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Biomedical subjects

W Li

Publications and source records attributed to W Li.

At least 1,261 records · Page 70Linked to original sources
PubMed1992

Comparison and characterization of retinal pericytes and retinal pigment epithelial cells on subcellular IP3-sensitive Ca2+ pools.

A comparative study of inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ mobilization in bovine retinal capillary pericytes (BRCP) and bovine retinal pigment epithelial cells (BRPE) was carried out. Both cells were permeabilized with saponin. The two cell types had similar basal levels of [Ca2+]i (130 nM for BRCP, 132 nM for BRPE) and responded to IP3 in a dose-dependent manner. However, when stimulated by various concentrations of IP3 (1-10 microM), the increase in [Ca2+]i of BRCP was always two- to threefold higher than that in BRPE. Subcellular-fractionation studies showed that a single population of IP3 binding site with a high affinity and high specificity of IP3 mainly localized to plasma membrane in these two cell types. Although the dissociation constant of specific [32P]-IP3 binding sites (Kd 1.9-2.8 nM) was similar, the profile of maximal binding capacity (Bmax) of each fraction was markedly different. In comparison, plasma membrane fractions of BRCP were with Bmax of 165 fmol/mg protein versus 90 fmol/mg protein for BRPE membranes. The ATP-dependent Ca2+ uptake and IP3-dependent Ca2+ release were observed in the both plasma membrane fractions. With quantitative correlation, the membrane fraction (2 mg) of BRCP released 0.2 nmol Ca2+ whereas BRPE only released 0.07 nmol Ca2+ with the same dose of IP3 (5 microM). The selectively higher density of IP3 binding sites in coupling to the larger Ca(2+)-release in the membrane of BRCP suggests that the quantity of Ca2+ mobilized is determined by the spatially preferential distribution of membrane-associated IP3 binding sites. These findings may provide an explanation for the differences observed between BRCP and BRPE in IP3-induced DNA replication.

Binding Sites↗
PubMed1992

Proline biosynthesis in Saccharomyces cerevisiae: molecular analysis of the PRO1 gene, which encodes gamma-glutamyl kinase.

The PRO1 gene of Saccharomyces cerevisiae encodes the 428-amino-acid protein gamma-glutamyl kinase (ATP:L-glutamate 5-phosphotransferase, EC 2.7.2.11), which catalyzes the first step in proline biosynthesis. Amino acid sequence comparison revealed significant homology between the yeast and Escherichia coli gamma-glutamyl kinases throughout their lengths. Four close matches to the consensus sequence for GCN4 protein binding and one close match to the RAP1 protein-binding site were found in the PRO1 upstream region. The response of the PRO1 gene to changes in the growth medium was analyzed by measurement of steady-state mRNA levels and of beta-galactosidase activity encoded by a PRO1-lacZ gene fusion. PRO1 expression was not repressed by exogenous proline and was not induced by the presence of glutamate in the growth medium. Although expression of the PRO1 gene did not change in response to histidine starvation, both steady-state PRO1 mRNA levels and beta-galactosidase activities were elevated in a gcd1 strain and reduced in a gcn4 strain. In addition, a pro1 bradytrophic strain became completely auxotrophic for proline in a gcn4 strain background. These results indicate that PRO1 is regulated by the general amino acid control system.

Amino Acid Sequence↗
PubMed1992

The SH2 and SH3 domain-containing Nck protein is oncogenic and a common target for phosphorylation by different surface receptors.

Signalling proteins such as phospholipase C-gamma (PLC-gamma) or GTPase-activating protein (GAP) of ras contain conserved regions of approximately 100 amino acids termed src homology 2 (SH2) domains. SH2 domains were shown to be responsible for mediating association between signalling proteins and tyrosine-phosphorylated proteins, including growth factor receptors. Nck is an ubiquitously expressed protein consisting exclusively of one SH2 and three SH3 domains. Here we show that epidermal growth factor or platelet-derived growth factor stimulation of intact human or murine cells leads to phosphorylation of Nck protein on tyrosine, serine, and threonine residues. Similar stimulation of Nck phosphorylation was detected upon activation of rat basophilic leukemia RBL-2H3 cells by cross-linking of the high-affinity immunoglobulin E receptors (Fc epsilon RI). Ligand-activated, tyrosine-autophosphorylated platelet-derived growth factor or epidermal growth factor receptors were coimmunoprecipitated with anti-Nck antibodies, and the association with either receptor molecule was mediated by the SH2 domain of Nck. Addition of phorbol ester was also able to stimulate Nck phosphorylation on serine residues. However, growth factor-induced serine/threonine phosphorylation of Nck was not mediated by protein kinase C. Interestingly, approximately fivefold overexpression of Nck in NIH 3T3 cells resulted in formation of oncogenic foci. These results show that Nck is an oncogenic protein and a common target for the action of different surface receptors. Nck probably functions as an adaptor protein which links surface receptors with tyrosine kinase activity to downstream signalling pathways involved in the control of cell proliferation.

3T3 Cells↗
PubMed1992

Fc epsilon R1-mediated tyrosine phosphorylation of multiple proteins, including phospholipase C gamma 1 and the receptor beta gamma 2 complex, in RBL-2H3 rat basophilic leukemia cells.

In basophils, mast cells, and the RBL-2H3 tumor mast cell line, cross-linking the high-affinity immunoglobulin E receptor (Fc epsilon R1) stimulates a series of responses, particularly the activation of phospholipase C (PLC), that lead to allergic and other immediate hypersensitivity reactions. The mechanism of activation of PLC, however, is not clear. Here, we show that cross-linking Fc epsilon R1 on RBL-2H3 cells causes the tyrosine phosphorylation of at least 12 cellular proteins, including PLC gamma 1 (PLC gamma 1) and the receptor beta and gamma subunits. 32P-labeled PLC gamma 1 can be detected by anti-phosphotyrosine antibody as early as 10 s after the addition of antigen. The tyrosine-phosphorylated 33-kDa beta subunit and 9- to 11-kDa gamma subunit of the Fc epsilon R1 are additionally phosphorylated on serine and theonine residues, respectively, and are found as complexes with other phosphotyrosine-containing proteins in antigen-stimulated cells. Our results indicate a means by which the Fc epsilon R1 may control PLC activity in RBL-2H3 cells and raise the possibility that other receptor-mediated signalling events in mast cells may also be controlled through protein tyrosine phosphorylation.

Animals↗
PubMed1992

Acute cerebral ischemia: evaluation with dynamic contrast-enhanced MR imaging and MR angiography.

Dynamic contrast-enhanced T2-weighted magnetic resonance (MR) imaging and MR angiography (MRA) were used to evaluate cerebral blood volume and the intracranial arterial system in 34 patients within 48 hours after the onset of cerebral ischemia. In 24 of the patients, an abnormality identified on T2-weighted images corresponded to the acute clinical deficit. Intracranial MRA demonstrated occlusions or severe stenoses of major vessels supplying the area of infarction in 16 of these patients, and decreased blood volume correlated well with MRA abnormalities. Infarcts less than 2 cm in diameter were not reliably shown with MRA or blood volume studies. Correlation between lesions seen with MRA and decreased blood volume in acute infarcts was good, and both techniques demonstrated lesions early in the clinical course. By providing information about hemodynamics not available with conventional T1- or T2-weighted images, MRA and dynamic MR imaging could prove helpful in describing the pathophysiologic characteristics of stroke and in guiding early therapeutic intervention.

Adult↗
PubMed1992

Improved time-of-flight MR angiography of the brain with magnetization transfer contrast.

The authors hypothesized that magnetization transfer contrast (MTC) could be used to improve flow contrast in time-of-flight (TOF) magnetic resonance (MR) angiography. Two- and three-dimensional flow-compensated gradient-echo images were obtained with and without MTC. MTC images were obtained by applying low-power radio-frequency (RF) radiation with a frequency offset from the bulk "free" water resonance frequency before the excitation RF pulse. The signal intensity of stationary tissue decreased as the power applied for the MTC pulse was increased. A smaller decrease occurred in venous signal intensity as measured in the superior sagittal sinus, and less change was seen in the arterial signal intensity as measured in the middle cerebral artery. Cerebrospinal fluid showed no MTC effect. The use of MTC improved small-vessel depiction on maximum-intensity projection images. The authors conclude that use of MTC can substantially enhance the quality of TOF MR angiography of the brain.

Adult↗
PubMed1992

Effect of balloon angioplasty on femoral artery evaluated with intravascular ultrasound imaging.

BACKGROUND: Intravascular ultrasound was used to assess the immediate effect of balloon angioplasty on the superficial femoral artery. METHODS AND RESULTS: In 16 consecutive patients, corresponding ultrasonic cross sections (n = 72) before and after balloon angioplasty were qualitatively and quantitatively analyzed. The qualitative data were compared with angiographic findings. Before intervention, the angiographically demonstrated obstructive lesions were confirmed by intravascular ultrasound. Ultrasound enabled discrimination between soft (n = 43) and hard (n = 29) lesions, as well as between eccentric (n = 57) and concentric (n = 15) lesions. After balloon angioplasty, the presence of a dissection assessed angiographically in 14 patients was confirmed by intravascular ultrasound. Additional morphological information provided by ultrasound included plaque rupture in 14 patients and internal lamina rupture in six patients. Quantitative ultrasound data revealed an increase in free lumen area from 9.7 +/- 4.7 to 18.3 +/- 7.0 mm2 (p less than or equal to 0.01), an increase in minimal lumen diameter from 2.8 +/- 0.7 to 3.6 +/- 1.2 mm (p less than or equal to 0.01), and an increase in media-bounded area from 21.7 +/- 5.4 to 28.3 +/- 5.8 mm2 (p less than or equal to 0.01). The lesion area for the majority of cases (n = 32) remained unchanged (13.0 +/- 4.9 mm2 versus 12.9 +/- 4.6 mm2), or the lesion disappeared partially (from 9.1 +/- 0.9 to 4.3 +/- 1.4 mm2, n = 4, p less than or equal to 0.01) or totally (from 10.1 +/- 4.2 to 0 mm2, n = 6). Stretching of the arterial wall was further evidenced by medial thinning from 0.55 +/- 0.19 to 0.34 +/- 0.11 mm (p less than or equal to 0.01). CONCLUSIONS: Luminal enlargement by balloon dilatation is achieved primarily by overstretching the arterial wall, with the lesion volume remaining practically unchanged. Overstretching is accompanied almost always by dissection and plaque rupture and occasionally by an internal lamina rupture.

Aged↗
PubMed1992

Cytosolic free calcium increased by prostaglandin F2 alpha (PGF2 alpha), gonadotropin-releasing hormone, and angiotensin II in rat granulosa cells and PGF2 alpha in human granulosa cells.

Cytosolic [Ca2+]i was measured using a microspectrofluorimetric technique. Prostaglandin F2 alpha (PGF2 alpha, 10(-6) M) transiently increased the concentration of free cytosolic Ca2+ ([Ca2+]i) in individual rat and human granulosa cells. In a study examining a total of 170 individual rat and human granulosa cells, approximately 100% of rat granulosa cells and 80% of human granulosa cells tested responded to PGF2 alpha (10(-6) M). In a dose-response trial, the magnitude of the [Ca2+]i response did not vary, although a decreasing number of cells responded to decreasing PGF2 alpha concentrations (10(-5) to 10(-9) M). PGE2 (10(-4) to 10(-6) M) did not affect [Ca2+]i in rat or human granulosa cells. GnRH (10(-6) M) increased [Ca2+]i in rat but not human granulosa cells. Over 90% of rat granulosa cells tested responded. Angiotensin II (ANG II, 10(-5) M) increased [Ca2+]i in approximately 25% of rat, but not human granulosa cells. Individual rat granulosa cells which responded to GnRH responded to PGF2 alpha and vice versa. Individual rat granulosa cells which responded to ANG II responded to PGF2 alpha and GnRH. Conversely, less than 30% of individual rat granulosa cells which responded to PGF2 alpha and GnRH responded to ANG II. Desensitization (pretreatment) of rat granulosa cells by continuous hormone perifusion suggested that effects of PGF2 alpha, GnRH, and ANG II on [Ca2+]i were receptor specific. However, the effects of combined hormone treatments on [Ca2+]i were not additive. The transient increase in [Ca2+]i in response to PGF2 alpha or GnRH, alone, may be maximal. Results of this study suggested that effects of PGF2 alpha, GnRH, and ANG II receptor-ligand interactions may be at least partially mediated by transient increases in [Ca2+]i in rat granulosa cells. Similarly, effects of PGF2 alpha, but not GnRH or ANG II, receptor-ligand interactions may be mediated by transient increases in [Ca2+]i in human granulosa cells.

Angiotensin II↗
PubMed1992

Inhibition of progestin accumulation by activin-A in human granulosa cells.

The effects of activin and inhibin on steroidogenesis in the human ovary were investigated. Granulosa cells harvested from follicles of women undergoing oocyte recovery for in vitro fertilization were maintained in culture for 4 days before treatment in serum-free medium. Human recombinant inhibin-A and activin-A at concentrations of 100 ng/mL did not affect basal progesterone secretion (P greater than 0.05). Progesterone concentrations were increased 2- to 6-fold by hCG or FSH. Activin-A inhibited the progesterone response to hCG compared with that of cells treated with hCG alone (P less than 0.01). The effect of activin-A was dose dependent and significant at 16-18 h of treatment (P less than 0.01). Inhibin-A at the same concentrations as activin-A had no effect on the progesterone responses to hCG and FSH. The hCG-induced accumulation of 20 alpha-hydroxyprogesterone was also attenuated by simultaneous activin-A treatment compared to that in cells treated with hCG alone (P less than 0.01). To investigate the mechanism of action of activin-A, cells were treated with a cAMP analog (8-bromo-cAMP) or an activator of adenylate cyclase (forskolin), with or without activin-A. Activin-A had no effect on 8-bromo-cAMP-stimulated progesterone accumulation. Likewise, forskolin-stimulated progesterone accumulation was not affected by activin-A. The hCG-induced increase in intracellular cAMP was decreased by activin-A in the presence of a phosphodiesterase inhibitor, isobutylmethylxanthine (P less than 0.01). Thus, activin-A may inhibit progesterone production by suppression of gonadotropin-induced cAMP production. These results support an autocrine role of activin-A in the steroidogenic capacity of human ovarian cells.

Activins↗
PubMed1992

Fast magnetic resonance diffusion-weighted imaging of acute human stroke.

Rapid MRI of the molecular diffusion of water demonstrated cerebral infarcts in 32 patients. We studied these patients at various times following the onset of ischemic symptoms and found that diffusion-weighted imaging revealed the infarcts sooner than conventional T2-weighted spin-echo imaging did; four hyperacute infarcts were shown only by diffusion-weighted imaging. Acute infarcts had lower apparent diffusion coefficients (ADCs) than noninfarcted regions did. This relative difference in ADC reached a nadir in the first 24 hours and rose progressively thereafter. Chronic infarcts showed a relative increase in diffusion and were readily distinguishable from acute infarcts. The technique takes less than 2 minutes to apply using a standard 1.5-tesla scanner in the clinical setting. Diffusion-weighted imaging has the potential to play a role in improving the early anatomic diagnosis of stroke and therefore in the development and implementation of early stroke interventions.

Adult↗
PubMed1992

The status quo, regional differences, and trend of the Chinese family structure.

"Based on the 10% machine aggregate data of the fourth census of 1990 and the 1% computer sampling data, this article attempts to analyze the status quo and regional differences of China's family structure and their relationships with the level of social and economic development, and the trend of the Chinese family structure since the 1980s."

Asia↗
PubMed1992

[Preparation of antigen and antibody against aflatoxin B1].

Carboxymethyloxime of aflatoxin B1 (AFB1) was synthesized by refluxing AF B1 with carboxymethoxylamine hemihydrochloride for 4 hours in the presence of pyridine. AF B1-BSA (antigen) was made successfully by coupling AF B1-oxime with bovine serum albumin (BSA) in the presence of a water soluble carbodiimide. The rabbits were immunized with the artificial immunogen which had been purified by dialysis. The titers of antisera were determined by indirect enzyme-linked immunosorbent assay (ELISA) which was developed by ourselves. The highest titer was 1:100,000.

Aflatoxin B1↗
PubMed1992

An epidemiological survey of deformities and disabilities among 14257 leprosy patients in 11 counties.

This study was planned and conducted in 11 counties in Yangzhou Prefecture, which had formerly had a high prevalence of leprosy. Out of 14257 leprosy patients, 8122 (56.97%) with permanent deformities and disabilities were found. The disability rate was much higher among patients with multibacillary (MB) leprosy (81.15%) than among those with paucibacillary (PB) leprosy (53.04%). The statistical data involving the patients and the types of deformities and disabilities are presented in this paper, and the influences of various host factors and disease factors are discussed.

Adolescent↗
PubMed1992

[Phenotype analysis of mononuclear cells from endomyocardial biopsy specimens in patients with viral myocarditis and dilated cardiomyopathy].

The distribution and phenotype of mononuclear cells from endomyocardial biopsy (EMB) specimens in patients with viral myocarditis (VMC, 25 cases) and dilated cardiomyopathy (DCM, 10 cases) were studied. T-lymphocytes, including T-h/i (T-helper/induced) cells in VMC and T-c/s (T-cytotoxic/suppressor) cells in DCM, were predominated in the infiltrating mononuclear cells within these specimens. The morphological relationship between infiltration of T-lymphocytes and pathological changes of myocardium was also observed, but both macrophages and B-lymphocytes were absent.

Adult↗
PubMed1992

Mitogenic activity for fibroblasts induced by silica and titanium dioxide particles in vitro and in vivo.

Experimental studies on particle-induced pulmonary fibrosis have not provided consistent evidence for the specific induction of fibroblast-regulating cytokines by pulmonary macrophages in response to fibrogenic as compared to non-fibrogenic particles. Using an optimized, wholly serum-free bioassay, we assessed mitogenic activity for pulmonary fibroblasts in supernatants of short-term cultures of alveolar macrophages exposed to either fibrogenic silica or non-fibrogenic titanium dioxide ducts. The responses to these supernatants were influenced by the replicative status of the target cells, in that samples which stimulated non-cycling fibroblasts caused inhibition of DNA synthesis by cycling cells when tested at the same concentration. However, both silica and titanium dioxide elicited comparable secretion of growth factor activity by macrophages, following either in-vitro or in-vivo administration of particles. In contrast, bronchoalveolar lavage fluids from animals that received intratracheal injections of silica, but not from those that received titanium dioxide, exhibited a sustained reduction in fibroblast-stimulating activity. We conclude that secretion of growth factor activity by alveolar macrophages in culture is induced by particles in a non-specific manner. However, alterations in mitogenic activity in bronchoalveolar lavage fluid may constitute a biological marker of the pattern of pulmonary injury which progresses to fibrosis.

Animals↗
PubMed1992

Neuropeptide Y inhibits forskolin-stimulated adenylate cyclase in bovine adrenal chromaffin cells via a pertussis toxin-sensitive process.

The effect of neuropeptide Y (NPY) on adenylate cyclase activity and the role of G-proteins mediating NPY's effect were investigated in cultured bovine adrenal chromaffin cells. The equilibrium binding of [125I]NPY to sucrose gradient purified bovine adrenal medulla plasma membranes revealed high- (GTP gamma S sensitive) and low-affinity binding sites with calculated IC50 values of 0.27 nM and 0.14 microM, respectively. Inhibition of forskolin-stimulated cyclic AMP accumulation was dependent upon the NPY concentration (IC50 = 0.9 nM) and independent of cyclic AMP (cAMP) phosphodiesterase activity. NPY-related peptides, except peptide YY, and NPY fragments exhibited minimal inhibitory activity. The inhibitory effect of NPY on forskolin-stimulated adenylate cyclase activity was completely abolished by pretreatment of the cells with pertussis toxin (PTX). Incubation of membranes with PTX and [32P]nicotinamide adenine dinucleotide revealed a protein band with an apparent molecular mass of 41 kDa. The time course and dose dependence of PTX pretreatment for in vitro ADP-ribosylation were similar to those for PTX to attenuate the NPY effect on forskolin-stimulated adenylate cyclase activity. The direct relation between the NPY receptor and the PTX-sensitive G-protein was further shown by the ability of NPY to inhibit PTX-catalyzed in vitro ADP-ribosylation. ADP-ribosylation of the 41-kDa protein was partially inhibited by 5'-guanylylimidodiphosphate and further inhibited by high concentrations of NPY. An antibody against Gi1/i2 alpha 1 recognized two species of which a 41-kDa protein comigrated with the PTX substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate Ribose↗