PubMed Health⌕ Search

Biomedical subjects

B Tian

Publications and source records attributed to B Tian.

At least 19 recordsLinked to original sources
PubMed2000

Chronopotentiometric analysis of highly resistive media

Reciprocal derivative chronopotentiometry is shown to be well suited for performing electrochemistry in highly resistive solutions in connection to conventional-sized electrodes. The fundamentally different operational principles of reciprocal derivative chronopotentiometry (compared to controlled-potential voltammetry) reduces its susceptibility to solution resistance effects. The influences of the electrolyte concentration and constant current upon the reciprocal derivative chronopotentiometric peak area and potential are examined in different solvents. Well-defined, analytically useful peaks are observed in highly resistive media (with low electrolyte/analyte ratios). Narrower peaks, shifted to higher potential values, are observed upon increasing the solution resistance. Yet, the analytical signal (square root of the peak area) is nearly independent of the ohmic drop. The experimental results are compared with the theoretical predictions. Considerable ohmic drop distortions are observed in analogous voltammetric experiments. The defined chronopotentiometric peaks permit convenient quantitation of micromolar analyte concentrations in highly resistive media. Such observations open the door to new electrochemical applications of conventional electrodes that were previously restricted to ultramicroelectrodes.

Journal Article↗
PubMed2000

Lab-on-a-Cable for electrochemical monitoring of phenolic contaminants.

The "Lab-on-a-Cable" concept, based on scaling down an electrochemical flow system to a cable platform, is described. The system integrates the analyte collection and the sample handling, with the electrochemical detection of the reaction product in a sealed cylindrical unit, connected to a long shielded cable. An enzymatic assay, involving collection of a phenolic substrate, its mixing with an internally delivered tyrosinase solution, and amperometric detection of the liberated quinone product, is used for illustrating the operation of the flow probe and demonstrating its advantages over remote phenol sensors. The internal buffer solution ensures independence of sample conditions such as pH, ionic strength, or natural conditions, that commonly influences the performance of remote sensors. The "built-in" flow pulsation of the integrated micropump is exploited for a sensitive hydrodynamic-modulation voltammetric detection of hydrazine and peroxide pollutants.

Electrochemistry↗
PubMed2000

Microfabricated electrophoresis chips for simultaneous bioassays of glucose, uric acid, ascorbic acid, and acetaminophen.

A micromachined capillary electrophoresis chip is described for simultaneous measurements of glucose, ascorbic acid, acetaminophen, and uric acid. Fluid control is used to mix the sample and enzyme glucose oxidase (GOx). The enzymatic reaction, a catalyzed aerobic oxidation of glucose to gluconic acid and hydrogen peroxide, occurs along the separation channel. The enzymatically liberated neutral peroxide species is separated electrophoretically from the anionic uric and ascorbic acids in the separation/reaction channel. The three oxidizable species are detected at the downstream gold-coated thick-film amperometric detector at different migration times. Glucose can be detected within less than 100 s, and detection of all electroactive constituents is carried out within 4 min. Measurements of glucose in the presence of acetaminophen, a neutral compound, are accomplished by comparing the responses in the presence and absence of GOx in the running buffer. The reproducibility of the on-chip glucose measurements is improved greatly by using uric acid as an internal standard. Factors influencing the performance, including the GOx concentration, field strength, and detection potential, are optimized. Such coupling of enzymatic assays with electrophoretic separations on a microchip platform holds great promise for rapid testing of metabolites (such as glucose or lactate), as well as for the introduction of high-speed clinical microanalyzers based on multichannel chips.

Acetaminophen↗
PubMed2000

Functional role of cyclin A on induction of fibroblast apoptosis due to ligation of CD44 matrix receptor by anti-CD44 antibody.

Ligation of cell surface matrix adhesion receptors such as integrins can increase expression of specific cell cycle regulatory proteins such as cyclin A, thereby regulating cell cycle progression. Disruption of cell surface matrix receptor interaction with the extracellular matrix can trigger apoptosis. Induction of apoptosis has been linked to unscheduled up-regulation of cyclin A and activation of cyclin-A-associated dependent kinase 2 activity due to cleavage of cyclin-dependent kinase inhibitors by caspases. We have found that ligation of the cell surface matrix adhesion receptor CD44 by anti-CD44 antibody induces cell detachment and triggers apoptosis. In this report we show that ligation of CD44 by anti-CD44 antibody increases the expression of cyclin A protein prior to activation of caspase-3-like activity and morphological changes of apoptosis. Down-regulation of cyclin A protein levels by cyclin A antisense oligonucleotides dramatically decreased fibroblast apoptosis in response to anti-CD44 antibody. These data identify an important functional role of cyclin A in the induction of fibroblast apoptosis due to the ligation of the cell surface adhesion receptor CD44 by anti-CD44 antibody.

3T3 Cells↗
PubMed2000

A positron emission tomographic study of auditory localization in the congenitally blind.

We have used positron emission tomography (PET) to measure regional cerebral blood flow (rCBF) in sighted and congenitally blind subjects performing auditory localization tasks. During scanning, the spectral and binaural cues of localized sound were reproduced by a sound system and delivered via headphones. During tasks that required auditory localization both the sighted and blind subjects strongly activated posterior parietal areas. In addition, the blind subjects activated association areas in the right occipital cortex, the foci of which were similar to areas previously identified in visual location and motion detection experiments in sighted subjects. The blind subjects, therefore, demonstrated visual to auditory cross-modal plasticity with auditory localization activating occipital association areas originally intended for dorsal-stream visual processing. To determine the functional connectivity of pre-selected brain regions in primary and non-primary auditory and posterior parietal cortex in the two cohorts, we performed an inter-regional correlation analysis on the rCBF data set. During auditory localization in the blind subjects, rCBF activity in the right posterior parietal cortex was positively correlated with that in the right occipital region, whereas in sighted subjects correlations were generally negative. There were no significant positive occipital correlations in either cohort when reference regions in temporal or left parietal cortex were chosen. This indicates that in congenitally blind subjects the right occipital cortex participates in a functional network for auditory localization and that occipital activity is more likely to arise from connections with posterior parietal cortex.

Adult↗
PubMed2000

Effect of latrunculin-B on outflow facility in monkeys.

Latrunculin-B (LAT-B), a macrolide derived from the marine sponge Latrunculia magnifica, sequesters monomeric G-actin, leading to the disassembly of actin filaments in cultured cells. In this study, we determined the effect of LAT-B on outflow facility in living monkeys. Total outflow facility was measured by 2-level constant pressure perfusion of the anterior chamber (AC) before and immediately after AC exchange infusion or 2 hr after topical application of LAT-B or vehicle. Both AC exchange infusion and topical application of LAT-B dose- and time-dependently increased outflow facility by two- to four-fold. Those findings suggest that pharmacological disorganization of the actin cytoskeleton in the trabecular meshwork by specific actin inhibitors such as LAT-B may be a useful anti-glaucoma strategy.

Animals↗
PubMed2000

Expanded CUG repeat RNAs form hairpins that activate the double-stranded RNA-dependent protein kinase PKR.

Myotonic dystrophy is caused by an expanded CTG repeat in the 3' untranslated region of the DM protein kinase (DMPK) gene. The expanded repeat triggers the nuclear retention of mutant DMPK transcripts, but the resulting underexpression of DMPK probably does not fully account for the severe phenotype. One proposed disease mechanism is that nuclear accumulation of expanded CUG repeats may interfere with nuclear function. Here we show by thermal melting and nuclease digestion studies that CUG repeats form highly stable hairpins. Furthermore, CUG repeats bind to the dsRNA-binding domain of PKR, the dsRNA-activated protein kinase. The threshold for binding to PKR is approximately 15 CUG repeats, and the affinity increases with longer repeat lengths. Finally, CUG repeats that are pathologically expanded can activate PKR in vitro. These results raise the possibility that the disease mechanism could be, in part, a gain of function by mutant DMPK transcripts that involves sequestration or activation of dsRNA binding proteins.

Base Pairing↗
PubMed2000

Renal interstitial Ca(2+).

Renal interstitial fluid Ca(2+) concentration ([Ca(2+)](isf)) was measured in anesthetized Wistar rats by using in situ microdialysis. During perfusion of 20 cm of the proximal small intestine with Ca(2+)-free buffer, renal [Ca(2+)](isf) was 1.63 +/- 0.19 mmol/l in the cortex (n = 6) and 1.93 +/- 0.12 mmol/l in the medulla (n = 5, P = 0.223). When Ca(2+) in the intestinal lumen was increased to 3 mmol/l, no change was seen in total or ionized serum Ca(2+) (S(Ca)), urinary Ca(2+) excretion (U(Ca)), or Ca(2+) in a microdialysate of the kidney cortex. Increasing intestinal Ca(2+) further, to 6 mmol/l, was without effect on S(Ca) but significantly increased U(Ca) by 38% and microdialysate Ca(2+) by 36% (1.25 +/- 0.0.09 vs. 1.70 +/- 0. 14 mmol/l, n = 4, P < 0.05). Intravenous infusion of 28 ng. kg(-1). min(-1) of parathyroid hormone for 1 h during perfusion of the intestinal lumen with 1 mmol/ Ca(2+)caused a 7-10% rise in S(Ca), a 40% fall in U(Ca), and a 32% increase in microdialysate Ca(2+) (1.32 +/- 0.13 vs. 1.74 +/- 0.13 mmol/l, n = 6, P < 0.05). Interlobar arteries with a mean diameter of 120 microm were studied by using a wire myograph to determine whether changes in extracellular Ca(2+) affect muscle tone. When precontracted with 5 micromol/l serotonin, the arteries relaxed in response to cumulative addition of Ca(2+) (1-5 mmol/l) with an ED(50) value for Ca(2+) of 3.30 +/- 0.08 mmol/l, n = 3. These data demonstrate that [Ca(2+)](isf) changes dynamically during manipulation of whole-animal Ca(2+) homeostasis and that intrarenal arteries relax in response to extracellular Ca(2+) varied over the range measured in vivo.

Animals↗
PubMed2000

Latrunculins' effects on intraocular pressure, aqueous humor flow, and corneal endothelium.

PURPOSE: To determine the effects of latrunculin (LAT)-A or -B on intraocular pressure (IOP), aqueous humor flow (AHF), anterior chamber (AC) protein concentration ([protein]AC), corneal endothelial permeability and morphology, and corneal thickness in living cynomolgus monkeys. METHODS: Topical LAT-A or LAT-B was administered to one eye, and vehicle to the other. IOP was measured by Goldmann tonometry, AHF and corneal endothelium transfer coefficient (ka) by fluorophotometry, [protein]Ac by Lowry assay, corneal endothelial cell morphology by specular microphotography, and corneal thickness by ultrasound pachymetry. RESULTS: LAT-A began to lower IOP at 6 hours and maximally reduced IOP by 4.6 mm Hg at 9 hours. LAT-B lowered IOP within 1 hour and maximally reduced IOP by 3.1 mm Hg at 6 hours. LAT-A increased AHF by 87% for 3 hours and increased ka by 94% over 6 hours; LAT-B increased ka by 39% over 6 hours without affecting AHF. LAT-A increased IV fluorescein entry into the cornea approximately 10 fold, but did not affect IV fluorescein entry into the AC. LAT-A increased [protein]AC by 25% at 2 hours but not 5.5 hours. LAT-B variably and insignificantly increased [protein]AC: at 1 hour but not at 6.5 hours. LAT-A induced extensive corneal endothelial pseudoguttata within 1 hour, with normal cell counts by 7 days. LAT-B increased central corneal thickness maximally by 47 microm at 3.5 hours. CONCLUSIONS: LAT-A and -B significantly reduced IOP and were consistent in their facility-increasing effect, indicating that pharmacologic disorganization of the actin cytoskeleton in the trabecular meshwork by latrunculins may be a useful antiglaucoma strategy. However, effects on corneal endothelium or ciliary epithelium are a potential safety issue.

Animals↗
PubMed2000

H-7 effects on the structure and fluid conductance of monkey trabecular meshwork.

OBJECTIVE: To determine the effects of H-7 (1-[5-isoquinoline sulfonyl]-2-methyl piperazine) on the structure and fluid conductance of the trabecular meshwork of live cynomolgus monkeys. METHODS: Fluid outflow was measured by constant pressure perfusion of the anterior chamber with cationized and noncationized gold solution with or without H-7 in opposite eyes. The eyes were fixed by infusing Ito solution and enucleated. Anterior segments were cut into 4 sections, fixed in immersion solution, and embedded in epoxy resin-812. Trabecular meshwork morphologic features were studied by light and electron microscopy. RESULTS: H-7 affected trabecular meshwork organization and increased fluid outflow. H-7 expanded the intercellular spaces in the juxtacanalicular meshwork, accompanied by removal of extracellular material. The inner wall cells of the Schlemm canal became highly extended, yet cell-cell junctions were maintained. Colloidal gold particles were detected only in limited areas along the subcanalicular region in control eyes; after H-7 treatment, gold was widely seen along the entire inner canal wall. Most inner wall cells in H-7-treated eyes, but only few cells in control eyes, contained gold-loaded vesicles. CONCLUSION: H-7 inhibits cell contractility, leading to "relaxation" of the trabecular outflow pathway, expanding the draining surface, and permitting more extensive flow through the meshwork. CLINICAL RELEVANCE: By inhibiting cellular contractility and relaxing the trabecular meshwork, the protein kinase inhibitor H-7 increases outflow facility and reduces intraocular pressure and thus has potential as an ocular hypotensive antiglaucoma medication. Arch Ophthalmol. 2000;118:955-962

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1999

A PET study of human auditory spatial processing.

To learn more about human auditory spatial processing, we used positron emission tomography (PET) to measure regional cerebral blood flow in human volunteers engaged in sound localization tasks. Spectral and binaural cues of localized sound were reproduced by a sound system and delivered via headphones. During localization tasks, subjects activated inferior parietal lobules (IPL) bilaterally. In a second experiment, matched in design to the first, subjects made non-spatial auditory discriminations based on frequency, activating the IPL bilaterally with left hemispheric predominance. A between-study comparison revealed that the right IPL was significantly more activated during the sound localization task compared with the feature discrimination task, suggesting a preferential role for the right IPL in auditory spatial processing.

Adult↗
PubMed1999

Tumor necrosis factor alpha stimulates lipolysis in adipocytes by decreasing Gi protein concentrations.

Prolonged treatment (12-24 h) of adipocytes with tumor necrosis factor alpha (TNFalpha) stimulates lipolysis. We have investigated the hypothesis that TNFalpha stimulates lipolysis by blocking the action of endogenous adenosine. Adipocytes were incubated for 48 h with TNFalpha, and lipolysis was measured in the absence or presence of adenosine deaminase. Without adenosine deaminase, the rate of glycerol release was 2-3-fold higher in the TNFalpha-treated cells, but with adenosine deaminase lipolysis increased in the controls to approximately that in the TNFalpha-treated cells. This suggests that TNFalpha blocks adenosine release or prevents its antilipolytic effect. Both N6-phenylisopropyl adenosine and nicotinic acid were less potent and efficacious inhibitors of lipolysis in treated cells. A decrease in the concentration of alpha-subunits of all three Gi subtypes was detected by Western blotting without a change in Gs proteins or beta-subunits. Gi2alpha was about 50% of control, whereas Gi1alpha and Gi3alpha were about 20 and 40% of control values, respectively. The time course of Gi down-regulation correlated with the stimulation of lipolysis. Furthermore, down-regulation of Gi by an alternative approach (prolonged incubation with N6-phenylisopropyl adenosine) stimulated lipolysis. These findings indicate that TNFalpha stimulates lipolysis by blunting endogenous inhibition of lipolysis. The mechanism appears to be a Gi protein down-regulation.

Adipocytes↗
PubMed1999

Combined effects of H-7 and cytochalasin B on outflow facility in monkeys.

The serine-threonine protein kinase inhibitor H-7 and the fungal metabolite cytochalasin B (CB) disrupt the actin microfilament network by different mechanisms, and increase outflow facility similarly in live monkeys. Their combined effect has therefore determined on total outflow facility in cynomolgus monkeys by 2-level constant pressure perfusion. (1) After unilateral anterior chamber (AC) bolus injection of H-7 [10 micrometers, 100 micrometers (subthreshold for increasing facility when given alone) or 500 micrometers (just-threshold)] followed by bilateral AC bolus injection of CB [2 micrograms (strong but submaximal for increasing facility when given alone)], no significant difference between eyes was observed. (2) After bilateral AC exchange with a subthreshold dose of H-7 (10 micrometers) followed by unilateral AC bolus injection of a subthreshold dose of CB (0.02, 0.05, 0.1 or 0.5 microgram), 10 micrometers H-7 plus 0.1 or 0.5 microgram CB increased facility by approximately 40 or 80% compared to 10 micrometers H-7 alone. (3) After bilateral AC exchange with a maximal dose of H-7 (300 micrometers), followed by unilateral AC bolus injection of a subthreshold dose of CB (0.1 or 0.5 microgram), 300 micrometers H-7 plus 0.5 microgram CB increased outflow facility by 47% compared to 300 micrometers H-7 alone. (4) After unilateral AC exchange with a maximal dose of H-7 (300 micrometers) followed by bilateral AC bolus injection of a near-maximal dose of CB (2 micrograms), 300 micrometers H-7 plus 2 micrograms CB increased the facility by 67% compared to 2 micrograms CB alone. The significant effect of combined subthreshold doses of H-7 and CB on outflow facility, the potentiation of the facility-increasing effect of a maximal H-7 dose by both subthreshold and near-maximal CB doses, and the known cytoskeletal effects of both compounds, may suggest that both increase facility by disrupting actin filaments in the trabecular meshwork.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1999

Localization of changes in beta-actin expression in remodeled canine myocardium.

Beta-actin is a cytoskeletal protein that has been implicated as a potentially important mediator of the growth, signaling, migration, and remodeling of cells. Beta-actin is upregulated in remodeling myocardium in response to either pressure or volume overload. The cellular localization of this response has, however, not been determined and is a necessary first step to begin to clarify the role of beta-actin in myocardial remodeling. Here we demonstrate that beta -actin protein was confined primarily to the cardiac interstitium using immunofluorescent and immunohistochemical staining. Furthermore, both staining and immunoblotting showed markedly increased beta-actin protein in myocardium within 24 h of either regional left ventricular damage or chronic volume overload. More importantly, this increase persisted up to 90 days in both models. Double staining showed co-localization of beta-actin protein and von Willebrand factor, a specific endothelial cell marker. These results suggest that increased beta-actin expression predominantly localized in cardiac interstitial cells, including endothelial cells. The increased beta-actin could be due to either proliferation of the interstitial cells or upregulation of the beta-actin gene.

Actins↗
PubMed1999

Modality-specific frontal and parietal areas for auditory and visual spatial localization in humans.

Although the importance of the posterior parietal and prefrontal regions in spatial localization of visual stimuli is well established, their role in auditory space perception is less clear. Using positron emission tomography (PET) during auditory and visual spatial localization in the same subjects, modality-specific areas were identified in the superior parietal lobule, middle temporal and lateral prefrontal cortices. These findings suggest that, similar to the visual system, the hierarchical organization of the auditory system extends beyond the temporal lobe to include areas in the posterior parietal and prefrontal regions specialized in auditory spatial processing. Our results may explain the dissociation of visual and auditory spatial localization deficits following lesions involving these regions.

Adult↗
PubMed1999

Dual streams of auditory afferents target multiple domains in the primate prefrontal cortex.

'What' and 'where' visual streams define ventrolateral object and dorsolateral spatial processing domains in the prefrontal cortex of nonhuman primates. We looked for similar streams for auditory-prefrontal connections in rhesus macaques by combining microelectrode recording with anatomical tract-tracing. Injection of multiple tracers into physiologically mapped regions AL, ML and CL of the auditory belt cortex revealed that anterior belt cortex was reciprocally connected with the frontal pole (area 10), rostral principal sulcus (area 46) and ventral prefrontal regions (areas 12 and 45), whereas the caudal belt was mainly connected with the caudal principal sulcus (area 46) and frontal eye fields (area 8a). Thus separate auditory streams originate in caudal and rostral auditory cortex and target spatial and non-spatial domains of the frontal lobe, respectively.

Acoustic Stimulation↗
PubMed1999

Advances in glaucoma diagnosis and therapy for the next millennium: new drugs for trabecular and uveoscleral outflow.

Advances in our understanding of the physiology and molecular biology of the trabecular and uveoscleral outflow pathways of the eye will lead to the development of new approaches for glaucoma therapy. Therapies of the future will target the structures and enzymes involved in maintaining cell shape and cell-cell and cell-extracellular matrix interactions. Altering the extracellular matrix in the ciliary muscle has been important in the intraocular pressure lowering effects of prostaglandins and will be developed further as an approach to enhancing outflow through the trabecular meshwork. Gene therapy may be used to enhance or suppress the endogenous targets that are ultimately responsible for the outflow enhancement triggered by these agents.

Animals↗