Ultrastructural studies of the dying-back process. V. Axonal neurofilaments accumulate at sites of 2,5-hexanedione application: Evidence for nerve fibre dysfunction in experimental hexacarbon neuropathy

Brain Cell Biology - This study examines the thesis that 2,5-hexanedione (2,5-HD) produces distal (dying-back) axonopathy by direct toxic action on nerve fibres. Single or repeated application of...     

The free and the β2-microglobulin-associated heavy chains of HLA-A,B alloantigens share the antigenic determinant recognized by the monoclonal antibody Q1/28

Serological and immunochemical assays have shown that the monoclonal antibody Q1/28 recognizes an antigenic determinant which is expressed on the heavy chain of subsets of HLA-A, B antigens and is distinct from those defining the serological polymorphism of this system. Association of the HLA-A, B heavy chain with ₂-microglobulin is not required for expression of the antigenic determinant recognized by the monoclonal antibody Q1/28, since this antibody can immunoprecipitate a 45 000 m. w. component from radiolabeled lymphoid-cell glycoproteins immunodepleted with either an anti-human ₂-microglobulin xenoantiserum or the MoAb W6/32 to framework determinants of HLA-A, B, C antigens. Furthermore, the MoAb Q1/28 can immunoprecipitate a 45 000 m. w. component from an NP40lysate of radiolabeled Daudi cells, which lack the genetic information for ₂-microglobulin. The determinant recognized by the MoAb Q1/28 is relatively resistant to denaturing treatments and does not appear to be carbohydrate in nature. The MoAb Q1/28 is the first example of an antibody which recognizes an antigenic determinant expressed on both the ₂-microglobulin-associated and free HLA-A, B heavy chains.     

Presynaptic tubular structures in photoreceptor cells

Summary After the application of fixatives including phosphotungstic acid or a mixture of osmium tetroxide and zinc iodide, complex tubular structures are evident in the presynaptic side of the synapses between photoreceptor and bipolar cells of the rat's retina. In the first case only the limiting membranes are visualized, while in the second only the content of the tubules is stained. These tubules seem to be related, on a morphological ground, with the formation of synaptic vesicles. These tubular structures are not observed when fixation is done with osmium tetroxide or glutaraldehyde-osmium tetroxide.This work has been supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina, and from National Institutes of Health, U.S.A., (5 RO1 NS 06953-05 NEUA).We want to express our gratitude to Mrs. Haydée Agoff de Zimman and Mr. Alberto Saénz for their skillful technical assistance.     

Taurolithocholate-induced inhibition of biliary lipid and protein excretion in the rat.

Taurolithocholate (TLC), a natural bile salt, induces selective impairment on canalicular membrane of the hepatocyte, which seems to be a major determinant of its cholestatic effect in experimental animals. In order to extend existing studies about the effects of TLC on bile secretion, we examined in TLC-treated rats the biliary excretion of compounds that are transported to canalicular membrane via vesicles, such as lipids and proteins. The single intravenous injection of TLC (3 mumol/100 g body wt.) inhibited transiently the biliary bile salt excretion, while the biliary excretion of lipids (i.e., cholesterol and phospholipids) and proteins remained inhibited even though the biliary excretion and composition of bile salts were normalized. Under such a condition, TLC also inhibited the transcellular vesicular pathway to the exogenous protein horseradish peroxidase entry into bile, without altering the paracellular biliary access of the protein. The hepatic uptake of horseradish peroxidase was unaffected by TLC-treatment. The results indicate that TLC can inhibit the biliary excretion of compounds that reach the canaliculus via a vesicular pathway, such as lipids and proteins, by a mechanism not related to a defective bile salt excretion. Possible explanations for these findings are discussed.     

Comparison of hepatic, renal and intestinal bilirubin UDP-glucuronyl transferase activities in rat microsomes

1. Bilirubin UDP-glucuronyltransferase activity and its dependence on substrate concentrations in rat liver, renal cortex and intestinal mucosa microsomes were studied. 2. Bilirubin monoglucuronide synthesis from unconjugated bilirubin was a higher capacity, lower affinity step in comparison with bilirubin diglucuronide formation in the three tissues tested. 3. Bilirubin glucuronide formation in liver microsomes showed a higher capacity but a lower affinity than extrahepatic ones. Renal cortex and intestinal mucosa exhibited similar kinetics parameters. 4. In vitro bilirubin glucuronidation in renal cortex and intestinal mucosa was quantitatively important as compared with the hepatic one.