Characterization of the Hepatocyte Plasma Membrane Transport Mechanism for Lactate

1981 ◽  
Vol 60 (3) ◽  
pp. 4P-5P ◽  
Author(s):  
J. P. Monson ◽  
J. A. Smith ◽  
R. D. Cohen ◽  
R. A. Iles
Keyword(s):  
Plasma Membrane ◽  
Membrane Transport ◽  
Transport Mechanism

scholarly journals Uptake of triiodothyronine and triiodothyroacetic acid in neonatal rat cardiomyocytes: effects of metabolites and analogs

2002 ◽  
Vol 173 (2) ◽  
pp. 247-255 ◽  
Author(s):  
FA Verhoeven ◽  
HH Van der Putten ◽  
G Hennemann ◽  
JM Lamers ◽  
TJ Visser ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Thyroid Hormone ◽  
Membrane Transport ◽  
Transport Mechanism ◽  
Horse Serum ◽  
Neonatal Rat ◽  
Rat Cardiomyocytes ◽  
Neonatal Rat Cardiomyocytes ◽  
Old Rats ◽  
Hormone Analogs

Cellular and nuclear uptake of [125I]tri-iodothyronine (T3) and [125I]triiodothyroacetic acid (Triac) were compared in cardiomyocytes of 2-3 day old rats, and the effect of thyroid hormone analogs on cellular T(3) uptake was measured. Cells (5-10 x 10(5) per well) were cultured in DMEM-M199 with 5% horse serum and 5% FCS. Incubations were performed for from 15 min to 24 h at 37 degrees C in the same medium, 0.5% BSA and [125I]T3 (100 pM), or [125I]Triac (240 pM). Expressed as % dose, T(3) uptake was five times Triac uptake, but expressed as fmol/pM free hormone, Triac uptake was at least 30% (P<0.001) greater than T3 uptake, whereas the relative nuclear binding of the two tracers was comparable. The 15 min uptake of [125I]T3 was competitively inhibited by 10 microM unlabeled T3 (45-52%; P<0.001) or 3,3'- diiodothyronine (T2) (52%; P<0.001), and to a smaller extent by thyroxine (T(4)) (27%; 0.05<0.1). In contrast, 10 microM 3,5-T2, Triac, or tetraiodothyroacetic acid (Tetrac) did not affect T3 uptake after 15 min or after 24 h. Diiodothyropropionic acid (DITPA) (10 microM) reduced 15-min T3 uptake by about 24% (P<0.05), but it had a greater effect after 4 h (56%; P<0.001). Exposure to 10 nM DITPA during culture reduced cellular T3 uptake, as did 10 nM T3, suggesting down-regulation of the plasma membrane T3 transporters. We conclude that i) Triac is taken up by cardiomyocytes; ii) 3,3'-T2 and, to a lesser extent, DITPA and T4 interfere with plasma membrane transport of T3, whereas 3,5-T2, Triac, or Tetrac do not; iii) the transport mechanism for Triac is probably different from that for T3.

scholarly journals Fluorescence Fluctuation Spectroscopy enables quantification of potassium channel subunit dynamics and stoichiometry

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Giulia Tedeschi ◽  
Lorenzo Scipioni ◽  
Maria Papanikolaou ◽  
Geoffrey W. Abbott ◽  
Michelle A. Digman
Keyword(s):  
Plasma Membrane ◽  
Protein Diffusion ◽  
Ion Diffusion ◽  
Fluorescence Fluctuation Spectroscopy ◽  
Biophysical Characterization ◽  
Kv Channels ◽  
Subunit Stoichiometry ◽  
Spatio Temporal ◽  
Voltage Sensing Domain

AbstractVoltage-gated potassium (Kv) channels are a family of membrane proteins that facilitate K+ ion diffusion across the plasma membrane, regulating both resting and action potentials. Kv channels comprise four pore-forming α subunits, each with a voltage sensing domain, and they are regulated by interaction with β subunits such as those belonging to the KCNE family. Here we conducted a comprehensive biophysical characterization of stoichiometry and protein diffusion across the plasma membrane of the epithelial KCNQ1-KCNE2 complex, combining total internal reflection fluorescence (TIRF) microscopy and a series of complementary Fluorescence Fluctuation Spectroscopy (FFS) techniques. Using this approach, we found that KCNQ1-KCNE2 has a predominant 4:4 stoichiometry, while non-bound KCNE2 subunits are mostly present as dimers in the plasma membrane. At the same time, we identified unique spatio-temporal diffusion modalities and nano-environment organization for each channel subunit. These findings improve our understanding of KCNQ1-KCNE2 channel function and suggest strategies for elucidating the subunit stoichiometry and forces directing localization and diffusion of ion channel complexes in general.

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