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H Liu

Publications and source records attributed to H Liu.

At least 883 records · Page 49Linked to original sources
PubMed1997

Tyrosine kinases modulate the activity of single L-type calcium channels in vascular smooth muscle cells from rat portal vein.

In a previous study, we demonstrated that extracellular application of the tyrosine kinase inhibitor genistein produced a dose-dependent inhibition of the macroscopic slow (L-type) Ca2+ currents of vascular smooth muscle (VSM) cells, and that daidzein, an inactive analog of genistein, had no such effect. These results suggested that the L-type Ca2+ channels in VSM cells may be modulated by endogenous tyrosine kinase activity. To confirm and extend those findings, the effect of genistein on the activity of single Ca2+ channels was examined in freshly isolated single VSM cells from rat portal vein, using the cell-attached patch-clamp technique. The pipette solution contained 90 mM Ba2+ as charge carrier and 0.5 microM Bay K 8644 (to enhance basal activity of the channels), and the bath contained 140 mM KCl to "zero" the resting membrane potential. Depolarizing pulses to 0 mV, from a holding potential of -80 mV, elicited inward unitary currents that were blocked by 1 microM nifedipine (n = 6). The slope conductance of the unitary Ca2+ currents gave a value of 21.5 +/- 0.4 pS (n = 9) for the Ca2+ channels. Bath application of genistein (50 microM) did not change the unit amplitude and slope conductance: the conductance in the presence of genistein was 22.2 +/- 0.5 pS (n = 6). However, compared with controls, the activity of single Ca2+ channels was significantly inhibited by genistein in a dose-dependent fashion. The ensemble-averaged currents were decreased by 48.4 +/- 11.2% with 50 microM genistein; 100 microM genistein inhibited the Ca2+ currents by 76.8 +/- 11.8%. The open probability (NPo) was decreased by 50 microM genistein from 0.24 +/- 0.09 to 0.11 +/- 0.07. Single-channel kinetic analysis showed that genistein decreased the mean open time and prolonged the mean closed time. The inhibitory effect of genistein on the Ca2+ channel activity occurred within 3 min, and it could be reversed by washout within 3-5 min. Daidzein, in concentrations up to 300 microM, produced no change in the activity of the single Ca2+ channels. These results demonstrate that genistein inhibits the activity of the L-type Ca2+ channels in VSM cells, suggesting that the availability of the channels for voltage activation may be maintained through tonic tyrosine kinase phosphorylation.

Animals↗
PubMed1997

Understanding species-specific differences in substrate recognition by Escherichia coli and human prolyl-tRNA synthetases.

Class II human prolyl-tRNA synthetase (ProRS) aminoacylates in vitro transcribed human tRNA(Pro) with kinetic parameters that are similar to those previously determined for aminoacylation of Escherichia coli tRNA(Pro) by its cognate synthetase. As in the bacterial system, large decreases in aminoacylation by human ProRS occur upon mutating anticodon positions G35 and G36 of human tRNA(Pro). The N73 'discriminator' base and the first and third base pairs of the acceptor stem vary between the E.coli and human isoacceptor groups. In contrast to the E. coli synthetase, the human enzyme does not appear to recognize these elements, since mutations at these positions do not significantly affect cognate synthetase charging. E. coli ProRS does not cross-aminoacylate human tRNA(Pro), and the bacterial tRNA(Pro) is a poor substrate for the human enzyme. Mutations in both the tRNAs and the synthetases have been made in an effort to identify elements in each system responsible for blocking cross-species aminoacylation. Alignment of all known ProRS primary sequences from different species reveals particularly low overall sequence homology, as well as two distinct groups of enzymes. The sequence divergence between E. coli and human ProRSs helps to explain the species-specific differences in the RNA code for aminoacylation of tRNA(Pro).

Amino Acid Sequence↗
PubMed1997

Border malaria in Yunnan, China.

Yunnan Province, due its international borders with Myanmar, Vietnam and Lao PDR has a large number of imported cases of malaria, including a high proportion of Plasmodium falciparum, as a result of the mobility of the population. This movement is due to workers coming from other provinces where there is no malaria to work in the productive tropical lowlands. Chinese nationals who have gone to work in neighboring countries, border trade and refugees from Myanmar. Much of Yunnan is peopled by ethnic minorities living in remote mountainous and forested areas which are difficult to reach. However, surveillance has been strengthened by training 3,900 primary health care workers and combining the search for visiting foreigners, returning Chinese and people from other provinces with public security, customs formalities and employers. Any visitor detected by these services is obliged to have a blood slide taken. This has resulted in an earlier and more complete detection of malaria cases, reducing incidence from 19.19 to 12.12/10,000 in the border area over the last 10 years. This is despite a considerable increase in population movement and the threat of drug resistant malaria.

China↗
PubMed1997

Polymorphisms of vitamin D receptor gene and its association with bone mineral density and osteocalcin in Chinese.

OBJECTIVE: To explore the distribution frequencies of vitamin D receptor (VDR) gene polymorphisms in Chinese and the relationship between VDR genotypes and bone mineral density (BMD) or serum osteocalcin level in Chinese women. METHODS: Polymorphisms of VDR gene were analyzed by polymerase chain reaction (PCR) to amplify the DNA sequence and three restriction enzymes (namely BsmI, ApaI and TaqI) to digest the PCR products in 223 subjects. Some of the VDR genotypes were also confirmed by Southern hybridization analysis. BMD was measured at the spine and proximal femur by dual-energy X-ray absorptiometry (DEXA). Serum osteocalcin concentrations were determined by radioimmunoassay. RESULTS: Chinese had high frequencies of "b,a,T" alleles, 95%, 75% and 95% respectively, which were much different from Caucasians. "BB" or "AA" genotype had tendency for higher BMD at some sites in the group of young women, whereas in the group of postmenopausal women, "bb" or "aa" genotype had relationship with lower BMD at femoral neck and trochanter. Furthermore, no relationship were found between VDR genotypes and the serum osteocalcin level in Chinese women. CONCLUSIONS: Allele frequencies of VDR gene in Chinese are different from those in Caucasians. VDR gene polymorphisms are associated with BMD in Chinese, but in a different pattern from other reports. Further study on predicting function of VDR for osteoporosis is necessary.

Adult↗
PubMed1997

[Protective effect of magnesium on ionic channels in guinea pig ventricular myocytes during hypoxia].

OBJECTIVE: To determine effects of Mg2+ on potassium current, transient inward current (Iti) and Na(+)-Ca2+ exchange current in isolated ventricular myocytes during hypoxia. METHODS: Single myocytes were isolated from ventricles of adult guinea pig hearts. The patch clamp technique in whole cell configuration was used to study ionic currents, and experiments were performed in an experimental chamber that allows the cell to be exposed to a sufficiently low O2 pressure. RESULTS: The 10 mmol/L intracellular free Mg2+ (Mg2+i) had no effect on action potential abbreviation under normoxic condition, however, the action potential abbreviation during hypoxia was markedly inhibited in presence of 10 mmol/L Mg2+i. The amplitude of hypoxia-induced time independent outward K+ current was also greatly reduced when applied 10 mmol/L Mg2+ in pipette solution. In early reoxygenation, Iti occurred in 73% of myocytes, 10 mmol/L extracellular Mg2+ during hypoxia and reoxygenation lowered incidence of Iti, 10 mmol/L Mg2+ could partly inhibit the Na(+)-Ca2+ exchange current in normoxic condition. CONCLUSION: Intracellular Mg2+ could block hypoxia-induced outward current through ATP sensitive potassium channels. Mg2+i plays an important role in preventing depletion of cellular K+ and regulates beat-to-beat cardiac activity. Extracellular Mg2+ most probably decreases the signs of calcium overload in early reoxygenation by inhibiting Na(+)-Ca2+ exchange.

Animals↗
PubMed1997

[New species of Natronobacterium].

An extreme haloalkalophilic bacterium HAM-2 with pleomorphic rods was isolated from Hamatai soda lake in Inner Mongolia Autonomous Region. Growth occurs in 12%-30% NaCl, no growth below 12%, optimum 17.5%. pH range for good growth 7.8-10.4, optimum 9.0-9.5. The strain HAM-2 is non-motile, Gram-negative, pleomorphic, cell of which were 1.0-2.0 by 2.0-5.0 microns in size in liquid medium. The major polar lipids of the organisms are phosphatidylglycerol phosphate and phosphatidyglycerol and contains an unidentified phospholipid as a minor component PL4. G + C contant of DNA is 59.5 mol%. Based on the characteristics, the strain HAM-2 could be included in the genus Natronobacterium, but since HAM-2 differs from reported four species of this genus in cell shape, polar lipids and biochemical features. The name Natronobacterium innemongoliae sp. nov. is proposed. The type strain is designated HAM-2.

Natronobacterium↗
PubMed1997

[Reconstruction of cervical stability following old facet dislocation of cervical spine].

A total of 12 cases of old facet dislocations of cervical spine treated between december 1988 and 1993 were analyzed in order to evaluate the efficacy of various surgical modalities. In this series, there were 8 males and 4 females, with ages ranged from 16 to 50 years old (averaged 37.8 years old). The duration from injury to admission to our hospital was ranged from 1 to 8 months (averaged 3.7 months). Dislocation levels were as follows: C3,4 in 1 case, C4,5 in 4 cases, C5,6 in 4 cases and C6,7 in 3 cases. Unilateral facet dislocation was in 7 cases and bilateral facet dislocation in 5 cases. Neurological status on admission was as follows: spinal cord and nerve root lesion in 5 cases, nerve root lesion alone in 5 cases and neurologically intact in 2 cases. Besides all facets receiving facetectomy and iliac bone graft, other four kinds of adjuvant treatments were used, including internal fixation by stainless wires laminae or spinous processes in 4 cases, Luque rod in 1 cases, anterior fibrolysis combined with posterior laminoplasty in 1 cases and sustained skull traction without internal fixation in 6 cases. The reduction efficacy from postoperative stustained skull traction was better and the stainless wires fixation ranked the next. The patients only suffering from the nerve root lesion recovered better, but those who had spinal cord combined with nerve root lesion recovered badly. In conclusion, for the treatment of old facet dislocation, it is necessary to resect the facet and graft with iliac bone.

Adolescent↗
PubMed1997

[A study on the infiltration of macrophages and lymphocytes in interrenal tissues in patients with acute renal tubulointerstitial disease].

Renal tissues of 14 patients with acute renal tubulointerstitial disease were studied by using immunohistochemical method. Cells infiltrated in interrenal tissue were observed. The results show that the causes which result in acute renal tubulointerstitial disease are different; the renal tubular and interstitial damages are reversible or irreversible; the major inflammatory cells infiltrated in interrenal tissues are CD68 and CD45ro positive cells. The results suggest that the macrophages and T lymphocytes infiltrated in interrenal tissues play an important role in the progress of acute renal tubulointerstital disease.

Acute Disease↗
PubMed1996

Expression and subunit interaction of voltage-dependent Ca2+ channels in PC12 cells.

Nerve growth factor (NGF)-induced differentiation in PC12 cells is accompanied by changes in the expression of voltage-dependent Ca2+ channels. Ca2+ channels are multimeric complexes composed of at least three subunits (alpha1, beta, and alpha2delta) and are involved in neuronal migration, gene expression, and neurotransmitter release. Although attempts have been undertaken to elucidate NGF regulation of Ca2+ channel expression, the changes in subunit composition of these channels during differentiation still remain uncertain. In the present study, patch-clamp recordings show that in addition to the previously documented L-type and N-type Ca2+ currents, undifferentiated PC12 cells also express an omega-agatoxin-IVA-sensitive (P/Q-type) component. In addition, the corresponding mRNA encoding the pore-forming alpha1 subunits for these channels (C, B, and A, respectively) was detected. Likewise, mRNA for three distinct auxiliary beta subunits (1, 2, 3) were also found, beta3 protein being dominantly expressed. Immunoprecipitation experiments show that the N-type Ca2+ channel is associated with either a beta2 or beta3 subunit and that NGF increases the channel expression without affecting its beta subunit association. These results (1) indicate that the diversity of Ca2+ currents in PC12 cells arise from the expression of three distinct alpha1 and three different beta subunit genes; (2) support a model for heterogenous beta subunit association of the N-type Ca2+ channel in a single cell type; and (3) suggest that the regulation of the N-type Ca2+ channel during NGF-mediated differentiation involves an increase in the number of functional channels with no apparent changes in subunit composition.

Animals↗
PubMed1996

Cadmium increases GLUT1 substrate binding affinity in vitro while reducing its cytochalasin B binding affinity.

Cadmium stimulates glucose transport in fibroblasts, apparently by increasing the intrinsic activity of GLUT1 [Harrison, S.A., Buxton, J.M., Clancy, B.M., & Czech, M.P. (1991) J. Biol. Chem. 266, 19438-19449]. In the present study, we examined whether cadmium affects the binding in vitro of purified GLUT1 to glucose and cytochalasin B. Cadmium inhibited cytochalasin B binding to GLUT1 competitively by reducing its binding affinity with an apparent inhibition constant of approximately 0.2 mM. However, D-glucose displaced cytochalasin B bound to GLUT1 as effectively in the presence of cadmium as in its absence, and detailed analysis of this displacement revealed that cadmium in fact increases the substrate binding affinity significantly. These findings suggest that cadmium induces a specific conformational change in GLUT1 that interferes with cytochalasin B binding but enhances substrate binding. This is the first clear demonstration in which the substrate and cytochalasin B binding activities of GLUT1 are differentially affected, which may offer insight into the workings of the glucose transporter.

Binding, Competitive↗
PubMed1996

Mutations in copper-zinc superoxide dismutase that cause amyotrophic lateral sclerosis alter the zinc binding site and the redox behavior of the protein.

A series of mutant human and yeast copper-zinc superoxide dismutases has been prepared, with mutations corresponding to those found in familial amyotrophic lateral sclerosis (ALS; also known as Lou Gehrig's disease). These proteins have been characterized with respect to their metal-binding characteristics and their redox reactivities. Replacement of Zn2+ ion in the zinc sites of several of these proteins with either Cu2+ or Co2+ gave metal-substituted derivatives with spectroscopic properties different from those of the analogous derivative of the wild-type proteins, indicating that the geometries of binding of these metal ions to the zinc site were affected by the mutations. Several of the ALS-associated mutant copper-zinc superoxide dismutases were also found to be reduced by ascorbate at significantly greater rate than the wild-type proteins. We conclude that similar alterations in the properties of the zinc binding site can be caused by mutations scattered throughout the protein structure. This finding may help to explain what is perhaps the most perplexing question in copper-zinc superoxide dismutase-associated familial ALS-i.e., how such a diverse set of mutations can result in the same gain of function that causes the disease.

Amyotrophic Lateral Sclerosis↗
PubMed1996

p300 is a component of an estrogen receptor coactivator complex.

The estrogen receptor (ER) is a ligand-dependent transcription factor that regulates expression of target genes in response to estrogen in concert with other cellular signaling pathways. This suggests that the mechanism by which ER transmits an activating signal to the general transcription machinery may include factors that integrate these diverse signals. We have previously characterized the estrogen receptor-associated protein, ERAP160, as a factor that complexes with ER in an agonist-dependent manner. We have now found that the transcriptional coactivator p300 associates with agonist bound ER and augments ligand-dependent activation by ER. Our studies show that an ER coactivator complex involves a direct hormone-dependent interaction between ER and ERAP160, resulting in the recruitment of p300. In addition, antibodies directed against the cloned steroid receptor coactivator 1 (SRC1) recognize ERAP160. The known role of p300 in multiple signal transduction pathways, including those involving the second messenger cAMP, suggests p300 functions as a point of integration between ER and these other pathways.

Animals↗
PubMed1996

Expression of rat liver tryptophan 2,3-dioxygenase in Escherichia coli: structural and functional characterization of the purified enzyme.

The hepatic hemoprotein tryptophan 2,3-dioxygenase (TDO) is the key regulatory enzyme that, through irreversible degradation, controls the flux of tryptophan through physiologically relevant pathways. This enzyme is composed of four identical subunits and in its fully assembled tetrameric form requires 2 mol of heme (Fe(+2)-protoporphyrin IX)/mol of protein for functional competence. Using a full-length cDNA for the rat liver TDO subunit (pUC119/TDO) as the template, TDO cDNA was amplified by polymerase chain reaction (PCR) and incorporated into the expression vector pTrc99A after introduction of convenient restriction sites as well as modification of the second codon AGT to GCT to optimize its bacterial expression. DH5 alpha F' strain Escherichia coli cells transfected with this pTrc99A/TDO construct expressed soluble, functionally active, tetrameric TDO protein in high yields. The enzyme was isolated from 30,000g supernatant of cell lysates, purified by ion-exchange chromatography, and its spectral and catalytic properties were assessed in terms of its substrate and prosthetic moiety specificities. In almost all aspects, the bacterially expressed enzyme was found to be identical to that of the rat liver. Heterologous expression of the fully functional enzyme, we trust, will enable future elucidation of its structure-function relationships.

Aminolevulinic Acid↗