Biomedical subjects

X L Yang

Publications and source records attributed to X L Yang.

At least 55 records · Page 3Linked to original sources

PubMed2000

[Alteration of the expression of rat cardiac Galphaq/11 and Gialpha2 proteins during endothelin-1 pre-treatment].

The present study was undertaken to explore the mechanism of G protein-mediated signal transduction pathway during endothelin-1 (ET-1) pre-treatment and ischemic preconditioning (IP). Rats were divided into four groups: ET-1, IP, ischaemia-reperfusion (IR) and control groups. ET-1 pre-treatment model was prepared by administrating 0.5 nmol/(L.kg) ET-1 into rat left ventricle, whereas IP model was prepared by ligating the left coronary artery for 5 min followed by 30 min reperfusion. All the animals were subjected to 60 min regional ischaemia and 30 min reperfusion alternately and then parameters of ventricular arrhythmia and expression of cardiac Galphaq/11 and Gialpha2 were measured. The results showed that the scores of ventricular arrhythmia decreased significantly in both ET-1 and IP treated groups as compared with IR group. In comparison with control group, Galphaq/11 increased by 77.8% (P<0.05) and 110.6% (P<0.01) in IP and ET-1 group respectively. Gialpha2 showed no significant difference in IP group, while it decreased by 31.0% (P<0.01) in ET-1 group. In conclusion, activation of G alphaq/11 may be related to the protecting mechanism of ET-1 pre-treatment and IP, whereas Gialpha2 may only play a role in ET-1 pre-treatment.

Animals↗

PubMed2000

[Extraction and separation of antitumor components from Ganoderma lucidum (Leyss. ex Fr.) Karst].

OBJECTIVE: To examine the variation of alcohol extraction rates of Ganoderma lucidum spores with different rates of wall-wrack, and analyze the antitumor components of alcohol extract by chromatography. METHOD: The G. lucidum spores were soaked and extracted with absolute alcohol. The alcohol extract was chromatographed on a silica gel column and HPLC in proper order, and the antitumor activity of every eluted fraction was represented by its cytotoxicity towards Hela cells. RESULT: Extraction rates 5%, 25% and 33% corresponded to wall-wrack rates 0%, 60%-80% and 99% respectively. The alcohol extract from spores with the highest wall-wrack rate was chromatographed on a silica gel column, eluting successfully with CHCl3, EtOAc and CH3OH in order. The CHCl3 fraction had not any antitumor activity, while this activity of CH3OH fraction was 34 times greater than that of EtOAc fraction. HPLC analysis found out that two mixtures(II1 and II3) possess significant antitumor activity in vitro. CONCLUSION: The weight of alcohol extract from spores with wall-wrack was far greater than that of spores without. The antitumor components of G. lucidum spores could be analyzed with methanol-water on a reverse HPLC.

Antineoplastic Agents, Phytogenic↗

PubMed2000

[Recent advances of silica packing in high performance liquid chromatography].

Developments of silica packings in high performance liquid chromatography are reviewed with 65 references. Preparative and modification methods of silica packings are introduced. The physical characterization on silica surface is elucidated. The applications of silica packings in HPLC are outlined and the trends of silica packings in China are described.

Chemical Phenomena↗

PubMed1999

Imidazole-imidazole pair as a minor groove recognition motif for T:G mismatched base pairs.

The T:G mismatched base pair is associated with many genetic mutations. Understanding its biological consequences may be aided by studying the structural perturbation of DNA caused by a T:G base pair and by specific probing of the mismatch using small molecular ligands. We have shown previously that AR-1-144, a tri-imidazole (Im-Im-Im) minor groove binder, recognizes the sequence CCGG. NMR structural analysis of the symmetric 2:1 complex of AR-1-144 and GAACCGGTTC revealed that each AR-1-144 binds to four base pairs with the guanine N2 amino group forming a bifurcated hydrogen bond to a side-by-side Im/Im pair. We predicted that the free G-N2 amino group in a T:G wobble base pair can form two individual hydrogen bonds to a side-by-side Im/Im pair. Thus an Im/Im pair may be a good recognition motif for a T:G base pair in DNA. Cooperative and tight binding of an AR-1-144 homodimer to GAACTGGTTC permits a detailed structural analysis by 2D NOE NMR refinement and the refined structure confirms our prediction. Surprisingly, AR-1-144 does not bind to GAATCGGTTC. We further show that both the Im-Im-Im/Im-Py-Im heterodimer and the Im-Im-Im/Im-Im-Im homodimer bind strongly to the CACGGGTC + GACTCGTG duplex. These results together suggest that an Im/Im pair can specifically recognize a single T:G mismatch. Our results may be useful in future design of molecules (e.g. linked dimers) that can recognize a single T:G mismatch with specificity.

Base Pair Mismatch↗

PubMed1999

Zn2+ differentially modulates kinetics of GABA(C) vs GABA(A) receptors in carp retinal bipolar cells.

GABA(C) and GABA(A) receptors co-exist in retinal bipolar cells. In the present study the effects of zinc on the kinetics of currents mediated by GABA(C) and GABA(A) receptors were investigated in isolated carp bipolar cells, using whole-cell patch-clamp technique. We observed for the first time that zinc exerted opposite effects on kinetics of the GABA(C) and GABA(A) responses: zinc significantly slowed down activation and desensitization of the GABA(C) response, but accelerated those of the GABA(A) response; zinc dramatically accelerated deactivation of the GABA(C) response, whereas it had no apparent effect on deactivation of the GABA(A) response. These results suggest that zinc may be functionally important in regulating retinal signal transmission.

Animals↗

PubMed1999

Zn2+ differentially modulates glycine receptors versus GABA receptors in isolated carp retinal third-order neurons.

It was previously reported that strychnine-sensitive glycine receptors and GABAA receptors co-existed on carp retinal third-order neurons (amacrine/ganglion cells) (Li, P. and Yang, X.-L., Strong synergism between GABAA and glycine receptors on isolated carp third-order neurons. NeuroReport, 9 (1998) 2785-2789.). In this study, the effects of the divalent cation Zn2+ on these two receptors were studied in amacrine/ganglion cells acutely isolated from carp, with the use of the whole-cell patch clamp recording technique. The glycine-induced currents were steadily potentiated by Zn2+ of lower concentrations (0.1-10 microM), while being dose-dependently inhibited by Zn2+ of higher concentrations ( > 100 microM). Both the effects involved changes in apparent glycine affinity of the glycine receptor. In contrast, Zn2+ consistently suppressed the GABA(A) mediated currents of these cells, and did not show similar dual effect. The differential modulation by Zn2+ of glycine receptors versus GABA(A) receptors provides a versatility for regulating inhibitory glycinergic and GABAergic inputs converging on most amacrine/ganglion cells.

Animals↗

PubMed1999

GABA(B) receptors in Müller cells of the bullfrog retina.

GABA is a major inhibitory neurotransmitter in the vertebrate retina. Using GABA(B) receptor-specific antibody combined with glial fibrillary acidic protein (GFAP) antiserum, we demonstrated that primary processes, vitreal endfeet and somata of virtually all Müller glial cells in the bullfrog retina prominently showed GABA(B) receptor immunoreactivity by light and electron microscopy. This study provides the first evidence that glial elements in the vertebrate retina express GABA(B) receptors. Such receptors on Müller cells may play an important role in retinal information processing through regulating the conductance of the inward-rectifying K+ channels.

Animals↗

PubMed1999

Differential expression of the lysosome-associated membrane proteins in normal human tissues.

The lysosome-associated membrane proteins LAMP-1 and LAMP-2 have closely related structures, with 37% sequence homology, and are major constituents of the lysosomal membrane. Their roles are unknown, but they are thought to be structural or functional components of the lysosomal membrane. Recent reports suggest that despite their similar structure and common localization, LAMP-1 and LAMP-2 may have different functions. In our further study of these two molecules, the presence of LAMP-1 and LAMP-2 in a variety of human tissues was analyzed by immunohistochemistry, and their localization was compared to that of cathepsin D, a lysosomal hydrolase. the tissue content of LAMP-1 and LAMP-2 and their respective mRNAs were also analyzed by Northern and Western blotting. The LAMP molecules were detected by immunohistochemistry primarily in metabolically active cells, with a cytoplasmic distribution similar to that of cathepsin D and consistent with their predominant localization in lysosomes. However, there were marked differences in the intensity of staining and, in some cases, the localization of the three proteins. For example, there was much stronger staining for LAMP-2 than LAMP-1 in brain tissue and prostate ductal cells. These differences in localization were consistent with the results obtained in Western blotting of protein extracted from the tissues. The pattern of mRNA expression was similar in all of the examined tissues, with a single mRNA identified for LAMP-1 and two splice variant forms seen for LAMP-2. Our studies of these molecules in human tissues support the conclusion that the expression of the molecules is independently controlled in some tissues, suggesting that the molecules may have independent as well as similar functions.

Antigens, CD↗

PubMed1999

Biliary excretion of copper in LEC rat after introduction of copper transporting P-type ATPase, ATP7B.

Wilson's disease, an autosomal recessive disorder, is characterized by the excessive accumulation of hepatic copper that results from reduced biliary copper excretion and disturbed incorporation of copper into ceruloplasmin. The ATP7B gene, responsible for the disease, encodes a copper transporting P-type ATPase. We previously demonstrated the involvement of ATP7B in hepatic copper secretion into plasma after the introduction of ATP7B into the Long-Evans Cinnamon (LEC) rat, a rodent model of Wilson's disease. In this study we found the increased copper contents of the hepatic lysosomal fractions and bile in the LEC rats after ATP7B introduction, indicating the participation of ATP7B in the biliary excretory pathway for copper.

Adenosine Triphosphatases↗

PubMed1999

Zinc modulation of AMPA receptors may be relevant to splice variants in carp retina.

With the use of the whole-cell patch clamp technique, we examined effects of zinc on AMPA receptors of isolated carp retinal horizontal cells, predominantly consisting of flop splice variants. We found that zinc ranging from 30 microM to 1 mM failed to modulate glutamate-induced currents of these cells, which is clearly distinct from the results previously obtained in superior colliculus neurons and Xenopus ooctyes. Furthermore, glutamate responses remained unchanged when zinc was co-applied with PEPA, a flop variant-preferential AMPA receptor potentiator. With the co-application of cyclothiazide, a flip variant-preferential AMPA receptor potentiator, however, a dual effect could be observed: zinc potentiated glutamate responses at low concentrations, but inhibited them at higher concentrations. These results suggest that the action of zinc on AMPA receptors may be splice variant-relevant.

Animals↗

PubMed1999

Structural studies of atom-specific anticancer drugs acting on DNA.

The interactions of many important anticancer drugs with DNA play important roles in their biological functions. In fact, DNA can be considered as a macromolecular receptor for those drugs. There are several classes of DNA-acting anticancer drugs. Some form noncovalent complexes with DNA by either intercalation (such as daunorubicin and doxorubicin) or groove-binding (such as distamycin A). Others, such as cisplatin, mitomycin C, and ecteinascidins, form covalent linkages with DNA. Finally, some (e.g., duocarmycin/CC-1065, bleomycin/pepleomycin, and enediyne antibiotics) cause DNA backbone cleavages. During the past decade, the detailed molecular interactions of several DNA-acting anticancer drugs with DNA have been studied with structural tools, including high resolution X-ray diffraction and NMR spectroscopy. These results have provided useful insights into DNA conformation and drug-DNA interactions. In particular, it was found that specific atomic sites on DNA are often the targets for drug covalent actions. Here we review the structural aspects of the interactions of several anticancer drugs acting on: (1) the N2 amino group of guanine in the minor groove, (2) the N3 atom of guanine and adenine in the minor groove, (3) the N7 atom of guanine and adenine in the major groove, and finally, (4) the C4', C5', and C1' atoms of the deoxyribose in the backbone of B-DNA double-helix. Understanding the underlying mechanism of the drug action at the cellular and molecular levels through those structural studies should be useful in the development of new anticancer drugs.

Adenine↗

PubMed1999

Modulation of desensitization at glutamate receptors in isolated crucian carp horizontal cells by concanavalin A, cyclothiazide, aniracetam and PEPA.

In horizontal cells freshly dissociated from crucian carp (Carassius auratus) retina, we examined the effects of modulators of glutamate receptor desensitization, concanavalin A, cyclothiazide, aniracetam and 4-[2-(phenylsulfonylamino)ethylthio]-2,6-difluoro-phenoxyacetam ide (PEPA), on responses to rapid application of glutamate and kainate, using whole-cell voltage-clamp techniques. Incubation of concanavalin A suppressed the peak response but weakly potentiated the equilibrium response of horizontal cells to glutamate. Cyclothiazide blocked glutamate-induced desensitization in a dose-dependent manner, which resulted in a steady increase of the equilibrium current. The concentration of cyclothiazide causing a half-maximal potentiation for the equilibrium response was 85 microM. Furthermore, cyclothiazide shifted the dose-response relationship of the equilibrium current to the right, but slightly suppressed the kainate-induced sustained current. These effects of concanavalin A and cyclothiazide are consistent with the supposition that glutamate receptors of carp horizontal cells may be an alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA)-preferring subtype. In order to further characterize the AMPA receptors of horizontal cells, modulation by aniracetam and PEPA of glutamate- and kainate-induced currents was studied. Aniracetam, a preferential modulator of flop variants of AMPA receptors, considerably blocked desensitization of glutamate-induced currents, but only slightly potentiated kainate-induced currents. It was further found that PEPA, a flop-preferring allosteric modulator of AMPA receptor desensitization, slightly suppressed the peak current, while it dramatically potentiated the equilibrium current induced by glutamate in a dose-dependent manner. PEPA was much potent than aniracetam at these receptors and showed the effect on glutamate-induced desensitization even at a concentration as low as 3 microM. PEPA also potentiated non-desensitizing currents induced by kainate, but with much less extent. These modulatory effects of concanavalin A, cyclothiazide, aniracetam and PEPA on AMPA receptors in carp horizontal cells were rather similar to those obtained at AMPA receptors assembled from flop variants expressed in Xenopus oocyte and HEK cell. Consequently, we speculate that the AMPA receptor on carp horizontal cells may predominantly carry the flop splice variants.

Animals↗

PubMed1999

Binding of AR-1-144, a tri-imidazole DNA minor groove binder, to CCGG sequence analyzed by NMR spectroscopy.

The interactions of N-[2-(dimethylamino)ethyl]-1-methyl-4-[1-methyl-4-[4-formamido-1-meth ylimidazole-2-carboxamido]imidazole-2-carboxamido]imidazole-2-c arboxa mide (AR-1-144), a tri-imidazole polyamide minor groove binder, with DNA have been investigated by NMR and CD spectroscopy. A series of DNA oligonucleotides with a C/G-containing four-bp core, i.e. CCGG, CGCG, GGCC, and GCGC, have been titrated with AR-1-144 at different ratios. AR-1-144 favors the CCGG sequence. The flanking sequence of the CCGG core also influences the binding preference, with a C or T being favored on the 3'-side of the CCGG core. The three-dimensional structure of the symmetric 2:1 side-by-side complex of AR-1-144 and GAACCGGTTC, determined by NOE-constrained NMR refinement, reveals that each AR-1-144 binds to four base pairs, i.e. at C5-G6-G7-T8, with every amide-imidazole unit forming two potential hydrogen bonds with DNA. The same DNA binding preference of AR-1-144 was also confirmed by circular dichroism spectroscopy, indicating that the DNA binding preference of AR-1-144 is independent of concentration. The cooperative binding of an AR-1-144 homodimer to the (purine)CCGG(pyrimidine) core sequence appears to be weaker than that of the distamycin A homodimer to A/T sequences, most likely due to the diminished hydrophobic interactions between AR-1-144 and DNA. Our results are consistent with previous footprinting data and explain the binding pattern found in the crystal structure of a di-imidazole drug bound to CATGGCCATG.

Base Sequence↗

PubMed1999

Characterization of AMPA receptors on isolated amacrine-like cells in carp retina.

In amacrine-like cells freshly dissociated from crucian carp (Carassius auratus) retina, we recorded whole-cell responses to rapid application of glutamate and kainate. Currents induced by glutamate, but not kainate, usually showed extremely rapid desensitization, and the mean time constant for the decay of the responses to 10 mM glutamate was 2.77 ms. N-methyl-D-aspartate (NMDA) failed to induce any current even with coapplication of glycine and removal of extracellular Mg2 +. 1-(4-aminophenyl)-3-Methylcarbamyl-4-methyl-7,8-methylenedioxy-3, 4-dihydro-5H-2,3-benzodiazepine (GYKI 53655), a selective alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor antagonist, was found to completely block glutamate-induced currents, suggesting that the glutamate receptors on these cells are AMPA preferring. The value of EC50 for glutamate and kainate was determined to be 2.73 mM and 97.5 microM, respectively. Noise analysis of fluctuation of whole-cell currents induced by kainate of different concentrations indicated that the mean conductance of the AMPA receptor channels was 5.70 pS. Splice variant analysis of the AMPA receptors was also conducted by comparing the effects of cyclothiazide, a flip receptor-preferring modulator and 4-[2-(phenylsulphonylamino)ethylthio]-2,6-difluoro-phenoxyaceta mide (PEPA), a flop receptor-preferring modulator, on glutamate-induced responses. PEPA was much more potent than cyclothiazide at these receptors with a EC50 of 17.3 microM. The mean ratio of the potentiation by PEPA versus cyclothiazide (P/C ratio) was 4.39. These modulatory effects of cyclothiazide and PEPA were rather similar to those obtained at AMPA receptors assembled from flop variants expressed in Xenopus oocytes, suggesting that the AMPA receptor of the carp amacrine cells may predominantly consist of the flop splice variants.

Alternative Splicing↗

PubMed1999

Glucose and amino acid kinetic response to graded infusion of rhIGF-I in the late gestation ovine fetus.

Insulin-like growth factor I (IGF-I) has anabolic effects and is thought to be important in fetal development. The present study was designed to determine the dose response of recombinant human (rh) IGF-I on ovine fetal glucose and amino acid kinetics. Chronically catheterized fetal lambs were studied at 122-127 days gestation. The kinetics of leucine, phenylalanine, and glucose were measured before and during the infusion of rhIGF-I. rhIGF-I was infused into the fetal inferior vena cava at low, medium, or high rates (9.9, 20.1, or 40.2 nmol/h, respectively). A stepwise increase in serum IGF-I was achieved (164 +/- 3, 222 +/- 7, and 275 +/- 5 ng/ml). Insulin concentrations were decreased at the medium and high rhIGF doses. The rate of appearance (Ra) of leucine and phenylalanine and leucine oxidation decreased. Phenylalanine appearance from protein breakdown was decreased, with a maximal suppression of 30% observed at the highest rate of infusion. Glucose Ra was increased at the medium and high doses; other aspects of glucose metabolism were unchanged. The change in both glucose Ra and suppression of proteolysis was significantly correlated to the rhIGF-I infusion rate. It is concluded that rhIGF-I exerts dose-related effects in the ovine fetus, increasing fetoplacental glucose turnover and causing significant suppression of both proteolysis and amino acid oxidation.

Amino Acids↗

PubMed1999

Perinatal hypoxia-ischemia decreased neuronal but increased cerebral vascular endothelial IGFBP3 expression.

In adults, insulin-like growth factor binding protein 3 (IGFBP3) is the main carrier protein for circulating insulin-like growth factors (IGFs) (IGF-I and -II). While most IGFBP3 is synthesized in the liver, it is also expressed locally by many cell types including vascular endothelial cells. The regulation of this endothelial IGFBP3 expression, especially in response to hypoxic-ischemic injury, has not been investigated in vivo. Using in situ hybridization histochemistry, we studied the cellular distribution of IGFBP3 mRNA in rat brains following hypoxic-ischemic injury at 1, 5, 24, and 72 h of recovery. In normal P7 rat brain, IGFBP3 mRNA was found in neurons within the thalamus, hippocampus, and amygdaloid. Low levels of IGFBP3 mRNA were also detected in cerebral vascular endothelial cells. After the hypoxic-ischemic injury, the levels of neuronal IGFBP3 mRNA substantially decreased within 24 h in areas that were normally supplied by the middle cerebral artery. In the meantime, there was an immediate increase in IGFBP3 expression in vascular endothelial cells throughout the affected hemisphere. This vascular IGFBP3 expression was further enhanced with the highest level at 24 h of recovery whereas neuronal IGFBP3 expression was further decreased. By 72 h of recovery, IGFBP3 was no longer expressed in vascular endothelial cells. Taken together, the activation of IGFBP3 is a likely mechanism by which vascular endothelial cells respond to hypoxic-ischemic insult. In addition, increased endothelial IGFBP3 may modulate the interaction of IGFs with IGF-I receptors at the site of injury and/or act independently on endothelial cell growth.

Animals↗

PubMed1999

Alteration of IGF system gene expression during the postnatal development of pcd mice.

IGF-I promotes growth during postnatal development via both endocrine and autocrine actions. In pcd mice (pcd/pcd), we previously found that IGF-I mRNA expression was decreased in cerebellar Purkinje cells as they underwent apoptosis. To investigate the endocrine function of IGF-I, we examined hepatic IGF-I mRNA by Northern hybridization, circulating IGF-I peptide by radioimmunoassay, and circulating IGFBP by Western ligand blot in pcd mice. At postnatal days (D) 17 and 24, hepatic IGF-I mRNA and circulating IGF-I and IGF-II concentrations were normal in pcd mice. From D45, both hepatic IGF-I mRNA and circulating IGF-I concentrations decreased. The decrease in circulating IGF-I concentrations was accompanied by a simultaneous increase in circulating IGF-II concentrations in both the D45 and adult pcd mice. An early decrease in the circulating IGFBP-3 levels and an increase in the IGFBP-2 levels were observed at D17 and were followed by decreases in both IGFBPs at D45 and in the adult. Therefore, after the cerebellar neurodegeneration, there was an overall decrease in IGF-I gene expression in pcd mice. Our results suggest that the decrease in IGF-I gene expression may contribute to growth deficiency and multiple system degeneration in pcd mice.

Animals↗

PubMed1999

Projections from subnucleus oralis of the spinal trigeminal nucleus to contralateral thalamus via the relay of juxtatrigeminal nucleus and dorsomedial part of the principal sensory trigeminal nucleus in the rat.

Following injection of HRP into contralateral thalamus, retrogradely labeled cells were observed in principal sensory trigeminal nucleus (Vp) and an area of juxtatrigeminal nucleus (JX) formerly described by John and Tracey (1987). When PHA-L was delivered to dorsomedial part of the subnucleus oralis (Vodm), PHA-L labeled terminals were seen in dorsomedial part of the Vp (Vpdm) and in the JX region. Comparing the distribution of PHA-L labeled terminal field with that of HRP labeled JX neurons showed that the labeled terminals and neurons were overlapped closely in the JX. The distribution patterns of the labeled terminals and JX neurons were also the same: viewed on the coronal planes caudal-rostrally, both of the labelings began to appear at the levels where the facial nerve root was just broken. Rostrally, at middle levels of the motor trigeminal nucleus (Vmo), the labelings showed their typical view covering dorsal and ventral JX (dJX, vJX). The labelings disappeared at rostral poles of the Vmo and Vp. When injections of PHA-L into the Vodm and HRP into the contralateral thalamus was made in one rat, the contacts between Vodm projecting terminals labeled with PHA-L and HRP labeled trigemino-thalamic neurons were seen in the JX and also in the Vpdm. Then, electron microscopic (EM) study was done, injections of kainic acid into the Vodm and HRP into the contralateral thalamus was performed simultaneously. After EM embedding, the JX and Vpdm regions were selected, ultrathin sections were cut and observed with EM. In both areas, axo-somatic and axo-dendritic synapses were seen between degenerated boutons and HRP labeled somata or dendrites. Namely, the Vodm projecting terminals synapsed on trigemino-thalamic neurons in the JX and Vpdm. Anyway, axo-dendritic synapses was the main type of observed synapses. Thus, the present work demonstrated 1. the JX containing a group of trigemno-thalamic neurons was a target of special projections froin the Vodm; 2. The Vodm neurons projected to the contralateral thalamus through the relay of JX and Vpdm neurons.

Animals↗