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R Liu

Publications and source records attributed to R Liu.

At least 73 records · Page 4Linked to original sources
PubMed2001

Brimonidine and inhibition of nitrite production in isolated porcine ciliary processes.

PURPOSE: To investigate whether the alpha 2-adrenoreceptor agonist brimonidine (a drug that decreases intraocular pressure in part by reducing aqueous humor production) can inhibit the production of nitrite induced by forskolin in isolated porcine ciliary processes. METHODS: Nitrite (a metabolite of nitric oxide) was measured (Griess reaction) before and two hours after exposure to the adenylcyclase activator forskolin (0.1 microM) in the presence or in the absence of the brimonidine (10 microM) and/or the alpha 2-adrenoreceptor antagonist yohimbine (10 microM). RESULTS: The increase of nitrite production evoked by forskolin (139 +/- 9%) was significantly (P < 0.01) inhibited by brimonidine (108 +/- 6%). The inhibitory effect of brimonidine on the increase of nitrite production induced by forskolin was significantly (P < 0.01) reversed by yohimbine (136 +/- 7%). CONCLUSIONS: The results of this pilot study suggest that brimonidine inhibits the production of nitrite evoked by forskolin through a mechanism that could involve alpha 2-adrenoreceptor activation in isolated porcine ciliary processes.

Adrenergic alpha-Agonists↗
PubMed2001

Topical ocular instillation of nitric oxide synthase inhibitors and intraocular pressure in rabbits.

PURPOSE: It has been reported that intravenous injection of the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl esther (L-NAME) causes a rapid decrease of intraocular pressure (IOP) in rabbits. This study investigates the effect of topical ocular application of different NOS inhibitors on a raise of IOP induced by an acute water intake (rabbit water loading model). METHODS: Forty New Zealand (albino) male rabbits received randomly (within thirty minutes) in their right eye three 50 microliters installations of either 0.9% NaCl, 0.5% timolol maleate (beta-adrenoreceptor antagonist), 0.5% 7-nitroindazole (7-NI; NOS inhibitor), 0.5% L-NAME, or 0.5% 2-amino-5,6-dihydro-6-methyl-1,3,-thiazine (AMT; NOS inhibitor) before an oral water gavage (60 ml/kg). IOP was measured (TonoPen) before and after topical instillation (time 0), and then 15, 30, 60, 90, and 120 minutes after water intake. RESULTS: In right eyes, the area under the curve (AUC) of the IOP difference versus time (arbitrary units) was 527 +/- 284 for NaCl, 255 +/- 178 for timolol, 466 +/- 242 for 7-NI, 604 +/- 195 for L-NAME, and 394 +/- 202 for AMT. Values of AUC were only significantly lower (p < 0.05) in the timolol-treated group. In left eyes, no significant difference (p > 0.05) could be observed in values of AUC between groups. CONCLUSIONS: Under the present experimental conditions (including concentration and bioavailability of the drugs used), topical application of the NOS inhibitors 7-NI, L-NAME, and AMT does not prevent an IOP increase induced by water intake in rabbits.

Adrenergic beta-Antagonists↗
PubMed2001

Modulation of Na/K-ATPase activity by isoproterenol and propranolol in human non-pigmented ciliary epithelial cells.

PURPOSE: The present study investigates whether beta-adrenoreceptor agents such as isoproterenol and propranolol can regulate Na(+)-K(+)-ATPase activity in cultured human non-pigmented ciliary epithelial cells. METHODS: Human non-pigmented ciliary epithelial cells (ODM2) were grown to confluence. The active ion transport mediated by the Na(+)-K(+)-ATPase was evaluated by measuring ouabain-sensitive rubidium (Rb+) uptake. In a first set of experiments, cells were exposed to the beta-adrenoreceptor agonist isoproterenol (0.01-10 microM). In a second set of experiments, cells were exposed to isoproterenol (1 microM) in the presence of different concentrations of the beta-adrenoreceptor antagonist propranolol (0.01, 0.1, 1 microM). RESULTS: In a concentration-dependent manner, isoproterenol induced an increase in Na(+)-K(+)-ATPase activity. The maximal Na(+)-K(+)-ATPase activity was observed at a concentration of 1 microM of isoproterenol (283 +/- 58%, P < 0.001). The increase in Na(+)-K(+)-ATPase activity evoked by isoproterenol (1 microM) was inhibited. In a concentration dependent manner, by propranolol (maximum: 659 +/- 39 vs. 141 +/- 42 pM/mg protein/min, P < 0.01). CONCLUSION: The beta-adrenoreceptor agents isoproterenol and propranolol are apparently able to modulate Na(+)-K(+)-ATPase activity in cultured human non-pigmented ciliary epithelial cells.

Adrenergic beta-Agonists↗
PubMed2001

Conformational model for binding site recognition by the E.coli MetJ transcription factor.

MOTIVATION: Current methods for identifying sequence specific binding sites in DNA sequence using position specific weight matrices are limited in both sensitivity and specificity. Double strand DNA helix exhibits sequence dependent variations in conformation. Interactions between macromolecules result from complementarity of the two tertiary structures. We hypothesize that this conformational variation plays a role in transcription factor binding site recognition, and that the use of this structure information will improve the predictive power of transcription factor binding site models. RESULTS: Conformation models for the sequence dependence of DNA helix distortion have been developed. Using our conformational models, we defined a tertiary structure template for the met operon repressor MetJ binding site. Both naturally occurring sites and precursor binding sites identified through in vitro selection were used as the basis for template definition. The conformational model appears to recognize features of protein binding sites that are distinct from the features recognized by primary sequence based profiles. Combining the conformational model and primary sequence profile yields a hybrid model with improved discriminatory power compared with either the conformational model or sequence profile alone. Using our hybrid model, we searched the E.coli genome. We are able to identify the documented MetJ sites in the promoter regions of metA, metB, metC, metR and metF. In addition, we find several novel loci with characteristics suggesting that they are functional MetJ repressor binding sites. Novel MetJ binding sites are found upstream of the metK gene, as well as upstream of a gene, abc, a gene that encodes for a component of a multifunction transporter which may transport amino acids across the membrane. The false positive rate is significantly lower than the sequence profile method. AVAILABILITY: The programs of implementation of this algorithm are available upon request. The list of crystal structures used for compiling the mean base step parameters of DNA is available by anonymous ftp at http://stateslab.wustl.edu/pub/helix/StructureList.

Bacterial Proteins↗
PubMed2001

Role of potassium channels in isoflurane- and sevoflurane-induced attenuation of hypoxic pulmonary vasoconstriction in isolated perfused rabbit lungs.

BACKGROUND: Although potassium channels are thought to be responsible for the initiation of hypoxic pulmonary vasoconstriction (HPV), their role in the HPV-inhibitory effect of volatile anesthetics is unclear. The current study tested if the HPV-inhibitory effect of isoflurane and sevoflurane can be affected by changing the potassium-channel opening status with specific potassium-channel inhibitors in isolated rabbit lungs. METHODS: Isolated rabbit lungs were divided into eight groups (n = 6 each in isoflurane groups and n = 8 in sevoflurane groups): those receiving no inhibitor treatment = control-isoflurane and control-sevoflurane groups; those treated with an adenosine triphosphate-sensitive potassium (K(ATP))-channel inhibitor, glibenclamide = glibenclamide-isoflurane and glibenclamide-sevoflurane groups; those treated with a high-conductance calcium-activated potassium (K(Ca))-channel inhibitor, iberiotoxin = iberiotoxin-isoflurane and iberiotoxin-sevoflurane groups; and those treated with a voltage-sensitive potassium (Kv)-channel inhibitor, 4-aminopyridine = 4-aminopyridine-isoflurane and 4-aminopyridine-sevoflurane groups. The effect of anesthetic on HPV was tested by exposure of the lungs to isoflurane at a concentration of 0, 0.5, 1, or 2 minimum alveolar concentration, or to sevoflurane at a concentration of 0, 0.5, 1, or 1.62 minimum alveolar concentration. The relation between anesthetic concentrations and the HPV response was analyzed by the Wagner equation. RESULTS: The inhibition of Kv channels by 4-aminopyridine and K(Ca) channels by iberiotoxin augmented the HPV response. The isoflurane-induced attenuation of HPV was attenuated by voltage-sensitive potassium-channel inhibition with 4-aminopyridine, potentiated by K(Ca)-channel inhibition with iberiotoxin, but not affected by K(ATP)-channel inhibition with glibenclamide. The sevoflurane-induced attenuation of HPV was not affected by any of the potassium-channel inhibitors. CONCLUSIONS: Isoflurane may modulate the HPV response partially through K(Ca) and Kv channels, but sevoflurane may attenuate the HPV response through other pathways rather than through the currently investigated potassium channels in isolated rabbit lungs.

Algorithms↗
PubMed2001

Submandibular gland transfer: a new method of preventing radiation-induced xerostomia.

OBJECTIVE: Radiation-induced xerostomia is a significant morbidity of radiation therapy in the management of patients with head and neck cancers. We have recently reported a method of transfer of one submandibular gland to the submental space in a small pilot series of eligible surgical patients. The submental space was shielded during postoperative radiation therapy. The transferred gland continued to function after the completion of radiation therapy and none of the patients developed xerostomia. The purpose of this article is to present the technique of submandibular gland transfer in detail and to evaluate the postoperative survival and function of the transferred submandibular glands. DESIGN: Prospective clinical trial. METHODS: The submandibular gland was transferred on eligible patients as part of their surgical intervention. The patients were followed clinically, with salivary flow and radioisotope studies. RESULTS: We performed the surgical transfer of the submandibular salivary gland in 24 of 25 patients placed on the protocol. All the glands survived transfer and functioned well postoperatively as demonstrated on the salivary flow and the radioisotope studies. The surgical transfer was relatively simple and added 45 minutes to the surgical procedure. There were no complications attributed to the submandibular gland transfer. CONCLUSIONS: We have successfully demonstrated that the submandibular gland can be surgically transferred to the submental space with its function preserved. The gland seems to continue functioning even after radiation therapy with the appropriate shielding. This surgical transfer procedure has the potential to change the way we currently manage patients with head and neck cancer.

Adult↗
PubMed2001

Interdigital pair bonding for high frequency (20-50 MHz) ultrasonic composite transducers.

Interdigital pair bonding is a novel methodology that enables the fabrication of high frequency piezoelectric composites with high volume fractions of the ceramic phase. This enhancement in ceramic volume fraction significantly reduces the dimensional scale of the epoxy phase and increases the related effective physical parameters of the composite, such as dielectric constant and the longitudinal sound velocity, which are major concerns in the development of high frequency piezoelectric composites. In this paper, a method called interdigital pair bonding (IPB) is used to prepare 1-3 piezoelectric composite with a pitch of 40 microns, a kerf of 4 microns, and a ceramic volume fraction of 81%. The composites prepared in this fashion exhibited a very pure thickness-mode resonance up to a frequency of 50 MHz. Unlike the 2-2 piezoelectric composites with the same ceramic and epoxy scales developed earlier, the anticipated lateral modes between 50 to 100 MHz were not observed in the current 1-3 composites. The mechanisms for the elimination of the lateral modes at high frequency are discussed. The effective electromechanical coupling coefficient of the composite was 0.72 at a frequency of 50 MHz. The composites showed a high longitudinal sound velocity of 4300 m/s and a high clamped dielectric constant of 1111 epsilon 0, which will benefit the development of high frequency ultrasonic transducers and especially high frequency transducer arrays for medical imaging.

Ceramics↗
PubMed2001

Mice lacking the Nkx6.2 (Gtx) homeodomain transcription factor develop and reproduce normally.

The Nkx homeobox genes are expressed in a variety of developing tissues and have been implicated in controlling tissue patterning and cell differentiation. Expression of Nkx6.2 (Gtx) was previously observed in the embryonic neural tube, testis, and differentiating oligodendrocytes. To investigate the role of Nkx6.2 in the control of cell specification and differentiation, we generated mice with null mutations in Nkx6.2 using the standard gene targeting approach. Null mutant mice were viable and fertile without apparent histological and immunohistochemical changes in the central nervous systems and testis. The absence of detectable phenotypes suggests a redundant function of Nkx6.2 in mouse development.

Animals↗
PubMed2001

Facial nerve schwannoma: surgical excision versus conservative management.

Facial nerve schwannomas are slow-growing tumors that may involve any part of the facial nerve. When they present with moderate to total facial palsy, complete resection is clearly indicated. However, in cases with mild or no facial dysfunction, the best course of treatment is less obvious. A series of 22 patients with facial nerve schwannoma is presented, of whom 12 underwent definitive excision and 10 were managed more conservatively. The best postoperative facial function in the group who had tumor removal was a House-Brackmann grade III, while 8 of the conservatively treated group had normal facial function up to 10 years after presentation. As well, no significant tumor growth was noted on serial radiologic imaging of those being observed. Delaying surgical resection of facial nerve schwannomas may allow patients to retain normal facial function indefinitely.

Adolescent↗
PubMed2001

Pectoralis major myocutaneous pedicled flap in head and neck reconstruction: retrospective review of indications and results in 244 consecutive cases at the Toronto General Hospital.

The pectoralis major myocutaneous pedicled flap (PMMPF) has been considered to be the "workhorse" of pedicled flaps for head and neck reconstruction, and several series of PMMPF procedures have been reported in the literature. Between 1983 and 1997, 244 reconstruction procedures using the PMMPF were carried out on 229 patients by the Otolaryngology-Head and Neck Surgery Department at the Toronto General Hospital. Pectoralis major myocutaneous pedicled flap reconstructions were completed after ablation of cancer in the following sites: oral cavity, 113; oropharynx/hypopharynx, 50; larynx, 59; and other, 21. The locations of reconstruction were oral cavity, 121; pharynx, 74; and neck or face, 50. Of the 244 cases, 202 were carried out as primary reconstructive procedures, whereas 42 flaps were "salvage" procedures (reconstruction after fistula, flap failure, osteoradionecrosis, and internal jugular vein rupture). Eighty-five cases (35%) were affected by complications such as dehiscence, infection, hematoma, seroma, partial flap failure, total flap failure, fistula, and donor site complications. The duration of admission for cases with complications was longer, and higher complication rates were associated with salvage procedures, number of comorbidities, number of pack-years of cigarettes smoked, and oral cavity reconstructions. This series of consecutive PMMPF procedures is the largest reported to date.

Canada↗
PubMed2001

Expression of the melanin-concentrating hormone receptor in porcine and human ciliary epithelial cells.

PURPOSE: To evaluate whether the receptors for melanin-concentrating hormone (MCH) and its functional antagonist alpha-melanocyte-stimulating hormone (alpha-MSH) are expressed in the ciliary epithelium. Furthermore, to examine whether MCH, a neuropeptide involved in fluid and electrolyte homeostasis, may influence ion flux mediated by Na,K (adenosine triphosphatase)-ATPase in a ciliary epithelial cell line. METHODS: Expression of MCH receptors (MCH-R) and alpha-MSH receptors (MSH-R) on primary porcine ciliary pigmented epithelial (PE) cells and on a human nonpigmented ciliary epithelial (NPE) cell line, ODM-2 was investigated by radioligand binding studies and reverse transcription-polymerase chain reaction (RT-PCR). The MCH-R was further characterized by photocrosslinking. Influence of MCH on Na, K-ATPase activity was evaluated by an Rb(+) transport assay. RESULTS: MCH-R expression was observed at both the mRNA and protein levels in PE and NPE cells. In contrast, MSH-Rs were not detectable. At the mRNA level, expression of slc-1 was shown and with crosslinking, a 44-kDa protein was labeled. MCH showed no effect on Na,K-ATPase activity of NPE cells. CONCLUSIONS: The presence of MCH-R in ciliary epithelial cells of both human and porcine origin but the absence of MSH-Rs indicates that in these cells, MCH and alpha-MSH do not form a functionally antagonistic hormonal pair as they do in several other systems. Although effects of MCH on intestinal water and ion transport have been documented, a direct control of Na,K-ATPase activity was not detected in human NPE cells in vitro.

Animals↗
PubMed2001

Drug transport by reconstituted P-glycoprotein in proteoliposomes. Effect of substrates and modulators, and dependence on bilayer phase state.

The P-glycoprotein multidrug transporter (Pgp) is an active efflux pump for chemotherapeutic drugs, natural products and hydrophobic peptides. Pgp is envisaged as a 'hydrophobic vacuum cleaner', and drugs are believed to gain access to the substrate binding sites from within the membrane, rather than from the aqueous phase. The intimate association of both Pgp and its substrates with the membrane suggests that its function may be regulated by the biophysical properties of the lipid bilayer. Using the high affinity fluorescent substrate tetramethylrosamine (TMR), we have monitored, in real time, transport in proteoliposomes containing reconstituted Pgp. The TMR concentration gradient generated by Pgp was collapsed by the addition of either the ATPase inhibitor, vanadate, or Pgp modulators. TMR transport by Pgp obeyed Michaelis--Menten kinetics with respect to both of its substrates. The Km for ATP was 0.48 mM, close to the K(m) for ATP hydrolysis, and the K(m) for TMR was 0.3 microM. TMR transport was inhibited in a concentration-dependent fashion by verapamil and cyclosporin A, and activated (probably by a positive allosteric effect) by the transport substrate colchicine. TMR transport by Pgp reconstituted into proteoliposomes composed of two synthetic phosphatidylcholines showed a highly unusual biphasic temperature dependence. The rate of TMR transport was relatively high in the rigid gel phase, reached a maximum at the melting temperature of the bilayer, and then decreased in the fluid liquid crystalline phase. This pattern of temperature dependence suggests that the rate of drug transport by Pgp may be dominated by partitioning of drug into the bilayer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

[Analysis of apoA IV gene VNTR polymorphism in Chinese endogenous hypertriglyceridemics].

OBJECTIVE: To search the variation of apoA IV gene and its relation to endogenous hypertriglyceridemia (HTG) in Chinese population. METHODS: Forty- seven endogenous hypertriglyceridemics and 48 healthy subjects from a population of Chinese Han nationality in Chengdu area were studied using sequencing of apoA IV gene amplified by polymerase chain reaction (PCR). RESULTS: The frequency of (CTGT)(3) allele in Chinese control group was significantly different from that reported in German Caucasians (0.253 vs 0.607, P<0.01) and in Italian Caucasians (0.253 vs 0.522, P<0.01), but not different from that reported in Japanese (0.253 vs 0.262, P>0.05). The frequency of (CTGT)(3) allele showed no significant difference between normal control and HTG groups(0.223 vs 0.281,P>0.05). In the healthy control group, the subjects with genotype 3/3 of VNTR site had a higher serum mean concentration of LDLC as compared to those with genotype 3/4 (3.698 +/- 0.67 mmol/L vs 2.974 +/- 0.54 mmol/L, P<0.05). CONCLUSION: The results suggest that VNTR polymorphism in apoA IV gene is associated with healthy control subjects to some extent in Chinese population.

Adult↗
PubMed2001

Lovastatin increases nitric oxide synthesis in IL-1 beta-stimulated smooth muscle cells.

OBJECTIVE: Nitric oxide (NO) production by inducible NO synthase (iNOS) may play an important role in the pathogenesis of atherosclerosis. Although lovastatin has been shown to reduce the progression of atherosclerosis, it is not known whether it regulates NO production. We investigated the effects of lovastatin on NO synthesis and the mechanisms by which lovastatin exerts its effects in rat vascular smooth muscle cells. METHODS: Primary cultures of the vascular smooth muscle cells were obtained from the media of the thoracic aorta of Sprague Dawley rats (200-250 g). Nitrite levels in the culture medium of rat vascular smooth muscle cells were determined colorimetrically. RESULTS: Lovastatin (10(-5) mol/L) significantly increased interleukin-1 beta (IL-1 beta, 10 ng/mL)-induced nitrite accumulation in a time (0-24 hours)-dependent manner. Exogenous mevalonate and geranylgeranyl-pyrophosphate completely reversed the stimulatory effects of lovastatin on nitrite production. Furthermore, inhibition of Rho by C3 exoenzyme mimicked the increase in IL-1 beta-induced nitrite accumulation induced by lovastatin in the vascular smooth muscle cells. CONCLUSION: These results demonstrate that lovastatin up-regulates NO formation in rat vascular smooth muscle cells stimulated by IL-1 beta, and the effect may be associated with the inhibition of Rho activity.

Animals↗
PubMed2001

Src family protein tyrosine kinase signaling mediates monosodium urate crystal-induced IL-8 expression by monocytic THP-1 cells.

Neutrophil-dependent inflammation dependent on monosodium urate (MSU) crystal-induced IL-8 expression occurs in gout. MSU crystals activate phagocyte Src family tyrosine kinases and the serine/threonine kinase p70s6k. Thus, using monocytic THP-1 cells, we assessed the potential for Src family kinases and p70s6k to mediate MSU-induced IL-8 expression. MSU crystals induced phosphorylation of p70s6k and the Src kinases c-Src, Lyn, Hck, and Fyn. IL-8 expression was attenuated more by the Src kinase inhibitor PP1 than by the p70s6k inhibitor rapamycin. PP1 inhibited crystal-induced phosphorylation of ERK1/2 and IkappaBalpha and suppressed IkappaB kinase (IKK) activation and NF-kappaB binding to the IL-8 promoter, signals that mediate MSU-induced IL-8 expression. Transfection of the native Src inhibitor, C-terminal Src kinase (Csk), also suppressed crystal-induced c-Src, ERK1/2, and IkappaBalpha phosphorylation and IL-8 expression. We conclude that Src family tyrosine kinase signaling plays a significant role in MSU crystal-induced IL-8 expression via stimulation of ERK1/2 pathway and NF-kappaB activation.

Cell Line↗
PubMed2001

[Gap formation features of humid evergreen broad-leaved forest in central subtropical Wawushan Mountain, Sichuan Province, China].

The primary and secondary subtropical evergreen broad-leaved forests at an altitude of 1720-1750 m in Mt. Wawushan National Forest Park, southwestern China investigated to analyze their canopy gap formation characteristics. The sampling method and canopy formation causes were also discussed. In secondary evergreen broad-leaved forest, the gap density was surprisingly only 9 per hm2 and the size of all gaps was, no more than 10 m2. Almost every gap had only one gap maker, and the gap makers often died standing by suppression. Accordingly successful natural regeneration is difficult in small gap, due to the rapidly lateral growth of canopy trees. In primary evergreen broad-leaved forest, the gap density was 15 per hm2, and 56% of the gaps had an area of no more than 40 m2. The largest gap had an area of 256 m2. The canopy gap accounted for 11.1% and expended gap occupied 19.8% of land area in the forest. Median area of canopy gaps and expended gaps was 59 and 105 m2, respectively. Most gaps had more than one gap maker, and gap makers died falling and were often from mortality events separated in time. Most gaps aged over 10 yr and a few were formed recently and the estimated gap formation rate was 0.01 per year. According to falling direction of trees and the relations with growth process, slope aspect and wind, we deduced gap-maker death resulted from integrated influence among topography, climate particular in wind, tree growth characteristics, and interactions of population under competition. Adapting method of plot sampling and projection drawing used in the paper can improve investigation accuracy and help improving comparison of results in different investigation area.

Altitude↗
PubMed2001

[The accuracy analysis on Kriging estimation of the water quality parameters of lakes].

The spatial distribution of pollutants in lakes is required in the study of lakes. The key issue is the spatial optimal estimation. This paper elaborated the characteristics of Kriging variance and analyzed systematically the accuracy of Kriging estimation on water quality parameters of lakes in the light of a practical example of Taihu Lake. The accuracy of estimation was determined by many factors such as variogram, distribution of sampling sites and so on, and was not related to the values of sampling data.

Fresh Water↗