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B M Mullock

Publications and source records attributed to B M Mullock.

At least 37 records · Page 2Linked to original sources
PubMed1987

The preparative isolation of endosome fractions: a review.

The endosome is an intracellular, acidic, membrane-bound, subcellular compartment to which endocytosed ligands, receptors and plasma membrane proteins are conveyed before sorting and delivery to destinations elsewhere in the cell. The preparative isolation of elements of this compartment has been achieved successfully using various appropriate combinations of density gradient ultracentrifugation, electrophoretic, gel filtration and immunoaffinity techniques. These methods for isolating endosome fractions are reviewed together with the difficulties of establishing markers for such fractions. The isolation of an endosome fraction from the pathway of polymeric IgA transcytosis in rat liver is discussed to exemplify successful isolation procedures and appropriate subcellular markers.

Animals↗
PubMed1985

Sources of proteins in human bile.

The proteins of 46 human bile specimens, collected by several different routes have been studied by crossed immunoelectrophoresis, by rocket immunoelectrophoresis and by radioimmunoassay. The results were analysed by plotting the variation in the bile: plasma ratio of particular proteins against molecular weight and by examination of the correlation between the concentrations of different proteins in the biles of different patients. Our results show that the majority of human bile proteins derive from plasma although bile specific proteins are always present. The majority of plasma proteins appear to enter bile by a 'sieving' mechanism which results in an inverse relationship between the bile: plasma ratio and the molecular weight. In addition there was a very high degree of correlation between the biliary concentrations of alpha 2-macroglobulin, IgG, haptoglobin, haemopexin, albumin, prealbumin, and orosomucoid. A number of other proteins namely thyroxine binding globulin, GC globulin and alpha 2HS-glycoprotein appeared in bile at concentrations greater than those expected if entry is by the sieving mechanism. These three proteins, however, are of rather low molecular weight and the reason for the lack of correlation appears to be individual variation in the 'pore size', presumably reflecting variation in the porosity of tight junction between hepatocytes. Although the majority of human bile proteins would appear to enter bile by a molecular weight-dependent pathway, four proteins, namely secretory IgA, IgM, haemoglobin and caeruloplasmin, showed significant deviation from the predicted relationship and probably enter bile at least partly by transport across cells. The concentration of beta 2-glycoprotein I was also much greater than expected from its molecular weight. The reason for this is not yet clear but may well reflect a very efficient and specific transport mechanism.

Bile↗
PubMed1983

Immune responses to chlorpromazine in rats. Detection and relation to hepatotoxicity.

It has frequently been suggested that the jaundice which occurs in a small percentage of human patients following treatment with chlorpromazine is due to a hypersensitivity reaction. It has, however, proved impossible to obtain an animal model for this condition. We now show that oral administration of chlorpromazine at 25 mg/kg per day to Wistar albino rats results in formation of both humoral and secretory antibodies to chlorpromazine. We also demonstrate that the severity of the hepatic changes observed in chlorpromazine-fed animals (periportal glycogen loss and centrilobular fatty change) is enhanced by preimmunization of the rats via the gut-associated lymphoid tissue with a chlorpramizine-protein conjugate. There was, however, no correlation between the titre of either serum or biliary antibodies in individual animals and the degree of liver damage. Our results therefore suggest than an immune mechanism is indeed implicated in chlorpromazine toxicity but show clearly that toxic symptoms are not a simple consequence of the formation of anti-chlorpromazine antibodies.

Animals↗
PubMed1983

Preparation of a low-density species of endocytic vesicle containing immunoglobulin A.

Immunoglobulin A is transported across hepatocytes in specialized vesicles. A population of endocytic vesicles of approx. 140 nm diameter, containing immunoglobulin A, has now been separated from all other major cytoplasmic organelles, including plasma membrane and lysosomes, by sequential centrifugation on Ficoll/sucrose and Metrizamide gradients.

Animals↗
PubMed1983

Proteins of guinea-pig bile: selective resorption in the gall bladder.

We have examined and compared the proteins present in guinea-pig bile as collected either from the common hepatic duct or from the gall bladder. Guinea-pig bile, collected from the common bile duct, has a rather low concentration of protein. Detailed examination shows that the concentrations of actively transported proteins such as immunoglobulin A and haptoglobin:haemoglobin complexes are markedly lower than in rats although the concentrations of proteins which, like albumin, leak non-specifically into bile are similar in the two species. We also find that the protein composition of guinea-pig bile is extensively and selectively modified by resorption of protein in the gall bladder.

Animals↗
PubMed1981

Enterohepatic circulation of IgA does not occur in rats.

The concentration of IgA in rat bile falls with time after cannulation. This effect is particularly marked in germ-free animals, in which the initial level of IgA is markedly subnormal anyway. The fall suggests that the cannula is draining to the exterior IgA, which would normally be recirculated. However, when germ-free or normal rats were supplied intraduodenally with bile whose IgA carried 125I, no transfer of this labelled IgA from the gut lumen back to the bile could be detected.

Animals↗
PubMed1980

Distribution of secretory component in hepatocytes and its mode of transfer into bile.

Immunoglobin A in bile and other external secretions is mostly bound to a glycoprotein known as secretory component. This glycoprotein is not synthesized by the same cells as immunoglobulin A and is not found in blood. We now report the mechanism by which secretory component reaches the bile and describe its function in immunoglobulin A transport across the hepatocyte. Fractionation of rat liver homogenates by zonal centrifugation was followed by measurement of the amounts of secretory component in the various fractions by rocket immunoelectrophoresis. Secretory component was found in two fractions. One of these was identified as containing Golgi vesicles from its isopycnic density and appearance in the electron microscope; the other contained principally fragments of the plasma membrane of the sinusoidal face of the hepatocyte, as shown by its particle size and content of marker enzymes. Only the latter fraction bound (125)I-labelled immunoglobulin A added in vitro. At 5min after intravenous injection of [(14)C]fucose, the secretory component in the Golgi fraction was labelled, but not that in the plasma membrane. The secretory component in the sinusoidal plasma membrane did, however, become labelled before the first labelled secretory component appeared in bile, about 30min after injection. We suggest that fucose is added to the newly synthesized secretory component in the Golgi apparatus. The secretory component then passes, with the other newly secreted glycoproteins, to the sinusoidal plasma membrane. There it remains bound but exposed to the blood and able to bind any polymeric immunoglobulin A present in serum. The secretory component then moves across the hepatocyte to the bile-canalicular face in association with the endocytic-shuttle vesicles which carry immunoglobulin A. Hence there is a lag before newly synthesized secretory component appears in bile.

Animals↗
PubMed1979

Secretory component as the receptor for polymeric IgA on rat hepatocytes.

Rat hepatocytes in short-term monolayer cultures bound radiolabeled polymeric rat IgA but not IgG. The binding of 125I-IgA was inhibited equally well by unlabeled polymeric IgA and by antiserum to rat secretory component (SC). The antibody to SC, after specific purification and radiolabeling, was bound to hepatocytes as effectively as the IgA. These results indicate that SC acts as the receptor for polymeric IgA on rat hepatocytes as it does on human gut epithelia, and that the transport of IgA from blood to bile in rats across the liver is analogous to that of IgA across human enterocytes.

Animals↗
PubMed1979

Endocytic vesicles in liver carry polymeric IgA from serum to bile.

The distributions both of endogenous IgA and of injected 125I-labelled IgA were determined amongst the components of a liver homogenate. Rate zonal sedimentation, under conditions where separation was principally determined by particle size, showed that IgA was tightly bound to material which sedimented in the size range of the larger endoplasmic reticulum fragments. Further fractionation of the components within this size range according to their densities, by isopycnic centrifugation, showed that the IgA was associated with small vesicles with a density range of 1.12--1.17 g/ml, quite distinct from endoplasmic reticulum fragments. We therefore conclude that the IgA is present in liver cells in a distinct class of vesicles, which are, presumably, responsible for the transport of IgA from blood to bile.

Animals↗
PubMed1979

Reflux of billiary components into blood in experimental intrahepatic cholestasis induced in rats by treatment with alpha-naphthylisothiocyanate.

The sera of rats treated with alpha-naphthylisothiocyanate, an agent reported to cause intrahepatic cholestasis, and of rats treated with carbon tetrachloride, are examined for evidence of leakage of bile into blood. The levels of the four bile components assayed, namely IgA, free IgA secretory component, the biliary isoenzyme of 5'-nucleotidase and of direct reacting (conjugated) bilirubin, were all elevated in the sera of rats treated with alpha-naphthylisothiocyanate. No change in any of these components was found in rats treated with carbon tetrachloride, indicating that their appearance in serum is not an inevitable consequence of damage to hepatocytes. As the bile components assayed reach bile by three different routes. their rapid appearance in the sera of rats treated with alpha-naphthylisothiocyanate indicates reflux of bile into blood, presumably as a result of mechanical obstruction of intraheptic bile ducts.

1-Naphthylisothiocyanate↗