Biomedical subjects

Z S Li

Publications and source records attributed to Z S Li.

At least 37 records · Page 2Linked to original sources

PubMed1997

AtMRP1 gene of Arabidopsis encodes a glutathione S-conjugate pump: isolation and functional definition of a plant ATP-binding cassette transporter gene.

Because plants produce cytotoxic compounds to which they, themselves, are susceptible and are exposed to exogenous toxins (microbial products, allelochemicals, and agrochemicals), cell survival is contingent on mechanisms for detoxifying these agents. One detoxification mechanism is the glutathione S-transferase-catalyzed glutathionation of the toxin, or an activated derivative, and transport of the conjugate out of the cytosol. We show here that a transporter responsible for the removal of glutathione S-conjugates from the cytosol, a specific Mg2+-ATPase, is encoded by the AtMRP1 gene of Arabidopsis thaliana. The sequence of AtMRP1 and the transport capabilities of membranes prepared from yeast cells transformed with plasmid-borne AtMRP1 demonstrate that this gene encodes an ATP-binding cassette transporter competent in the transport of glutathione S-conjugates of xenobiotics and endogenous substances, including herbicides and anthocyanins.

ATP-Binding Cassette Transporters↗

PubMed1997

Albumin transfer across the choroid plexus of South American opossum (Monodelphis domestica).

1. Blood-cerebrospinal fluid (CSF) transfer of various exogenous albumins has been investigated in developing Monodelphis domestica (South American grey short-tailed opossum) and compared with the steady-state CSF: plasma ratios for endogenous (Monodelphis) albumin. Ratios for Monodelphis albumin and human albumin were similar and were the highest at postnatal day 5 (P5) (48.2 +/- 4.4 and 40.6 +/- 4.5%, respectively). The ratio for bovine albumin was similar to the steady-state ratio for Monodelphis albumin at P7-8 but became consistently lower than the Monodelphis albumin ratio at all other ages until P32-36 when all albumins tested attained a similar low ratio. The CSF:plasma ratio of chemically modified (succinylated) bovine albumin was always significantly lower than that of other albumins, except at the oldest age examined (P32-36). 2. Immunocytochemistry showed that within the brain, albumin was confined to the lumen and endothelial cells of blood vessels. In the choroid plexus only a small proportion (0.2-1.7% of the total cell number) of epithelial cells was positive for albumin, both endogenous and exogenous, at all ages studied (except the 3rd ventricle where cells were only positive from P8). The CSF was strongly positive for all albumins. The peak proportion of positive cells and of albumin concentrations in CSF occurred at P8. These findings suggest that the primary route for penetration of albumin into CSF is directly across the choroid plexus rather than via the brain. 3. Double-labelling immunocytochemistry revealed that the same epithelial cells contained both endogenous (Monodelphis) and exogenous (human) albumin. In contrast, for succinylated albumin, at P7 only about 35% (lateral ventricle) and 50% (4th ventricle) of Monodelphis albumin-positive cells were also positive for succinylated albumin, but by P30 this proportion increased to 90% at both sites. 4. Thus the developing choroid plexus distinguishes between different albumins. Chemical modification of albumin (succinylation) disrupts this mechanism. It is proposed that in older animals (P32-36) all of the albumin in the CSF is derived from plasma by diffusion (as in adult animals). At earlier stages of development, a proportion of the albumin in CSF also appears to be transferred from the plasma by diffusion with an additional component transferred by a mechanism that can distinguish between different species of albumin. The main route of entry of albumin to CSF seems likely to be via the choroid plexus epithelial cells.

Albumins↗

PubMed1997

A new pathway for vacuolar cadmium sequestration in Saccharomyces cerevisiae: YCF1-catalyzed transport of bis(glutathionato)cadmium.

The yeast cadmium factor (YCF1) gene encodes an MgATP-energized glutathione S-conjugate transporter responsible for the vacuolar sequestration of organic compounds after their S-conjugation with glutathione. However, while YCF1 was originally isolated according to its ability to confer resistance to cadmium salts, neither its mode of interaction with Cd2+ nor the relationship between this process and organic glutathione-conjugate transport are known. Here we show through direct comparisons between vacuolar membrane vesicles purified from Saccharomyces cerevisiae strain DTY167, harboring a deletion of the YCF1 gene, and the isogenic wild-type strain DTY165 that YCF1 mediates the MgATP-energized vacuolar accumulation of Cd-glutathione complexes. The substrate requirements, kinetics and Cd2+/glutathione stoichiometry of cadmium uptake and the molecular weight of the transport-active complex demonstrate that YCF1 selectively catalyzes the transport of bis(glutathionato)cadmium (Cd x +GS2). On the basis of these results--the Cd2+ hypersensitivity of DTY167, versus DTY165, cells, the inducibility of YCF1-mediated transport, and the rapidity and spontaneity of Cd-GS2 formation--this new pathway is concluded to contribute substantially to Cd2+ detoxification.

ATP-Binding Cassette Transporters↗

PubMed1997

Transthyretin distribution in the developing choroid plexus of the South American opossum (Monodelphis domestica).

The distributions of transthyretin and albumin in the choroid plexus during brain development have been compared. The South American opossum was chosen because the young are born around the time of choroid plexus formation. Previous work showed that in the adult opossum, transthyretin is expressed in the choroid plexus cells. However, systematic studies of transthyretin in the choroid plexus during development have not been carried out before. Transthyretin was present in 90-95% of the choroidal cells form birth to adulthood. In most cells, transthyretin immunoreactivity was concentrated in the apical region of the cytoplasm. Double labelling of choroid plexus sections with antibodies to albumin and transthyretin showed that 1-2% of cells were positive for both proteins. These findings suggest that from the very earliest stage of choroid plexus formation most epithelial cells both synthesize and contain transthyretin, and a few of these transthyretin-synthesizing cells also contain albumin that is probably being transferred form blood to the cerebrospinal fluid.

Age Factors↗

PubMed1997

Vacuolar uptake of the phytoalexin medicarpin by the glutathione conjugate pump.

We have studied the uptake of [3H]-medicarpin and its glutathione conjugate(s) into vacuolar membrane vesicles from etiolated hypocotyls of mung bean (Vigna radiata). Unconjugated medicarpin is taken up at a low rate in the presence or absence of MgATP. However, [3H]-medicarpin-glutathione conjugate(s), prepared by incubation of medicarpin with a total maize glutathione S-transferase preparation, is taken up more than four-fold faster than medicarpin in the presence of MgATP, and this uptake is MgATP-dependent. Uptake of medicarpin-glutathione was not significantly inhibited by the ionophore gramicidin-D, but was strongly inhibited by vanadate and the alternative transport substrate S-(2,4-dinitrophenyl) glutathione. Our results demonstrate, in a model system, the potential utilization of the high affinity, high capacity, uncoupler-insensitive glutathione conjugate pump for the vacuolar transport of an isoflavonoid phytoalexin.

Adenosine Triphosphate↗

PubMed1997

The GS-X pump in plant, yeast, and animal cells: structure, function, and gene expression.

This review addresses the recent molecular identification of several members of the glutathione S-conjugate (GS-X) pump family, a new class of ATP-binding cassette (ABC) transporters responsible for the elimination and/or sequestration of pharmacologically and agronomically important compounds in mammalian, yeast and plant cells. The molecular structure and function of GS-X pumps encoded by MRP, cMOAT, YCF1, and AtMRP genes, have been conserved throughout molecular evolution. The physiologic function of GS-X pumps is closely related with cellular detoxification, oxidative stress, inflammation, and cancer drug resistance. Coordinated expression of GS-X pump genes, e.g., MRP1 and YCF1, and gamma-glutamylcystaine synthetase, a rate-limiting enzyme of cellular glutathione (GSH) biosynthesis, has been frequently observed.

Animals↗

PubMed1996

The yeast cadmium factor protein (YCF1) is a vacuolar glutathione S-conjugate pump.

The yeast cadmium factor gene (YCF1) from Saccharomyces cerevisiae, which was isolated according to its ability to confer cadmium resistance, encodes a 1,515 amino acid ATP-binding cassette (ABC) protein with extensive sequence homology to the human multidrug resistance-associated protein (MRP1) (Szczypka, M., Wemmie, J. A., Moye-Rowley, W. S., and Thiele, D. J. (1994) J. Biol. Chem. 269, 22853-22857). Direct comparisons between S. cerevisiae strain DTY167, harboring a deletion of the YCF1 gene, and the isogenic wild type strain, DTY165, demonstrate that YCF1 is required for increased resistance to the toxic effects of the exogenous glutathione S-conjugate precursor, 1-chloro-2,4-di-nitrobenzene, as well as cadmium. Whereas membrane vesicles isolated from DTY165 cells contain two major pathways for transport of the model compound S-(2,4-dinitrophenyl)glutathione (DNP-GS), an MgATP-dependent, uncoupler-insensitive pathway and an electrically driven pathway, the corresponding membrane fraction from DTY167 cells is more than 90% impaired for MgATP-dependent, uncoupler-insensitive DNP-GS transport. Of the two DNP-GS transport pathways identified, only the MgATP-dependent, uncoupler-insensive pathway is subject to inhibition by glutathione disulfide, vanadate, verapamil, and vinblastine. The capacity for MgATP-dependent, uncoupler-insensitive conjugate transport in vitro strictly copurifies with the acuolar membrane fraction. Intact DTY165 cells, but not DTY167 cells, mediate vacuolar accumulation of the quorescent glutathione-conjugate, monochlorobimane-GS. Introduction of plasmid borne, epitope-tagged gene encoding functional YCF1 into DTY167 cells alleviates the 1-chloro-2,4-dinitrobenzene-hypersensitive phenotype concomitant with restoration of the capacity of vacuolar membrane vesicles isolated from these cells for MgATP-dependent, uncoupler-insensitive DNP-GS transport. On the basis of these findings, the YCF1 gene of S. cerevisiae is inferred to encode an MgATP-energized, uncoupler-insensitive vacuolar glutathione S-conjugate transporter. The energy requirements, kinetics, substrate specificity, and inhibitor profile of YCF1-mediated transport demonstrate that the vacuolar glutathione conjugate pump of yeast bears a strong mechanistic resemblance to the MRP1-encoded transporter of mammalian cells and the cognate, but as yet molecularly undefined, function of plant cells.

ATP-Binding Cassette Transporters↗

PubMed1995

Do vasoactive intestinal peptide (VIP)- and nitric oxide synthase-immunoreactive terminals synapse exclusively with VIP cell bodies in the submucous plexus of the guinea-pig ileum?

In the submucous plexus of the guinea-pig ileum, previous light-microscopic studies have revealed that vasoactive intestinal peptide (VIP)-immunoreactive and nitric oxide synthase (NOS)-immunoreactive terminals are found predominantly in association with VIP-immunoreactive nerve cell bodies. In this study, double-label immunohistochemistry at the light-microscopic level demonstrated co-localization of NOS-immunoreactivity and VIP-immunoreactivity in axon terminals in submucous ganglia. About 90% of nerve fibres with NOS-immunoreactivity or VIP-immunoreactivity were immunoreactive for both antigens; only about 10% of labelled varicosities contained only NOS-immunoreactivity or VIP-immunoreactivity. The VIP/NOS varicosities were more often seen in the central parts of the ganglia, close to the VIP-immunoreactive cell bodies. Ultrastructural immunocytochemistry with antibodies to VIP was used to determine if NOS/VIP terminals synapse exclusively with VIP-immunoreactive nerve cell bodies. We examined the targets of VIP-immunoreactive boutons in two submucous ganglia from different animals. Serial ultrathin sections were taken through the ganglia after they had been processed for VIP immunocytochemistry. For each cell body, the number of VIP inputs (synapses and close contacts) was determined. The number of VIP-immunoreactive synapses received by the cell bodies of submucous neurons varied from 0-4 and the number of VIP-immunoreactive close contacts varied from 3-10. There was no significant difference between VIP-immunoreactive nerve cell bodies and non-VIP nerve cell bodies in the number of VIP-immunoreactive synapses and close contacts they received. Thus, the implication from light microscopy that NOS/VIP terminals end predominantly on VIP nerve cells was not vindicated by electron microscopy.

Animals↗

PubMed1994

Affinity purification of sucrose binding proteins from the plant plasma membrane.

Purified plasma membranes from sugar beet leaves were solubilized by 1% 3-((3-cholamidopropyl)dimethylammonio)-1-propanesulfonate and loaded on a sepharose 6 B column substituted with sucrose. Elution with sucrose at pH 5.2 yielded a peak that represented 0.2% of the loaded protein. This peak did not appear when the samples were pretreated with either 0.5 mM N-ethylmaleimide (NEM) or 0.5 mM para-chloromercuribenzenesulfonic acid. It was also absent when palatinose, a sucrose analogue not recognized by the sucrose transporter, was used as the affinity ligand. The peak specifically eluted by sucrose from the sucrose-Sepharose column exhibited sucrose transport activity after reconstitution into proteoliposomes. This peak was further fractionated by ion-exchange chromatography on a Mono-Q column, and the different fractions obtained were differentially labeled by [3H]NEM in the presence of sugars recognized (sucrose, maltose) or not recognized (palatinose) by the sucrose transporter. The data allowed to identify two fractions that were enriched with two polypeptides (56 and 41 kDa) differentially labeled by NEM in the presence of sucrose.

Biological Transport↗

PubMed1994

Nitric oxide synthase in the enteric nervous system of the guinea-pig: a quantitative description.

The distribution and abundance of nitric oxide synthase (NOS)-containing neurons and their terminals in the gastrointestinal tract of the guinea-pig were examined in detail using NADPH diaphorase histochemistry and NOS immunohistochemistry. NOS-containing cell bodies were found in the myenteric plexus throughout the gastrointestinal tract and in the submucous plexus of the stomach, colon and rectum. NOS-containing neurons comprised between 12% (in the duodenum) and 54% (in the esophagus) of total myenteric neurons. In the ileum, NOS neurons represented 19% of total myenteric neurons. Most of the NOS neurons throughout the gastrointestinal tract possessed lamellar dendrites and a single axon. NOS-containing terminals were abundant in the circular muscle, including that of the sphincters, but were rare in the longitudinal muscle, except for the taeniae of the caecum. The muscularis mucosae of the esophagus, stomach, colon and rectum received a medium to dense innervation by NOS terminals. Within myenteric ganglia, NOS-containing terminals were extremely sparse in the esophagus, stomach and duodenum, common in the ileum and distal colon and extremely dense in the proximal colon and rectum. The submucous plexus in the ileum and large intestine contained a sparse plexus of NOS-containing terminals. NOS terminals were not observed in the mucosa of any region. We conclude that throughout the gastrointestinal tract of the guinea-pig, NOS neurons are inhibitory motor neurons to the circular muscle; in the ileum and large intestine, NOS neurons may also function as interneurons.

Amino Acid Oxidoreductases↗

PubMed1994

Nitric oxide synthase in neurons of the gastrointestinal tract of an avian species, Coturnix coturnix.

The distribution of reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining and its colocalisation with nitric oxide synthase immunoreactivity was examined in neurons of the quail gastrointestinal tract. Immunoreactivity and enzyme activity were found in identical populations of neurons. Nitric oxide synthase activity was present in 30-40% of myenteric nerve cells in each region. Numerous reactive cells were also in the submucous plexus and many positive nerve fibres innervated the muscle. In the small intestine, some of the fibres innervating the circular muscle formed a deep muscular plexus and in the large intestine there was a submuscular plexus. Nerve fibres formed baskets around nerve cells of myenteric and submucous ganglia. Intramural arterioles were innervated, most prominently in the oesophagus and stomach. Very few fibres innervated the mucosa, except for some oesophageal glands and the core of villi in the cloaca. It is concluded that nitric oxide is probably involved in transmission to muscle of the avian intestine, as it is in mammals, and that it is probably also produced at neuroneuronal and neurovascular junctions.

Amino Acid Oxidoreductases↗

PubMed1994

[Distribution of rabies antigen in human tongue and salivary gland].

The distribution of rabies virus antigen (RVAg) in human tongue and salivary glands from three cases was studied with ABC immunohistochemical method. Of the 5 tissue blocks from 2 tongues, large amounts of RVAg were found in 4 tissue blocks, located in the serous glands, terminal nerves, some striated muscle fibers and some covering epithelium including taste cells of circumvallate papillae. Only small amounts of RVAg were present in 4 of the 9 salivary gland blocks, either within the acini or in nerves. These results differ from that reported previously in dog, fox and skunk salivary glands, which contained abundant RVAg. The amount of RVAg in human tongue is apparently greater than that in the salivary glands. It is probable that the serous glands of the human tongue are sites of predilection for RVAg and may serve as a source of infection.

Adolescent↗

PubMed1993

Nitric oxide synthase in the enteric nervous system of the rainbow trout, Salmo gairdneri.

The distribution of nitric oxide synthase (NOS) was determined in the gastrointestinal tract of the rainbow trout, Salmo gairdneri. NOS immunoreactivity and the NADPH diaphorase histochemical reaction were co-localized in nerve cells in the myenteric ganglia. However, only about 60% of NADPH diaphorase-stained nerve cells in the vagus nerve trunks were immunoreactive for NOS. Reactive myenteric nerve cells were found throughout the gastrointestinal tract, comprising about 10-15% of all nerve cells. Reactive nerve cells and fibres appeared in the myenteric ganglia and nerve trunks. The circular muscle was innervated by reactive nerve fibres throughout the gastrointestinal tract. Some NOS-containing cell bodies were also in this layer. The submucous plexus contained reactive nerve fibres in each region of the gut; in the large intestine a few reactive nerve cell bodies were also seen in this plexus. The muscle in the mucosal folds of the large intestine was densely innervated. The observations suggest that nitric oxide is an enteric transmitter in teleost fish, as it is in mammals.

Amino Acid Oxidoreductases↗

PubMed1993

[Pharmacokinetics of moracizine and moracizine sulfoxide in healthy volunteers].

The pharmacokinetics of moracizine (Mor) and moracizine sulfoxide (Mor-SO) determined by reversed phase HPLC was reported. The data in 6 volunteers after a single oral dose (600 mg) showed an one-compartment open model. The peak concentration in plasma (2.1 +/- 0.4 micrograms.ml-1) of Mor reached within 1-2 h. The Mor-SO concentration in plasma was much lower (0.19 +/- 0.06 micrograms.ml-1) than that of Mor, but its elimination T1/2 (2.3 +/- 1.0 h) was similar to that of Mor (1.5 +/- 1.0 h). The recoveries of Mor, Mor-SO, moracizine sulfone (Mor-SO2) in urine within 48 h were 0.07%, 0.25%, and 0.06% of the total dose, respectively. The Mor and Mor-SO concentration ranges in plasma for 9 arrhythmic patients after 2-wk therapeutic trial were 0.09 +/- 0.07 to 0.9 +/- 0.5 microgram.ml-1 and 0.040 +/- 0.023 to 0.15 +/- 0.06 micrograms.ml-1, respectively. These results suggested that cumulative doses would not result in accumulation of the drug and the anti-arrhythmic effect of Mor-SO might not be realized.

Adult↗

PubMed1993

20-item neonatal behavioral neurological assessment used in predicting prognosis of asphyxiated newborn.

From January 1989 to June 1990, 13 institutions in our country studied jointly the application of a 20-item neonatal behavioral neurological assessment (NBNA) in asphyxiated babies. Of 145 cases, 125 were followed up to 1-2 years of age. The results showed that in predicting prognosis, the sensitivity and specificity of NBNA score at 7 days after birth were 88.9% and 82.6% and 12-14 days, 84.6% and 97.4% respectively. Its value in predicting prognosis is superior to Sarnat degree, cranial CT and B ultrasound. This method is practical, economical and reliable. It is worth popularizing.

Apgar Score↗

PubMed1992

The sucrose carrier of the plant plasmalemma. III. Partial purification and reconstitution of active sucrose transport in liposomes.

The proteins from plasma membranes from sugar beet leaves were solubilized by 1% CHAPS and separated by size exclusion chromatography and by ion-exchange chromatography. The fractions enriched in sucrose transporter were monitored in three ways: differential labeling, ELISA, and reconstitution in proteoliposomes. When the plasma membranes were differentially labeled by N-ethylamaleimide in the presence of sucrose, a major peak of differential labeling was found at 120 kDa upon gel filtration. When this peak was recovered, denaturated by sodium dodecyl sulfate and reinjected on the gel filtration column, it yielded a peak of differential labeling at 42 kDa. When unlabeled membranes were used, the fractions eluted from the column were monitored by ELISA for their ability to recognize a serum directed against a 42 kDa previously identified as a putative sucrose carrier. The results paralleled those obtained by differential labeling, i.e. a major ELISA-reactive peak was found at 120 kDa upon gel filtration, and this peak yielded a peak most reactive at 40 kDa after denaturation. The 120 kDa peak prepared from unlabeled membranes was further separated on a Mono-Q column. The fractions were monitored by ELISA as described above, and reconstituted into proteoliposomes using asolectin. Active transport of sucrose, but not of valine could be observed with the reconstituted 120 kDa fraction. When the eluates from the Mono-Q column were reconstituted, the fractions exhibiting highest transport activity were enriched with a 42 kDa band. The data provide the first report concerning reconstitution of sucrose transport activity and confirm the involvement of a 42 kDa polypeptide in sucrose transport.

Biological Transport, Active↗

PubMed1992

Influence of outer membrane mutations on susceptibility of Escherichia coli to the dibasic macrolide azithromycin.

Azithromycin differs chemically from erythromycin by having an extra positive charge created by the presence of a methyl-substituted nitrogen in the 15-membered macrolide ring. This results in substantially increased potency against Gram-negative bacteria. Therefore, the possibility was considered that azithromycin was taken across the outer membrane of Escherichia coli by the self-promoted uptake route, which is utilized by other cationic antibiotics including polymyxins and aminoglycosides. Azithromycin, like polymyxin B and gentamicin, demonstrated equal activity against porin-sufficient and porin-deficient E. coli strains but its MIC was increased eight-fold by magnesium supplementation. Nevertheless, an outer membrane-altered mutant DC2 was eight-fold more susceptible than its parent strain UB1005 to azithromycin, indicating that the outer membrane was a permeability barrier to this macrolide. A mutant SC9252 which had an alteration in the self-promoted uptake of polymyxin and gentamicin, was more resistant to azithromycin, polymyxin and gentamicin compared to its parent SC9251. Further azithromycin, like polymyxin B and gentamicin, was capable of weakly permeabilizing cells to the hydrophobic fluorophor 1-N-phenyl-naphthylamine, a process antagonized by Mg2+. The monobasic macrolide erythromycin on the other hand was less affected by the SC9252 mutation, less effectively antagonized by Mg2+, and was a far less effective permeabilizer than dibasic azithromycin. These data are consistent with the hypothesis that the improved efficacy of azithromycin compared to erythromycin against E. coli reflects its better access to the self-promoted uptake pathway due to its additional positive charge.

Azithromycin↗

PubMed1992

Nitric oxide synthase immunoactivity and NADPH diaphorase enzyme activity in neurons of the gastrointestinal tract of the toad, Bufo marinus.

The presence of nitric oxide synthase (NOS) was demonstrated immunohistochemically, and NADPH diaphorase was demonstrated by enzyme histochemistry in neurons throughout the gastrointestinal tract of the anuran amphibian, Bufo marinus. Successive staining showed that NOS immunoreactivity and NADPH diaphorase activity occurred in precisely the same subgroup of enteric neurons. Subsequent detailed studies of the distribution of these neurons were made using NADPH diaphorase histochemistry. Numerous reactive nerve cell bodies and fibres were found in the myenteric plexus from the esophagus to the cloaca. A dense innervation of the longitudinal and circular muscle layers occurred throughout the gastrointestinal tract. The lamina muscularis mucosae was only prominent in the stomach, where it was sparsely innervated. Reactive nerve cell bodies were common in the submucosa of the large intestine, less common in the small intestine and extremely rare in the stomach and esophagus. Reactive fibres contributed to subepithelial plexuses in the esophagus, colon, rectum and cloaca. It is concluded that NOS/NADPH diaphorase is conserved amongst vertebrate classes and that NO is a likely neurotransmitter in the toad gastrointestinal tract.

Amino Acid Oxidoreductases↗