The action of flecainide acetate and its enantiomers on mammalian non-myelinated nerve fibres.

The effects of flecainide acetate racemate and its two enantiomers on voltage-operated sodium and potassium channels and on the sodium pump activity of non-myelinated fibres of the guinea-pig vagus nerve were studied with the sucrose-gap method. The racemic mixture as well as the R enantiomer and S enantiomer in a concentration range of 3 x 10(-5)-3 x 10(-4) M caused suppression of the compound action potential, a diminished propagation velocity and a reduction of the post-tetanic potential (PTH), which was also observed with lidocaine. There was no significant difference in the effect caused by the enantiomers separately.

Zonal compartmentation of perfused rat liver: plasma reappearance of rhodamine B explained.

Rhodamine B (RB) fluorescence reappears in perfusion medium of a cyclically perfused rat liver after a rapid initial removal phase. At the same time the compound redistributes in the liver from acinar zone 1 toward zone 3. By analysis of the metabolic profile of RB, and by inhibition of glucuronidation (the main metabolic route) with salicylamide, we show in this paper that formation and secretion of RB-conjugates from liver into perfusate is not involved in the reappearance and redistribution phenomena.

A study on the buffering activity of the human rectum. In vivo demonstration of HCO3- and H+ secretion after rectal application of fluids with an unphysiological pH.

The buffering activity of the human rectum was evaluated in various pilot studies, using a rectal lumen perfusion method. Quantitative alkaline and acid secretion was measured, respectively, by direct titration according to the pH-stat method. The change in composition of the perfusate with regard to the test drug benzoate and the concentration HCO3- was detected.

Covalent and noncovalent protein binding of drugs: implications for hepatic clearance, storage, and cell-specific drug delivery.

This review deals with the mechanisms by which the liver disposes of drugs that are covalently or noncovalently associated with proteins. Many drugs bind to plasma proteins such as albumin (mainly anionic compounds) and alpha 1-acid glycoprotein (cationic compounds). Nevertheless, the liver is able to clear such drugs efficiently from the circulation because of intrahepatic dissociation of the drug-protein complex.

Unequal disposition of enantiomers of the organic cation oxyphenonium in the rat isolated perfused liver.

This paper describes the results of pharmacokinetic experiments in the rat isolated perfused liver with enantiomers of oxyphenonium. The study was performed with the [14C]methyl labelled compounds. In this preparation both metabolism and biliary excretion were significantly different for the (+)- and the (-)-isomer.

Selective activity of several cholic acid derivatives against human immunodeficiency virus replication in vitro.

Several cholic acid derivatives such as taurolithocholic acid, lithocholic acid 3-sulfate, taurolithocholic acid 3-sulfate, and glycolithocholic acid 3-sulfate were shown to inhibit selectively the replication of human immunodeficiency virus type 1 (HIV-1) in vitro. These compounds completely protected MT-4 cells against HIV-1-induced cytopathogenicity at a concentration of 100 micrograms/ml, whereas no toxicity for the host cells was observed at 200 micrograms/ml. They also inhibited HIV-1 antigen expression in HIV-1-infected CEM cells.

Heterogeneous acinar localization of the asialoglycoprotein internalization system in rat hepatocytes.

Desialylated glycoprotein is rapidly cleared from plasma by a receptor-mediated endocytic mechanism located on hepatocytes. We studied the hepatic acinar distribution of this asialoglycoprotein transport system with the ligand 125I-asialoorosomucoid using rat liver perfused in either antegrade or retrograde direction in combination with quantitative light microscopic autoradiography. Grain distribution along the acinus appeared dependent on the perfusion direction.

Uptake and excretion of vecuronium bromide and pancuronium bromide in the isolated perfused rat liver.

Using the isolated perfused rat liver preparation, the disappearance from the perfusate and the excretion in the bile of vecuronium bromide and pancuronium bromide and their metabolites were followed for 2 h after the addition of 1 mg of either drug to the perfusate. In addition, the rate of change of the hepatic content of these two compounds was calculated by serially subtracting the amount of the compound and the metabolites in the bile and in the perfusate from the dose of drug added to the perfusate. It was found that, whereas the concentration of pancuronium in the perfusate declined slowly and monoexponentially, vercuronium concentration in the perfusate declined rapidly in a biexponential manner.

Evolution and mutagenesis of the mammalian excision repair gene ERCC-1.

The human DNA excision repair protein ERCC-1 exhibits homology to the yeast RAD10 repair protein and its longer C-terminus displays similarity to parts of the E. coli repair proteins uvrA and uvrC. To study the evolution of this 'mosaic' ERCC-1 gene we have isolated the mouse homologue.

Pharmacokinetics of biliary excretion in man. VI. Indocyanine green.

The pharmacokinetics of Indocyanine Green (ICG) has been studied in 15 patients given 0.5, 1.0 and 2.

Mechanisms for the hepatic uptake of organic cations. Studies with the muscle relaxant vecuronium in isolated rat hepatocytes.

In hepatobiliary transport of organic cations some remarkable differences have been reported between the monovalent compounds (prototype procainamidethobromide) and the potentially bivalent cations, containing a second quaternary ammonium group or a protonated tertiary amine function (prototype d-tubocurarine). In order to characterize the hepatic uptake mechanism for such bivalent cations in more detail, we studied the uptake of the steroidal muscle relaxant vecuronium in isolated rat hepatocytes. Uptake occurred by both a saturable (Vmax = 181 pmol/min x 10(6) cells, Km = 15 microM) and a nonsaturable process (rate constant = 1.

Molecular characterization of the testis specific c-abl mRNA in mouse.

The c-abl gene encodes a protein tyrosine kinase and is transcribed from at least two promoters giving rise to transcripts of two size classes of approximately 5 and 6 kb in length. These mRNAs only differ in their most 5' exon and encode proteins of similar size but with different N-termini. In the mouse testis an additional abundant c-abl mRNA of 4 kb is detected.

Hepatobiliary excretion of organic anions in double-mutant rats with a combination of defective canalicular transport and uridine 5'-diphosphate-glucuronyltransferase deficiency.

Mutant rats with a selective defect for the hepatobiliary excretion of organic anions (GT+TR- rats) are valuable models to study hepatic transport processes. However, retained conjugates in the livers of these rats may secondarily affect hepatic uptake, metabolism, and excretion of other compounds and this may confound the interpretation of test results. We have developed double mutants (GT-TR-) rats with both a conjugation and an excretion defect by cross-breeding uridine 5'-diphosphate-glucuronyl-transferase-deficient GT-TR+ Gunn rats with transport-deficient GT+TR- rats.

Unique fusion of bcr and c-abl genes in Philadelphia chromosome positive acute lymphoblastic leukemia.

The Philadelphia (Ph) chromosome, the product of t(9:22), is the cytogenetic hallmark of chronic myelogenous leukemia. The c-abl oncogene on chromosome 9 is translocated to the Ph chromosome and linked to a breakpoint cluster region (bcr), which is part of a large bcr gene. This results in the formation of a bcr-c-abl fusion gene, which is transcribed into an 8.

Acinar redistribution and heterogeneity in transport of the organic cation rhodamine B in rat liver.

We studied a possible acinar heterogeneity in the transport of organic cations, using rhodamine B as model compound. Employing perfusions of isolated rat livers in the ante- and retrograde mode and quantitative fluorescence microscopy, Zones 1 and 3 were shown to be equally efficient in taking up rhodamine B. Ten minutes after injection in an antegrade perfusion, 95% of the dose was localized in the portal half of the acinus.

Lactosylation of albumin reduces uptake rate of dibromosulfophthalein in perfused rat liver and dissociation rate from albumin in vitro.

Two types of models have recently been proposed to describe hepatic uptake kinetics of protein bound drugs: a model in which dissociation from plasma protein is rate limiting the process, and a model in which an interaction between protein and hepatocyte surface is thought to promote dissociation and uptake of the drug. This study was designed to investigate several aspects of both models, using lactosylated albumin as a binding protein that can interact with the Ashwell receptor abundantly present on the hepatocyte. Dibromosulfophthalein clearance was studied in rat liver in the presence of 150 microM (1%) albumin or 150 microM lactosylated albumin.

The structure of a human neurofilament gene (NF-L): a unique exon-intron organization in the intermediate filament gene family.

We have cloned and determined the nucleotide sequence of the human gene for the neurofilament subunit NF-L. The cloned DNA contains the entire transcriptional unit and generates two mRNAs of approx. 2.

The influence of binding to albumin and alpha 1-acid glycoprotein on the clearance of drugs by the liver.

The liver is a major site for synthesis and catabolism of plasma proteins. Albumin has various binding sites for anionic drugs, alpha 1-acid glycoprotein possesses a single binding site for cationic drugs. In spite of extensive protein binding, the liver can efficiently remove drugs from the circulation.

Hepatic disposition of cationic drugs bound to asialoorosomucoid: lack of coendocytosis and evidence for intrahepatic dissociation.

A combination of protein binding, liver clearance, subcellular distribution and cell separation experiments was employed to investigate the influence of binding of cationic drugs to asialoorosomucoid (ASOR) on their hepatic uptake and intrahepatic distribution. Two quaternary ammonium drugs, d-tubocurarine and N-methyldeptropine, were selected because of their marked differences in hepatic processing and binding to ASOR. In spite of an increase in protein binding of 560% for d-tubocurarine and 380% for N-methyldeptropine, perfusate clearance of both drugs in isolated perfused rat livers was not influenced by addition of 75 mg of ASOR.

Antigenicity and immunogenicity of synthetic peptides of foot-and-mouth disease virus.

Peptides reactive with two neutralizing monoclonal antibodies raised against intact foot-and-mouth disease virus A10 were identified with the aid of all overlapping (hexa)peptides of the outer structural viral protein VP1 and located on the viral surface. Using this procedure, it was possible to define those amino acids within a peptide which were critical in the binding of antibody to that peptide. One eight amino acid long peptide, containing six such amino acids, was virtually indistinguishable from viral antigen in its ability to bind monoclonal antibody as determined by competition tests.

Selective hepatobiliary transport defect for organic anions and neutral steroids in mutant rats with hereditary-conjugated hyperbilirubinemia.

Mutant rats (TM rats) with abnormal hepatic excretory function were used to study biliary transport of dibromosulfophthalein, ouabain, tributylmethyl ammonium, cholate and taurocholate. In whole animals, dibromosulfophthalein and ouabain clearance is reduced to 7 and 37% of normal, respectively, due to severely impaired excretion from liver to bile. Initial uptake rates of these agents are relatively little affected.

The human neurofilament gene (NEFL) is located on the short arm of chromosome 8.

We have localized the gene coding for the human neurofilament light chain (NEFL) to chromosome band 8p2.1 by Southern blotting of DNA from hybrid cell panels and in situ hybridization to metaphase chromosomes.

Pharmacokinetics of xamoterol glucuronidation in the rat in vivo and in liver perfusion.

Xamoterol has a phenolic hydroxyl group at which both sulphation and glucuronidation may occur. In the rat in vivo it is almost exclusively glucuronidated. In bile the glucuronide conjugate is the only metabolite of xamoterol.