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I M Arias

Publications and source records attributed to I M Arias.

At least 91 records · Page 5Linked to original sources
PubMed1984

Glutathione transport across hepatocyte plasma membranes. Analysis using isolated rat-liver sinusoidal-membrane vesicles.

Transport of reduced glutathione (GSH) and its derivatives was studied in rat-liver sinusoidal plasma-membrane vesicles by a rapid filtration technique. The membrane vesicles exhibited transport of GSH into an osmotically active intravesicular space. Equilibrium uptake of vesicle-associated GSH was similar to that of free ligands which can be trapped by the intravesicular space of sinusoidal membrane samples. Kinetic analysis of the transport process revealed that the sinusoidal membrane vesicles have high-affinity and low-affinity GSH transport systems; the former has an apparent Km of 0.34 mM for GSH and V of 1.4 nmol X mg protein-1 X 20 s-1, and the latter has an apparent Km of 3.3 mM and V of 3.9 nmol X mg protein-1 X 20 s-1. Both Km values are lower than intrahepatic GSH levels, indicating that GSH transport across the sinusoidal membrane occurs via carrier-mediated mechanism and argues simple diffusion mechanism. The presence of oxidized glutathione (GSSG) or S-benzylglutathione inhibited GSH transport by the vesicles; the low-affinity transport system was inhibited more markedly than the high-affinity transport system. This suggests that these glutathione derivatives interacted preferentially with the low-affinity transport system for GSH. S-Dinitrophenylglutathione was also transported by the vesicles by a process which was inhibited by GSH and GSSG. The vesicles also transported GSSG, and this transport was markedly inhibited by S-benzylglutathione or GSH. The transport systems in sinusoidal plasma membranes may function in vivo in translocating GSH and its derivatives from hepatocytes into plasma and play an important role in inter-organ metabolism of these compounds.

Animals↗
PubMed1984

Taurocholate transport by rat liver canalicular membrane vesicles. Evidence for the presence of an Na+-independent transport system.

To elucidate the mechanism of vectorial translocation of bile acids in the liver, taurocholate transport was studied in isolated liver canalicular membrane vesicles by a rapid filtration method. The membrane vesicles revealed temperature-dependent, Na+-independent transport of taurocholate into an osmotically reactive intravesicular space. In the absence of sodium, taurocholate uptake followed saturation kinetics (apparent Km for taurocholate = 43 microM and Vmax = 0.22 nmol/mg protein X 20 s at 37 degrees C) and was inhibited by cholate and probenecid. Transstimulation by unlabeled taurocholate was also demonstrated. When the electrical potential difference across the membranes was altered by anion replacement, a more positive intravesicular potential stimulated, and a more negative potential inhibited, transport of taurocholate by the vesicles. Valinomycin-induced K+-diffusion potential (vesicle inside-positive) enhanced the rate of taurocholate uptake that was not altered by imposed pH gradients. These results indicate that rat liver canalicular plasma membrane contains a sodium-independent taurocholate transport system that translocates the bile acid as an anion across the membrane. In intact hepatocytes, the electrical potential difference across the canalicular membrane probably provides the driving force for taurocholate secretion. The contribution of nonionic diffusion to taurocholate secretion appears to be minimal.

Animals↗
PubMed1983

Differential regulation by triiodothyronine of substrate-specific uridinediphosphoglucuronate glucuronosyl transferases in rat liver.

Hepatic uridinediphosphoglucuronate glucuronosyl transferase (UDPglucuronyltransferase, EC 2.4.1.17) is functionally heterogeneous; 4-nitrophenol and bilirubin are representative substrates for two functional forms of the enzyme. UDPglucuronyltransferase activity for bilirubin and 4-nitrophenol was separated from solubilized rat liver microsomes by DEAE-cellulose chromatography and corresponding enzymes were purified. A radioimmunoassay was developed using a rabbit antiserum against purified rat 4-nitrophenol-specific UDPglucuronyltransferase, which precipitated enzyme activities toward both 4-nitrophenol and bilirubin. After treatment with triiodothyronine (T3) (0.55 mg/kg body weight), hepatic microsomal UDPglucuronyltransferase activity for 4-nitrophenol was increased 400% as compared to controls; the enzyme activity for bilirubin was decreased by 80%; the changes in the substrate-specific enzyme activities were reflected in the enzymatically active fractions separated after DEAE-cellulose chromatography. The changes in enzyme activities paralleled changes in the concentrations of the two corresponding UDP glucuronyltransferase proteins in the chromatographic fractions, as measured by radioimmunoassay. The results indicate that the opposite effects of T3 on the two forms of UDPglucuronyltransferase activity is due to its differential effect on corresponding enzyme proteins.

Animals↗
PubMed1983

The mechanism of biliary secretion of reduced glutathione. Analysis of transport process in isolated rat-liver canalicular membrane vesicles.

Transport of reduced glutathione (GSH) was studied in isolated rat liver canalicular membrane vesicles by a rapid filtration technique. The membrane vesicles exhibit uptake of [2-3H]glycine--labeled GSH into an osmotically reactive intravesicular space. Although the canalicular membrane vesicles possess gamma-glutamyltransferase and aminopeptidase M, enzymes that hydrolyze glutathione into component amino acids, inactivation of the vesicle-associated transferase by affinity labeling with L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125) had no effect on the initial rate of GSH transport. Chemical analysis revealed that intact GSH accounted for most of vesicle-associated radioactivity. The initial rate of transport followed saturation kinetics with respect to GSH concentration; an apparent Km of 0.33 mM and V of 1.47 nmol/mg protein in 20 s were calculated. These results indicate that transport of GSH across the canalicular membranes is a carrier-mediated process. Replacement of NaCl in the transport medium by KCl, LiCl or choline chloride had no effect on the transport activity of the vesicles. The rate of GSH uptake by the vesicles was enhanced by valinomycin-induced K+-diffusion potential (vesicle inside-positive) and was inhibited by probenecid, indicating that GSH transport across the canalicular membranes is electrogenic and involves the transfer of negative charge. The transport of GSH was inhibited by oxidized glutathione or S-benzyl-glutathione. This transport system in canalicular plasma membranes may function in biliary secretion of GSH and its derivatives which are synthesized in hepatocytes by oxidative processes or glutathione S-transferase.

Animals↗
PubMed1983

Rat liver canalicular membrane vesicles. Isolation and topological characterization.

Canalicular plasma membranes were isolated from rat liver homogenates using nitrogen cavitation and calcium precipitation methods. Compared with homogenates, the membranes were enriched 55- to 56-fold in gamma-glutamyltransferase, aminopeptidase M, and alkaline phosphatase activities and showed very low enrichment in markers of other membranes. By electron microscopy, the membrane preparation contained neither junctional complexes nor contaminating organelles and consisted exclusively of vesicles. The presence of vesicles was also evident from the osmotic sensitivity of D-[6-3H]glucose uptake into the membrane preparation. Antisera obtained from rabbits immunized with highly purified rat kidney gamma-glutamyltransferase inhibited the transferase activity of intact or Triton X-100-solubilized membranes by 45-55%. Treatment of vesicles with anti-gamma-glutamyltransferase antisera and anti-rabbit IgG antisera increased the apparent density of the membranes during sucrose density gradient centrifugation. gamma-Glutamyltransferase and aminopeptidase M activities were selectively removed from the vesicles by limited proteolysis with papain without changing the intravesicular space or alkaline phosphatase activity of the membranes. Specific binding of anti-gamma-glutamyltransferase antibody to the outer surface of isolated hepatocytes was observed as measured by the antisera and 125I-labeled protein A; binding followed saturation kinetics with respect to antibody concentration. These data indicate that the isolated canalicular membrane vesicles are exclusively oriented right-side-out and that gamma-glutamyltransferase and aminopeptidase M are located on the luminal side of rat liver canalicular plasma membranes.

Animals↗
PubMed1983

Hepatic ligandin subunits and mRNAs during development.

Eight-week-old rats had twofold higher hepatic ligandin concentration than 10-day-old animals as determined immunologically and by steroid isomerase and glutathione S-transferase assays. Increased ligandin content was accompanied by parallel increase in subunit synthesis as determined by [3H]leucine incorporation into each subunit relative to incorporation into total cytosolic proteins. The mRNA content for each ligandin subunit was twofold higher in older animals as determined by cell-free in vitro translation followed by immunoprecipitation and dot hybridization using a ligandin cDNA probe. When poly A mRNA from the postmitochondrial fraction of liver from young or old rats was subjected to agarose gel electrophoresis under denaturing conditions and hybridized to ligandin cDNA probe, a single 11 S band was obtained. With RNA from total liver, an additional 13 S band was obtained, suggesting the existence of a precursor form of ligandin mRNA. Since precursor polypeptides were not observed with RNA from total liver in cell-free in vitro translation systems, the precursor form requires processing to the 11 S form before the mRNA becomes functional.

Aging↗
PubMed1983

Regulation of growth and differentiation of a rat hepatoma cell line by the synergistic interactions of hormones and collagenous substrata.

Serum-free, hormonally defined media have been developed for optimal growth of a rat hepatoma cell line. The cells' hormonal requirements for growth are dramatically altered both qualitatively and quantitatively by whether they were plated onto tissue culture plastic or collagenous substrata. On collagenous substrata, the cells required insulin, glucagon, growth hormone, prolactin, and linoleic acid (bound to BSA), and zinc, copper, and selenium. For growth on tissue culture plastic, the cells required the above factors at higher concentrations plus several additional factors: transferrin, hydrocortisone, and triiodothyronine. To ascertain the relative influence of hormones versus substratum on the growth and differentiation of rat hepatoma cells, various parameters of growth and of liver-specific and housekeeping functions were compared in cells grown in serum-free, hormonally supplemented, or serum-supplemented medium and on either tissue culture plastic or type I collagen gels. The substratum was found to be the primary determinant of attachment and survival of the cells. Even in serum-free media, the cells showed attachment and survival efficiencies of 40-50% at low seeding densities and even higher efficiencies at high seeding densities when the cells were plated onto collagenous substrata. However, optimal attachment and survival efficiencies of the cells on collagenous substrata still required either serum or hormonal supplements. On tissue culture plastic, there was no survival of the cells at any seeding density without either serum or hormonal supplements added to the medium. A defined medium designed for cells plated on tissue culture plastic, containing increased levels of hormones plus additional factors over those in the defined medium designed for cells on collagenous substrata, was found to permit attachment and survival of the cells plated into serum-free medium and onto tissue culture plastic. Growth of the cells was influenced by both substrata and hormones. When plated onto collagen gel substrata as compared with tissue culture plastic, the cells required fewer hormones and growth factors in the serum-free, hormone-supplemented media to achieve optimal growth rates. Growth rates of the cells at low and high seeding densities were equivalent in the hormonally and serum-supplemented media as long as comparisons were made on the same substratum and the hormonally supplemented medium used was the one designed for that substratum. For a given medium, either serum or hormonally supplemented, the saturation densities were highest for tissue culture plastic as compared with collagen gels.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed1982

Hepatocellular ligandin during N-2-fluorenylacetamide carcinogenesis.

Ligandin was decreased by 75% as determined immunologically and by glutathione-S-transferase or steroid isomerase activities in rat hepatocellular carcinomas induced by exposure to N-2-fluorenylacetamide. Minor variable differences in ligandin levels were noted between the putative, premalignant nodules induced by this regimen and normal liver.

2-Acetylaminofluorene↗
PubMed1982

Bilirubin diglucuronide formation in intact rats and in isolated Gunn rat liver.

Bilirubin diglucuronide (BDG) may be formed in vitro by microsomal UDP glucuronosyl transferase (EC 2.4.1.17)-mediated transfer of a second mole of glucuronic acid from UDP-glucuronic acid, or by dismutation of bilirubin monoglucuronide (BMG) to BDG and unconjugated bilirubin, catalyzed by an enzyme (EC 2.4.1.95) that is concentrated in plasma membrane-enriched fractions of rat liver. To evaluate the role of these two enzymatic mechanisms in vivo, [(3)H]bilirubin mono-[(14)C]glucuronide was biosynthesized, purified by thin-layer chromatography, and tracer doses were infused intravenously in homozygous Gunn (UDP glucuronyl transferase-deficient) rats or Wistar rats. Bilirubin conjugates in bile were separated by high-pressure liquid chromatography and (3)H and (14)C were quantitated. In Gunn rats, the (14)C:(3)H ratio in BDG excreted in bile was twice the ratio in injected BMG. In Wistar rats the (14)C:(3)H ratio in biliary BDG was 1.25 +/- 0.06 (mean +/- SEM) times the ratio in injected BMG. When double labeled BMG was injected in Wistar rats after injection of excess unlabeled unconjugated bilirubin (1.7 mumol), the (14)C:(3)H ratio in BDG excreted in bile was identical to the ratio in injected BMG. Analysis of isomeric composition of bilirubin conjugates after alkaline hydrolysis or alkaline methanolysis indicated that the bile pigments retained the IX(alpha) configuration during these experiments. The results indicate that both enzymatic dismutation and UDP glucuronyl transferase function in vivo in BDG formation, and that dismutation is inhibited by a high intrahepatic concentration of unconjugated bilirubin. This hypothesis was supported by infusion of [(3)H]bilirubin-monoglucuronide in isolated perfused homozygous Gunn rat liver after depletion of intrahepatic bilirubin by perfusion with bovine serum albumin (2.5%), and after bilirubin repletion following perfusion with 0.34 mM bilirubin. From 20 to 25% of injected radioactivity was recovered in BDG in bile in the bilirubin-depleted state; only 8-10% of radioactivity was in BDG in bile after bilirubin repletion. After infusion of [(3)H]bilirubin di-[(14)C]glucuronide in homozygous Gunn rats, 5-7% of the injected pigment was excreted in bile as BMG. The (14)C:(3)H ratio in the injected BDG was 10% greater than the (14)C:(3)H ratio in BMG excreted in bile. These results indicate that in vivo, dismutation rather than partial hydrolysis, is responsible for BMG formation. Incubation of [(3)H]bilirubin, BDG and a rat liver plasma membrane preparation resulted in formation of BMG (3.3 nmol/min per mg protein) indicating that dismutation is also reversible in vitro.

Animals↗
PubMed1981

The effect of phenobarbital and 3'-methyl-N,N-dimethyl-4-aminoazobenzene administration on catalytic, binding and immunological properties of ligandin subunits in rat liver.

Following administration of phenobarbital to rats, liver ligandin content, bilirubin binding, glutathione-S-transferase and steroid isomerase activities increased by 150% and the 22000-dalton subunit was selectively increased. Following administration of 3'-methyl-N,N-dimethyl-4-aminoazobenzene, rat liver ligandin content and steroid isomerase decreased by 65%, glutathione-S-transferase increased by 100%, bilirubin binding was abolished, and the relative proportion of the 22000- and 25000-dalton subunits remained unchanged.

Animals↗
PubMed1981

Urinary ligandin and glutathione-S-transferase in gentamicin-induced nephrotoxicity in the rat.

1. Eight rats developed detectable glutathione-S-transferase activity in their urine after three daily injections of toxic doses of gentamicin. 2. Seven of the eight rats had immunodetectable ligandin in their urine at this time. 3. The level of enzyme activity correlated well with the degree of elevation of serum creatinine. 4. This confirms ligandinuria and urinary glutathione-S-transferase as markers of acute renal proximal tubular injury.

Animals↗