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  1. Article: Carbon monoxide and sepsis: is a toxic gas good for your liver?

    Weisiger, R A

    Gastroenterology

    2001  Volume 120, Issue 5, Page(s) 1288–1291

    MeSH term(s) Carbon Monoxide/metabolism ; Humans ; Liver/metabolism ; Sepsis/metabolism
    Chemical Substances Carbon Monoxide (7U1EE4V452)
    Language English
    Publishing date 2001-04
    Publishing country United States
    Document type Comment ; Editorial ; Review
    ZDB-ID 80112-4
    ISSN 1528-0012 ; 0016-5085
    ISSN (online) 1528-0012
    ISSN 0016-5085
    DOI 10.1053/gast.2001.23592
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  2. Article: Saturable stimulation of fatty acid transport through model cytoplasm by soluble binding protein.

    Weisiger, R A

    The American journal of physiology

    1999  Volume 277, Issue 1, Page(s) G109–19

    Abstract: To better define the role of soluble binding proteins in the cytoplasmic transport of amphipathic molecules, we measured the diffusional mobility of a fluorescent long-chain fatty acid, 12-N-methyl-(7-nitrobenz-2-oxa-1,3-diazol)aminostearate (NBD- ... ...

    Abstract To better define the role of soluble binding proteins in the cytoplasmic transport of amphipathic molecules, we measured the diffusional mobility of a fluorescent long-chain fatty acid, 12-N-methyl-(7-nitrobenz-2-oxa-1,3-diazol)aminostearate (NBD-stearate), through model cytoplasm as a function of soluble binding protein concentration. Diffusional mobilities were correlated with the partition of the fatty acid between membrane and protein binding sites. Cytoplasm was modeled as a dense suspension of liposomes, and albumin was used as a model binding protein. Albumin saturably increased NBD-stearate mobility through the membrane suspension approximately eightfold. Fatty acid mobility in the absence of albumin was identical to the mobility of the membrane vesicles (1.99 +/- 0.33 x 10(-8) cm(2)/s), whereas the mobility at saturating concentrations was identical to the mobility of albumin (1.65 +/- 0.12 x 10(-7) cm(2)/s). The protein concentration producing half-maximal stimulation of NBD-stearate diffusion (42.8 +/- 0.3 microM) was unexpectedly greater than that required to solubilize half of the NBD-stearate (17.9 +/- 3.0 microM). These results support a proposed mechanism for cytoplasmic transport of small amphipathic molecules in which aqueous diffusion of the protein-bound form of the molecule largely determines the transport rate. However, slow interchange of fatty acid between the binding protein and membranes also appears to influence the transport rate in this model system.
    MeSH term(s) 4-Chloro-7-nitrobenzofurazan/analogs & derivatives ; 4-Chloro-7-nitrobenzofurazan/metabolism ; Albumins/metabolism ; Albumins/pharmacology ; Biological Transport/drug effects ; Biological Transport/physiology ; Carrier Proteins/chemistry ; Carrier Proteins/metabolism ; Centrifugation ; Chemical Fractionation ; Cytoplasm/metabolism ; Diffusion ; Fatty Acids/metabolism ; Liposomes/metabolism ; Liposomes/ultrastructure ; Models, Biological ; Osmolar Concentration ; Serum Albumin, Bovine/metabolism ; Serum Albumin, Bovine/pharmacology ; Stearates/metabolism
    Chemical Substances Albumins ; Carrier Proteins ; Fatty Acids ; Liposomes ; Stearates ; 12-N-methyl-7-nitrobenzo-2-oxa-1,3-diazolamino stearate (117056-67-4) ; Serum Albumin, Bovine (27432CM55Q) ; 4-Chloro-7-nitrobenzofurazan (EQF2794IRE)
    Language English
    Publishing date 1999
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 2948-8
    ISSN 0002-9513
    ISSN 0002-9513
    DOI 10.1152/ajpgi.1999.277.1.G109
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  3. Article: Modulation of aspartate aminotransferase release and fatty acid uptake by ethanol.

    Weisiger, R A

    Hepatology (Baltimore, Md.)

    1998  Volume 27, Issue 4, Page(s) 1162–1163

    MeSH term(s) Aspartate Aminotransferases/secretion ; Ethanol/toxicity ; Fatty Acids/metabolism ; Humans ; Liver/drug effects ; Liver/enzymology
    Chemical Substances Fatty Acids ; Ethanol (3K9958V90M) ; Aspartate Aminotransferases (EC 2.6.1.1)
    Language English
    Publishing date 1998-04
    Publishing country United States
    Document type Editorial ; Comment
    ZDB-ID 604603-4
    ISSN 1527-3350 ; 0270-9139
    ISSN (online) 1527-3350
    ISSN 0270-9139
    DOI 10.1002/hep.510270435
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  4. Article: When is a carrier not a membrane carrier? The cytoplasmic transport of amphipathic molecules.

    Weisiger, R A

    Hepatology (Baltimore, Md.)

    1996  Volume 24, Issue 5, Page(s) 1288–1295

    Abstract: After entering the cell, small molecules must penetrate the cytoplasm before they are metabolized, excreted, or can convey information to the cell nucleus. Without efficient cytoplasmic transport, most such molecules would efflux back out of the cell ... ...

    Abstract After entering the cell, small molecules must penetrate the cytoplasm before they are metabolized, excreted, or can convey information to the cell nucleus. Without efficient cytoplasmic transport, most such molecules would efflux back out of the cell before they could reach their targets. Cytoplasmic movement of amphipathic molecules (e.g., long-chain fatty acids, bilirubin, bile acids) is greatly slowed by their tendency to bind intracellular structures. Soluble cytoplasmic binding proteins reduce this binding by increasing the aqueous solubility of their ligands. These soluble carriers catalyze the transport of hydrophobic molecules across hydrophilic water layers, just as membrane carriers catalyze the transport of hydrophilic molecules across the hydrophobic membrane core. They even display the kinetic features of carrier-mediated transport, including saturation, mutual competition between similar molecules, and countertransport. Recent data suggest that amphipathic molecules cross the cytoplasm very slowly, with apparent diffusion constants 10(2) to 10(4) times smaller than in water. By modulating the rate of cytoplasmic transport, cytosolic binding proteins may regulate transport and metabolism of amphipathic molecules. Storage diseases may cause hepatocellular dysfunction by disrupting normal cytoplasmic transport.
    MeSH term(s) Animals ; Biological Transport/drug effects ; Carrier Proteins/metabolism ; Cytoplasm/metabolism ; Cytoskeleton/physiology ; Diffusion ; Humans ; Permeability
    Chemical Substances Carrier Proteins
    Language English
    Publishing date 1996-11
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S. ; Review
    ZDB-ID 604603-4
    ISSN 1527-3350 ; 0270-9139
    ISSN (online) 1527-3350
    ISSN 0270-9139
    DOI 10.1002/hep.510240550
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  5. Article: Transfer of fatty acids between intracellular membranes: roles of soluble binding proteins, distance, and time.

    Weisiger, R A / Zucker, S D

    American journal of physiology. Gastrointestinal and liver physiology

    2002  Volume 282, Issue 1, Page(s) G105–15

    Abstract: Soluble fatty acid binding proteins (FABPs) are thought to facilitate exchange of fatty acids between intracellular membranes. Although many FABP variants have been described, they fall into two general classes. "Membrane-active" FABPs exchange fatty ... ...

    Abstract Soluble fatty acid binding proteins (FABPs) are thought to facilitate exchange of fatty acids between intracellular membranes. Although many FABP variants have been described, they fall into two general classes. "Membrane-active" FABPs exchange fatty acids with membranes during transient collisions with the membrane surface, whereas "membrane-inactive" FABPs do not. We used modeling of fatty acid transport between two planar membranes to examine the hypothesis that these two classes catalyze different steps in intracellular fatty acid transport. In the absence of FABP, the steady-state flux of fatty acid from the donor to the acceptor membrane depends on membrane separation distance (d) approaching a maximum value (J(max)) as d approaches zero. J(max) is one-half the rate of dissociation of fatty acid from the donor membrane, indicating that newly dissociated fatty acid has a 50% chance of successfully reaching the acceptor membrane before rebinding to the donor membrane. For larger membrane separations, successful transfer becomes less likely as diffusional concentration gradients develop. The mean diffusional excursion of the fatty acid into the water phase (d(m)) defines this transition. For d<<d(m), dissociation from the membrane is rate limiting, whereas for d>>d(m), aqueous diffusion is rate limiting. All forms of FABP increase d(m) by reducing the rate of rebinding to the donor membrane, thus maintaining J(max) over larger membrane separations. Membrane-active FABPs further increase J(max) by catalyzing the rate of dissociation of fatty acids from the donor membrane, although frequent membrane interactions would be expected to reduce their diffusional mobility through a membrane-rich cytoplasm. Individual FABPs may have evolved to match the membrane separations and densities found in specific cell lines.
    MeSH term(s) Animals ; Biological Transport/physiology ; Carrier Proteins/metabolism ; Diffusion ; Fatty Acid-Binding Proteins ; Fatty Acids/pharmacokinetics ; Intracellular Membranes/metabolism ; Kinetics ; Models, Biological ; Neoplasm Proteins ; Reproducibility of Results ; Solubility ; Time Factors
    Chemical Substances Carrier Proteins ; Fatty Acid-Binding Proteins ; Fatty Acids ; Neoplasm Proteins
    Language English
    Publishing date 2002-01
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 603840-2
    ISSN 1522-1547 ; 0193-1857
    ISSN (online) 1522-1547
    ISSN 0193-1857
    DOI 10.1152/ajpgi.00238.2001
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  6. Article: Models of hepatic elimination.

    Weisiger, R A

    Hepatology (Baltimore, Md.)

    1986  Volume 6, Issue 2, Page(s) 338–340

    MeSH term(s) Animals ; Liver/metabolism ; Models, Biological ; Pharmaceutical Preparations/metabolism ; Propranolol/metabolism ; Rats ; Receptors, Albumin ; Receptors, Cell Surface/metabolism
    Chemical Substances Pharmaceutical Preparations ; Receptors, Albumin ; Receptors, Cell Surface ; Propranolol (9Y8NXQ24VQ)
    Language English
    Publishing date 1986-03
    Publishing country United States
    Document type Letter ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 604603-4
    ISSN 1527-3350 ; 0270-9139
    ISSN (online) 1527-3350
    ISSN 0270-9139
    DOI 10.1002/hep.1840060239
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  7. Article: Oxygen radicals and ischemic tissue injury.

    Weisiger, R A

    Gastroenterology

    1986  Volume 90, Issue 2, Page(s) 494–496

    MeSH term(s) Animals ; Cats ; Digestive System/blood supply ; Digestive System/metabolism ; Free Radicals ; Ischemia/etiology ; Oxygen/toxicity ; Superoxide Dismutase/metabolism ; Xanthine Dehydrogenase/metabolism
    Chemical Substances Free Radicals ; Superoxide Dismutase (EC 1.15.1.1) ; Xanthine Dehydrogenase (EC 1.17.1.4) ; Oxygen (S88TT14065)
    Language English
    Publishing date 1986-02
    Publishing country United States
    Document type Journal Article
    ZDB-ID 80112-4
    ISSN 1528-0012 ; 0016-5085
    ISSN (online) 1528-0012
    ISSN 0016-5085
    DOI 10.1016/0016-5085(86)90955-8
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  8. Article: Dissociation from albumin: a potentially rate-limiting step in the clearance of substances by the liver.

    Weisiger, R A

    Proceedings of the National Academy of Sciences of the United States of America

    1985  Volume 82, Issue 5, Page(s) 1563–1567

    Abstract: The hepatic uptake rate for certain albumin-bound drugs and metabolites correlates poorly with their equilibrium unbound concentration in the plasma, suggesting that binding equilibrium may not always exist within the hepatic sinusoids. Currently ... ...

    Abstract The hepatic uptake rate for certain albumin-bound drugs and metabolites correlates poorly with their equilibrium unbound concentration in the plasma, suggesting that binding equilibrium may not always exist within the hepatic sinusoids. Currently available models for the uptake process assume binding equilibrium and, thus, cannot be used to investigate this possibility. This report presents a more general model that treats plasma-bound and free concentrations separately. A solution is provided that specifies the hepatic uptake rate as a function of the total plasma concentrations of the transported substance and of binding protein and the rate constants for influx, efflux, elimination, association, dissociation, and flow. Analysis of this solution indicates that hepatic uptake may be limited by the rate of plasma flow, dissociation from the binding protein, influx into the liver, cellular elimination, or any combination of these processes. The affinity and concentration of the binding protein strongly influence which of these steps are rate-limiting in any given case, and binding equilibrium exists within the hepatic sinusoids only for binding protein concentrations greater than a specified value (the ratio of the uptake and association rate constants). The precise conditions under which each step is rate-limiting and the kinetic behavior expected when two or more steps mutually limit uptake are provided. The results are compatible with previously reported data for the uptake of certain albumin-bound ligands such as bilirubin, and they offer an alternative to attributing these kinetics to the presence of an albumin receptor.
    MeSH term(s) Biological Transport ; Kinetics ; Ligands ; Liver/metabolism ; Protein Binding ; Serum Albumin/metabolism
    Chemical Substances Ligands ; Serum Albumin
    Language English
    Publishing date 1985-03
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 209104-5
    ISSN 1091-6490 ; 0027-8424
    ISSN (online) 1091-6490
    ISSN 0027-8424
    DOI 10.1073/pnas.82.5.1563
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  9. Article: Nontraditional effects of protein binding and hematocrit on uptake of indocyanine green by perfused rat liver.

    Ott, P / Weisiger, R A

    The American journal of physiology

    1997  Volume 273, Issue 1 Pt 1, Page(s) G227–38

    Abstract: We used a novel parameter-free approach to study the role of protein binding in the hepatic clearance of indocyanine green (ICG) from reconstituted pig blood by perfused rat liver. Either perfusate total plasma protein concentration or hematocrit was ... ...

    Abstract We used a novel parameter-free approach to study the role of protein binding in the hepatic clearance of indocyanine green (ICG) from reconstituted pig blood by perfused rat liver. Either perfusate total plasma protein concentration or hematocrit was changed. By analyzing protein concentration ratios or plasma volume ratios relative to ratios of intrinsic hepatic clearance of ICG (K), it was possible to evaluate current models of hepatic uptake of protein-bound ligands without precise knowledge of some of the model parameters. A four-fold increase in the total plasma protein concentration produced only a 36% decrease in K. This was substantially less than predicted by the traditional model, where K is proportional to the free concentration of ligand. Because an unstirred water layer effect could not by itself account for the observations, the effects of binding disequilibrium in the sinusoids or uptake directly from the bound pool had to be considered. To discriminate, hematocrit was increased from 15% to 29%, causing a 20% decrease in the sinusoidal plasma volume. A significant reduction in K strongly suggested a sinusoidal binding disequilibrium effect. The dissociation rate constant predicted by this model was confirmed by in vitro measurement, further supporting this interpretation. The simple experimental design and its parameter-free evaluation provide a new tool for investigating the hepatic uptake of protein-bound ligands.
    MeSH term(s) Animals ; Biological Transport ; Blood Proteins/metabolism ; Erythrocytes/metabolism ; Female ; Hematocrit ; Indocyanine Green/pharmacokinetics ; Kinetics ; Liver/metabolism ; Metabolic Clearance Rate ; Models, Biological ; Perfusion ; Protein Binding ; Rats ; Rats, Wistar ; Regression Analysis ; Swine
    Chemical Substances Blood Proteins ; Indocyanine Green (IX6J1063HV)
    Language English
    Publishing date 1997-07
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 2948-8
    ISSN 0002-9513
    ISSN 0002-9513
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  10. Article: Toxic waste or hormone? Carbon monoxide as a regulator of sinusoidal tone.

    Weisiger, R A / Rockey, D C

    Hepatology (Baltimore, Md.)

    1996  Volume 24, Issue 5, Page(s) 1319–1321

    MeSH term(s) Adipocytes/physiology ; Animals ; Carbon Monoxide/metabolism ; Heme Oxygenase (Decyclizing)/metabolism ; Liver/cytology ; Liver/metabolism ; Liver Circulation ; Nitric Oxide/physiology ; Rats
    Chemical Substances Nitric Oxide (31C4KY9ESH) ; Carbon Monoxide (7U1EE4V452) ; Heme Oxygenase (Decyclizing) (EC 1.14.14.18)
    Language English
    Publishing date 1996-11
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 604603-4
    ISSN 1527-3350 ; 0270-9139
    ISSN (online) 1527-3350
    ISSN 0270-9139
    DOI 10.1002/hep.510240555
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