this method produced IC(50) and K(i) values for the known T3 competitors [3,5-Dimethyl-4-(4'-hydoxy-3'-isopropylbenzyl) phenoxy] acetic acid (GC-1) and 3,5-diiodothyropropionic acid (DITPA) similar to those reported elsewhere.

DISCUSSION

These data suggest that filtration and phosphorimaging adequately and properly reproduces binding values associated with THR competition. Further, this method gave a 3-fold reduction in time and a 40-fold reduction in radioactive waste over the column-based method. These reductions allow for a substantial increase in assay throughput. Taken together, these data suggest that en masse filtration and phosphorimaging is an efficient and tractable method for verifying large groups of putative T3 competitors in vitro.