Search PubMed⌕ Search

Biomedical subjects

F Gao

Publications and source records attributed to F Gao.

At least 109 records · Page 6Linked to original sources
PubMed2000

Detection of diverse variants of human immunodeficiency virus-1 groups M, N, and O and simian immunodeficiency viruses from chimpanzees by using generic pol and env primer pairs.

Human immunodeficiency virus type 1 (HIV-1) infection of humans is the result of independent cross-species transmissions of simian immunodeficiency viruses (SIVcpz) from naturally infected chimpanzees (Pan troglodytes troglodytes) to man. To develop a polymerase chain reaction-based assay capable of detecting members of all major phylogenetic SIVcpz and HIV-1 lineages (groups M, N, and O), primer pairs in conserved pol and env regions were designed. Both primer sets amplified </=10 copies of selected group M reference clones (subtypes A-H), proviral DNA or RNA of group N (YBF30), and group O of HIV-1 and also amplified divergent SIVcpz from cultured isolates (SIVcpzGAB1 and SIVcpzANT), uncultured spleen tissue (SIVcpzUS), and plasma (SIVcpzANT and SIVcpzUS). Sequences of the 2 amplicons (445 bp for gp41 and 261 bp for integrase) are of sufficient length for phylogenetic analyses, allowing both group and subtype classifications of the human viruses. Finally, both primer pairs are highly sensitive (>99%) in amplifying viral sequences from plasma taken from patients infected with HIV-1 group M (n=226) and O (n=17) viruses.

Animals↗
PubMed2000

Precambrian animal diversity: putative phosphatized embryos from the Doushantuo Formation of China.

Putative fossil embryos and larvae from the Precambrian phosphorite rocks of the Doushantuo Formation in Southwest China have been examined in thin section by bright field and polarized light microscopy. Although we cannot completely exclude a nonbiological or nonmetazoan origin, we identified what appear to be modern cnidarian developmental stages, including both anthozoan planula larvae and hydrozoan embryos. Most importantly, the sections contain a variety of small (</=200 microm) structures that greatly resemble gastrula stage embryos of modern bilaterian forms.

Animals↗
PubMed2000

Mechanically gated channel activity in cytoskeleton-deficient plasma membrane blebs and vesicles from Xenopus oocytes.

1. A novel technique involving hypertonic stress causes membrane 'blebbing' of the Xenopus oocyte and the shedding of plasma membrane vesicles (PMVs). 2. Confocal fluorescence microscopy, immunocytochemistry and electron microscopy indicate that blebs and PMVs lack cortical cytoskeleton and are deficient in cytoskeleton proteins and devoid of microvilli. 3. Patch recordings from PMVs consistently reveal mechanically gated (MG) channel activity. The MG channels display the same single-channel conductance as control recordings but differ in terms of reduced mechanosensitivity and adaptation to sustained stimulation. 4. Whole PMV recordings show rapid and reversible activation of mechanosensitive currents in response to pressure pulses. The maximal currents activated in PMVs are consistent with MG channel activity recorded in patches. 5. The discrepancy between MG channel activity recorded in whole PMVs and oocytes most probably reflects their different membrane geometry and ability to develop activating bilayer tensions. 6. We propose that membrane blebbing, which is known to occur under specific physiological and pathological conditions (e.g. mitosis and apoptosis), may increase mechanosensitivity independently of the intrinsic properties of membrane proteins.

Animals↗
PubMed2000

Alpha2 macroglobulin and the risk of Alzheimer's disease.

BACKGROUND: alpha2 Macroglobulin is a panproteinase inhibitor that is found immunohistochemically in neuritic plaques, a requisite neuropathologic feature of AD. Recently, a pentanucleotide deletion near the 5' end of the "bait region" of the alpha2 macroglobulin (A2M) gene was reported to be associated with AD in a large cohort of sibpairs, in which the mutation conferred a similar odds ratio with AD as the APOE-epsilon4 allele for carriers of at least one copy of the A2M gene (Mantel-Haenszel odds ratio, 3.56). METHODS: We studied three independent association samples of AD patients (n = 309) with an age range of 50 to 94 years and representative controls (n = 281) to characterize the allele frequency of the pentanucleotide deletion in this cohort. We detected the mutation near the 5' splice site of exon 18 using standard PCR and restriction fragment length polymorphism methods. The results were adjusted for age, gender, education, and APOE polymorphism. RESULTS: We found that the A2M gene polymorphism conferred an increased risk for AD, with an estimated Mantel-Haenszel ratio of 1.5 (95% CI 1.1 to 2.2; p = 0.025). There was no age- or gender-dependent increase in A2M gene allele frequencies in AD patients compared with controls. The combined sample showed the expected association between AD and APOE-epsilon 4. In one of our three samples there was an interaction between the A2M and APOE-epsilon4 genes, but the other two samples showed no interaction between the two risk factors. CONCLUSIONS: Our data support an association between the A2M gene and AD. This association is less pronounced, however, in our cohort than in the previously reported sample of sibpairs.

Aged↗
PubMed2000

What do infants know about continuous quantity?

We investigated infants' sensitivity to amount of continuous quantity and to change in amount of continuous quantity. Using a habituation procedure, Experiment 1 examined whether 6-month-old infants can distinguish between different amounts of liquid in a container. Infants looked significantly longer at a novel quantity than at the familiar quantity. Using a violation-of-expectation paradigm, Experiment 2 examined whether 9-month-old infants expect a change in amount when liquid is added to a hidden container which is already one-fourth full of liquid. Infants looked significantly longer at the impossible event than at the possible event. These findings indicate that infants are sensitive to amount, calling into question claims that infants have a quantitative mechanism which is exclusive to number.

Cognition↗
PubMed2000

Remote spatial memory in an amnesic person with extensive bilateral hippocampal lesions.

The hippocampus may have a time-limited role in memory, being needed only until information is permanently stored elsewhere, or this region may permanently represent long-term allocentric spatial information or cognitive maps in memory. To test these ideas, we investigated remote spatial memory in K.C., a patient with bilateral hippocampal lesions and amnesia for autobiographical events. In his spatial knowledge, general aspects were preserved, but details were lost, a pattern that resembled his memory loss in other domains. K.C. performed normally on allocentric spatial tests of his neighborhood and the world. He had difficulty, however, in recognizing and identifying non-salient neighborhood landmarks, and in recognizing city locations on world maps. This suggests that the hippocampus is not crucial for maintenance and retrieval of remotely formed spatial representations of major landmarks, routes, distances and directions, but is necessary for specifying location details, regardless of when they were acquired.

Amnesia↗
PubMed2000

Origins and evolution of AIDS viruses: estimating the time-scale.

The primate lentiviruses comprise SIV strains from various host species, as well as two viruses, HIV-1 and HIV-2, that cause AIDS in humans. The origins of HIV-1 and HIV-2 have been traced to cross-species transmissions from chimpanzees and sooty mangabey monkeys respectively. Two approaches have been taken to estimate the time-scale of the evolution of these viruses. Certain groups of SIV strains appear to have evolved in a host-dependent manner, implying a time-scale of many thousands or even millions of years. In stark contrast, molecular clock calculations have previously been used to estimate a time-scale of only tens or hundreds of years. Those calculations largely ignored heterogeneity of evolutionary rates across different sites within sequences. In fact, the distribution of rates at different sites seems extremely skewed in HIV-1, and so the time-depth of the primate lentivirus evolutionary tree may have been underestimated by at least a factor of ten. However, these date estimates still seem to be far too recent to be consistent with host-dependent evolution.

Animals↗
PubMed2000

Nerve tissue protein S-100 and neurone-specific enolase concentrations in cerebrospinal fluid and blood during carotid endarterectomy.

Nerve tissue protein S-100 and neurone-specific enolase levels in serum were studied in 10 patients before, during and for 2 days after elective carotid endarterectomy performed under general anaesthesia and using a Javid Shunt. In six patients, simultaneous cerebrospinal fluid samples were also obtained. Serum nerve tissue protein S-100 was normal throughout the operation, but in one patient with severe hypertension, levels increased to 1.38 microg. l-1 at 1 h postoperatively. Two patients showed an increase in cerebrospinal fluid nerve tissue protein S-100 during clamping: these patients also had neurological deficits at 6 months. Serum neurone-specific enolase increased from 5.8 to 9.3 microg.l-1 during shunting while cerebrospinal fluid neurone-specific enolase did not change. Uncomplicated carotid endarterectomy does not produce cerebral damage as measured by serum nerve tissue protein S-100; cerebrospinal fluid nerve tissue protein S-100 may be more sensitive for minor cerebral damage. Neurone-specific enolase appeared to be nonspecific. The lack of correlation between the neuroproteins may need to be explained before relying on these simple assays as diagnostic indicators of cerebral ischaemia.

Aged↗
PubMed2000

Mammographic parenchymal patterns and risk of breast cancer at and after a prevalence screen in Singaporean women.

BACKGROUND: The objective of this study was to assess the effect of mammographic parenchymal patterns on risk of breast cancer detected at first screen or in the period following a negative screen. METHODS: The study utilizes a nested case-control design with 132 breast cancer patients detected at first screen (from a total of 29 193 screened) and 42 breast cancer patients detected in the period following the first screen. These patients were matched to 348 screened-negative controls. The mammograms were classified according to Tabar's classification for parenchymal pattern and statistical analysis was done by conditional logistic regression. RESULTS: The risk of breast cancer for women with Tabar pattern IV was significantly high when compared to the remaining patterns (odds ratio 2.59). Risk factors for Tabar pattern IV coincided largely with established risk factors for breast cancer. CONCLUSION: The study confirms the increased risk of breast cancer associated with Tabar pattern IV (approximately Wolfe pattern P2), in an Asian population. This pattern is associated with nulliparity and high educational status and is strongly associated with grade 3 cancers.

Asian People↗
PubMed2000

Mechanism of decreased adenosine protection in reperfusion injury of aging rats.

The purpose of this study was to determine whether the protective effects of adenosine on myocardial ischemia-reperfusion injury are altered with age, and if so, to clarify the mechanisms that underlie this change related to nitric oxide (NO) derived from the vascular endothelium. Isolated perfused rat hearts were exposed to 30 min of ischemia and 60 min of reperfusion. In the adult hearts, administration of adenosine (5 micromol/l) stimulated NO release (1. 06 +/- 0.19 nmol. min(-1). g(-1), P < 0.01 vs. vehicle), increased coronary flow, improved cardiac functional recovery (left ventricular developed pressure 79 +/- 3.8 vs. 57 +/- 3.1 mmHg in vehicle, P < 0.001; maximal rate of left ventricular pressure development 2,385 +/- 103 vs. 1,780 +/- 96 in vehicle, P < 0.001), and reduced myocardial creatine kinase loss (95 +/- 3.9 vs. 159 +/- 4.6 U/100 mg protein, P < 0.01). In aged hearts, adenosine-stimulated NO release was markedly reduced (+0.42 +/- 0.12 nmol. min(-1). g(-1) vs. vehicle), and the cardioprotective effects of adenosine were also attenuated. Inhibition of NO production in the adult hearts significantly decreased the cardioprotective effects of adenosine, whereas supplementation of NO in the aged hearts significantly enhanced the cardioprotective effects of adenosine. The results show that the protective effects of adenosine on myocardial ischemia-reperfusion injury are markedly diminished in aged animals, and that the loss in NO release in response to adenosine may be at least partially responsible for this age-related alteration.

Adenosine↗
PubMed2000

I4AA-Sensitive chloride current contributes to the center light responses of bipolar cells in the tiger salamander retina.

Light-evoked currents in depolarizing and hyperpolarizing bipolar cells (DBCs and HBCs) were recorded under voltage-clamp conditions in living retinal slices of the larval tiger salamander. Responses to illumination at the center of the DBCs' and HBCs' receptive fields were mediated by two postsynaptic currents: DeltaI(C), a glutamate-gated cation current with a reversal potential near 0 mV, and DeltaI(Cl), a chloride current with a reversal potential near -60 mV. In DBCs DeltaI(C) was suppressed by L-2-amino-4-phosphonobutyric acid (L-AP4), and in HBCs it was suppressed by 6,7-dinitroquinoxaline-2,3-dione (DNQX). In both DBCs and HBCs DeltaI(Cl) was suppressed by imidazole-4-acetic acid (I4AA), a GABA receptor agonist and GABA(C) receptor antagonist. In all DBCs and HBCs examined, 10 microM I4AA eliminated DeltaI(Cl) and the light-evoked current became predominately mediated by DeltaI(C). The addition of 20 microM L-AP4 to the DBCs or 50 microM DNQX to HBCs completely abolished DeltaI(C). Focal application of glutamate at the inner plexiform layer elicited chloride currents in bipolar cells by depolarizing amacrine cells that release GABA at synapses on bipolar cell axon terminals, and such glutamate-induced chloride currents in DBCs and HBCs could be reversibly blocked by 10 microM I4AA. These experiments suggest that the light-evoked, I4AA-sensitive chloride currents (DeltaI(Cl)) in DBCs and HBCs are mediated by narrow field GABAergic amacrine cells that activate GABA(C) receptors on bipolar cell axon terminals. Picrotoxin (200 microM) or (1,2,5,6-tetrahydropyridine-4yl) methyphosphinic acid (TPMPA) (2 other GABA(C) receptor antagonists) did not block (but enhanced and broadened) the light-evoked DeltaI(Cl), although they decreased the chloride current induced by puff application of GABA or glutamate. The light response of narrow field amacrine cells were not affected by I4AA, but were substantially enhanced and broadened by picrotoxin. These results suggest that there are at least two types of GABA(C) receptors in bipolar cells: one exhibits stronger I4AA sensitivity than the other, but both can be partially blocked by picrotoxin. The GABA receptors in narrow field amacrine cells are I4AA insensitive and picrotoxin sensitive. The light-evoked DeltaI(Cl) in bipolar cells are mediated by the more strongly I4AA-sensitive GABA(C) receptors. Picrotoxin, although acting as a partial GABA(C) receptor antagonist in bipolar cells, does not suppress DeltaI(Cl) because its presynaptic effects on amacrine cell light responses override its antagonistic postsynaptic actions.

Ambystoma↗
PubMed2000

Role of the amino acid 45 residue in reduced folate carrier function and ion-dependent transport as characterized by site-directed mutagenesis.

In previous reports, an E45K mutation in reduced folate carrier (RFC1) resulted in marked substrate-specific changes in folate binding and the induction of an obligatory inorganic anion requirement for carrier function. In this study, site-directed mutagenesis was employed to further characterize the role of glutamate-45 in carrier function by replacement with glutamine, arginine, aspartate, leucine, or tryptophan followed by tranfection of the mutated cDNAs into the MTX(r)A line, which lacks a functional endogenous carrier. Alterations in transport function with amino acid substitutions at this residue were not charge related. Hence, E45Q, E45R, and E45K all 1) increased carrier affinity for 5-formyltetrahydrofolate approximately 4-fold, 2) increased affinity for folic acid approximately 6- to 10-fold, 3) did not change affinity for 5-methyltetrahydrofolate, and 4) except for E45R decreased affinity for methotrexate (2- to 3-fold). In contrast, mutations E45D, E45L, and E45W generally reduced affinity for all these folates except for folic acid. Finally, chloride-dependent influx was only noted in the E45R mutant. These data further substantiate the important role that glutamate-45 plays in the selectivity of binding of folates to RFC1 and establish that it is the addition of a positive charge at this site and not the loss of a negative charge that results in the induced anion dependence. These and other studies indicate that mutations in the first transmembrane domain can have a markedly selective impact on the affinity of RFC1 for folate compounds and in particularly a highly salutary effect on binding of the oxidized folate, folic acid.

Amino Acid Substitution↗
PubMed2000

Peroxynitrite, a two-edged sword in post-ischemic myocardial injury-dichotomy of action in crystalloid- versus blood-perfused hearts.

Peroxynitrite (ONOO(-)) is widely recognized as a mediator of NO. toxicity, but recent studies have indicated that this compound may also have physiologic activity and induces vascular relaxation as well as inhibition of platelet aggregation and neutrophil adhesion. The present experiment was designed to determine whether ONOO(-) may exert different effects on postischemic myocardial injury in a crystalloid perfusion environment versus a blood perfusion environment and, if it does, to clarify the mechanisms causing any differences. In Krebs-Henseleit buffer-perfused rabbit hearts, administration of ONOO(-) at the onset of reperfusion enhanced myocardial injury in a concentration-dependent fashion with a significant effective concentration of 30 microM. In contrast, in blood-perfused hearts, administration of ONOO(-) (1 to 30 microM) significantly attenuated postmyocardial injury as evidenced by improved cardiac function recovery, preserved endothelial function, decreased myocardial creatine kinase loss, and reduced necrotic size. The minimal and maximal protective concentrations were determined to be 1 and 3 microM, respectively. When a high concentration of ONOO(-) (i.e., 100 microM) was administered, a detrimental effect was observed. Administration of ONOO(-) decreased neutrophil accumulation in the ischemic-reperfused myocardial tissue in a concentration-dependent manner in blood-perfused hearts and inhibited neutrophil adhesion to cultured endothelial cells exposed to hypoxia/reoxygenation. Taken together, these results demonstrate that ONOO(-) may act as a "double-edged sword" in postischemic myocardial injury. This compound is directly toxic to the cardiac tissue at a relatively high concentration, but it can indirectly protect myocardial cells from neutrophil-induced injury at a much lower concentration.

Animals↗
PubMed2000

Effects of betaxolol on light responses and membrane conductance in retinal ganglion cells.

PURPOSE: To examine the physiological effects of betaxolol, a beta1-adrenergic receptor blocker commonly used in the treatment of glaucoma, on retinal ganglion cells and to evaluate its potential to elicit responses consistent with a neuroprotective agent against ganglion cell degeneration. METHODS: Single-unit extracellular recording, electroretinogram (ERG), intracellular and whole-cell patch-clamp recording techniques were made from flatmounted, isolated retina, superfused eyecup, and living retinal slice preparations of the larval tiger salamander. RESULTS: Bath application of 20 microM betaxolol reduced the glutamate-induced increase of spontaneous spike rate in retinal ganglion cell by approximately 30%. The glutamate-induced postsynaptic current recorded under voltage-clamp conditions was reduced by 50 microM betaxolol, and the difference current-voltage (I-V) relation (I(Control)-I(betaxolol)) was N-shaped and AP5-sensitive, characteristic of N-methyl-D-aspartate receptor-mediated current. Application of 50 microM betaxolol reversibly reduced the voltage-gated sodium and calcium currents by approximately one third of their peak amplitudes. The times-to-action of betaxolol on ganglion cells are long (15-35 minutes for 20-50 microM betaxolol), indicative of modulation through slow biochemical cascades. Betaxolol, up to 100 microM, exerted no effects on horizontal cells or the ERG, suggesting that the primary actions of this beta1 blocker are restricted to retinal ganglion cells. CONCLUSIONS: These physiological experiments provide supporting evidence that betaxolol acts in a manner consistent with preventing retinal ganglion cell death induced by elevated extracellular glutamate or by increased spontaneous spike rates under pathologic conditions. The physiological actions of betaxolol lead to reducing neurotoxic effects in ganglion cells, which are the most susceptible retinal neurons to glutamate-induced damages under ischemic and glaucomatous conditions. Therefore, betaxolol has the potential to be a neuroprotective agent against retinal degeneration in patients with disorders mediated by such mechanisms.

Adrenergic beta-Antagonists↗
PubMed2000

Sensitivity to 5,10-dideazatetrahydrofolate is fully conserved in a murine leukemia cell line highly resistant to methotrexate due to impaired transport mediated by the reduced folate carrier.

A murine leukemia cell line was identified that is highly resistant to methotrexate (MTX), due to impaired transport, but fully sensitive to 5,10-dideazatetrahydrofolate (DDATHF). A valine-to-methionine substitution at amino acid 104 in the reduced folate carrier (RFC1) explains this disparity in drug resistance. Transfection of the V104M cDNA into an RFC1-deficient cell line markedly increased DDATHF influx (32x) but only modestly increased influx of MTX and 5-formyltetrahydrofolate (4- and 6-fold, respectively). The growth inhibition or growth requirements for these folates fell by factors of 18, 2, and 4, respectively, in the transfectant. Preservation of DDATHF influx in cells with V104M RFC1 resulted in even greater preservation (60%) of the exchangeable drug level. Another major element in the preservation of DDATHF activity was the impact of the mutated carrier on cellular folate pools. For folic acid, folate pools were essentially unchanged but DDATHF polyglutamate levels decreased in lines that express the V104M carrier. However, with 5-formyltetrahydrofolate as the growth source, there was a marked decrease in folate pools in the lines carrying the mutated carrier, and DDATHF polyglutamate levels were unchanged. Hence, DDATHF activity was preserved in cells with V104M RFC1 due to (a) relative conservation of DDATHF transport, and (b) depletion of cellular THF cofactors with diminishing folate cofactor competition at folylpolyglutamate synthetase and possibly glycinamide ribonucleotide formyltransferase. Hence, resistance to one antifolate, in this case MTX, because of a loss of RFC1 transport activity need not exclude the subsequent utility of another antifolate that uses the same carrier.

Amino Acids↗
PubMed2000

The mechanism of transport of the multitargeted antifolate (MTA) and its cross-resistance pattern in cells with markedly impaired transport of methotrexate.

MTA (LY231514) is an antifolate that targets multiple folate-dependent enzymes. In this report, MTA transport was characterized in wild-type L1210 cells and variants with impaired membrane transport or polyglutamation. MTA influx via the reduced folate carrier was somewhat faster (approximately 30%) than that for methotrexate (MTX). Unlike MTX, MTA was rapidly polyglutamated in L1210 cells; hence, a folylpoly-gamma-glutamate synthetase-deficient L1210 variant was used to assess net transport and efflux properties. The MTA transmembrane gradient for exchangeable drug was 2.5 times greater than the MTX gradient, attributable primarily to an efflux rate constant 40% that of MTX. No MTA was bound to dihydrofolate reductase. When grown with folic acid, MTX-resistant L1210 variants with mutations in the reduced folate carrier demonstrated cross-resistance to MTA, markedly reduced MTA accumulation, and only a slightly decreased intracellular folate cofactor pool as compared to L1210 cells. However, when 5-formyltetrahydrofolate was the growth substrate, these MTX-resistant cells were less resistant or negligibly resistant to MTA, accumulated more MTA, and had a lower folate pool as compared to L1210 cells. MTA activity and the intracellular folate pool in L1210 cells were inversely related. These data indicate that MTA polyglutamation in L1210 cells is favored by both the generation of high intracellular drug levels and high MTA affinity for FPGS relative to MTX. Cells resistant to MTX because of impaired transport may retain appreciable sensitivity to MTA because of a concurrent reduction in tetrahydrofolate cofactor transport resulting in cellular folate depletion, which diminishes endogenous folate suppression of MTA polyglutamation.

Animals↗