RESUMO
The polymeric immunoglobulin receptor on rat hepatocytes binds dimeric IgA on the sinusoidal surface and mediates its transport to the canaliculus, where the complex of dimeric IgA and secretory component, the cleaved extracellular domain of polymeric immunoglobulin receptor, is secreted into bile. This process is unique in that disulfide bonds are formed between dimeric IgA and polymeric immunoglobulin receptor during transcytosis, permanently preventing their dissociation. Here we present three lines of evidence that disulfide bonding between dimeric IgA and polymeric immunoglobulin receptor occurs predominantly in a late transcytotic compartment and that hepatic transcytosis can proceed in the absence of disulfide bond formation. First, throughout the course of transcytosis the percentage of intracellular dimeric IgA disulfide bonded to polymeric immunoglobulin receptor is less than half that in bile, suggesting that disulfide bond formation is a late event in transcytosis. Second, dimeric IgA that recycles from early endocytotic compartments into the circulation is mostly noncovalently bound to secretory component. Finally, the rate of transcytosis of dimeric IgA and its appearance in bile are not affected when disulfide bond formation with polymeric immunoglobulin receptor is inhibited by blocking of free thiol groups on dimeric IgA with iodoacetamide. These results are consistent with other findings in the literature and indicate that the main physiological role of disulfide bond formation between dimeric IgA and polymeric immunoglobulin receptor is not to facilitate transcytosis but, rather, to stabilize the dimeric IgA-secretory component complex after its release into external secretions such as bile and intestinal secretions.
Assuntos
Dissulfetos/metabolismo , Endocitose , Exocitose , Imunoglobulina A/metabolismo , Fígado/metabolismo , Receptores Imunológicos/metabolismo , Animais , Bile/metabolismo , Compartimento Celular , Fígado/citologia , Fígado/imunologia , Masculino , Polímeros , Ratos , Ratos Sprague-Dawley , Componente Secretório/metabolismoRESUMO
To identify a role for amino acids in cholestasis associated with total parenteral nutrition, we measured bile formation by the isolated perfused rat liver in the presence and absence of added amino acids. All livers were infused constantly with sodium [14C]taurocholate (0.28 mumoles per min) for 90 min. At 40 min, a primed-constant infusion of a synthetic L-amino acid mixture (121 + 19.3 mumoles of N per min) was administered for an additional 50 min. Mean bile flow rates during the amino acid infusion were reduced from 15.4 microliter per min per 10 gm liver weight to 10.4 microliter per min per 10 gm (p less than 0.005). There was no significant change during saline infusion of control livers, and there was no significant difference in perfusate osmolalities in the two groups. Although biliary recovery of infused taurocholate was slightly lower in the experimental perfusions than in controls (95.3% vs. 101.7%, p less than 0.05), there was no significant reduction in taurocholate excretion rate during the infusion in either group. Bile flow changes were related to ambient concentrations and net fluxes of individual amino acids in the perfusate. Of the 14 infused amino acids, glycine and arginine achieved levels greater than 3 times greater than reported physiological postprandial portal venous concentrations in the rat, and together constituted about 25% of the 90-min perfusate amino acids (8.3 mM). The highest net hepatic uptake was for glycine (125 mumoles per hr per 10 gm), which was almost 50% of its infusion rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Assuntos
Aminoácidos/administração & dosagem , Colestase/etiologia , Fígado/metabolismo , Nutrição Parenteral Total/efeitos adversos , Nutrição Parenteral/efeitos adversos , Aminoácidos/metabolismo , Animais , Colestase/metabolismo , Masculino , Concentração Osmolar , Perfusão , Ratos , Ratos EndogâmicosAssuntos
Proteínas Sanguíneas/análise , Cromatografia DEAE-Celulose , Hemopexina/análise , Precursores de Proteínas/análise , Albumina Sérica/análise , Transferrina/análise , Absorção , Autoanálise , Eletroforese das Proteínas Sanguíneas , Cromatografia por Troca Iônica , Humanos , Imunoeletroforese , Métodos , Espectrofotometria UltravioletaAssuntos
Albuminas/biossíntese , Técnicas Citológicas , Fígado/citologia , Albuminas/análise , Aminoácidos , Animais , Separação Celular , Sobrevivência Celular , Células Cultivadas , Meios de Cultura , Estudos de Avaliação como Assunto , Imunodifusão , Lisina/metabolismo , Masculino , Consumo de Oxigênio , Ratos , Fatores de Tempo , Trítio , Azul Tripano/metabolismoRESUMO
1. The isolated perfused rat liver was used to study degradation rates of plasma albumin, transferrin and fibrinogen. 2. Constant fractional rates were observed for all three proteins even when the albumin concentration was drastically increased by the addition of large amounts to the perfusate pool. 3. Livers taken from rats deprived of dietary protein for 14-18 days showed greatly diminished fractional catabolic rates for albumin when perfused with blood from similarly deprived animals. 4. These rates could be restored to near-normal values by adding albumin or by perfusing with blood from normally fed rats. 5. These findings are consistent with the theory of pinocytosis as a step in the degradation of plasma proteins by hepatic parenchymal cells.
Assuntos
Proteínas Sanguíneas/metabolismo , Fígado/metabolismo , Deficiência de Proteína/metabolismo , Albumina Sérica/metabolismo , Animais , Fibrinogênio/metabolismo , Técnicas In Vitro , Isótopos de Iodo , Perfusão , Pinocitose , Ratos , Transferrina/metabolismoRESUMO
1. A method is described for the isolation of certain of the alpha(1)-globulins of rat plasma that are known to increase in concentration after tissue damage (acute-phase globulins). 2. Although apparently homogeneous when examined by disc electrophoresis at pH9, these proteins could be subdivided further by isoelectric fractionation. 3. Treatment with neuraminidase removed approx. 60% of the sialic acid originally present in these proteins and gave almost completely homogeneous material of decreased mobility when examined by disc electrophoresis in polyacrylamide gel. When subjected to immunoelectrophoresis this material gave a single arc. 4. The homogeneity of the isolated materials was examined by ultracentrifugation. The single peak thus found is consistent with molecular weights of 45000-46000. 5. The isolated materials were shown to be glycoproteins containing approx. 15% of carbohydrate, and to have isoelectric points in the range pH4.4-4.8.