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Hua Yang

Publications and source records attributed to Hua Yang.

At least 73 records · Page 4Linked to original sources
PubMed2005

A simulation study on the Ca2+-independent but voltage-dependent exocytosis and endocytosis in dorsal root ganglion neurons.

In patch-clamped somata of dorsal root ganglion (DRG) neurons, two types of secretion have been proposed: Ca(2+)-dependent secretion and Ca(2+)-independent but voltage-dependent secretion (CIVDS). The Ca(2+)-induced and the depolarization-induced membrane capacitance (C(m)) increases contribute 80 and 20% to the total C(m) increase, respectively (Zhang and Zhou in Nat Neurosci 5:425, 2002). In order to explore the mechanism of the voltage-dependent C(m) change (DeltaC(m)), we constructed a model with sequential states. The simulation with this model closely approximates all the experimental data. The model predicts that the majority of fusion events (approximately 80%) are so-called "kiss-and-run" events, which account for the fast recovery or the rapid retrieval feature of the signals. The remaining 20% are attributed to full fusion events, which account for a slow retrieval feature. On the basis of the model, one mechanism of the activity-dependent endocytosis has revealed a differential distribution of vesicles between the kiss-and-run and full fusion states at different stimulation frequencies. The quantitative model presented in this study may help us to understand the mechanism of the CIVDS and the tightly coupled endocytosis found in mammalian DRG neurons.

Animals↗
PubMed2005

The high-throughput protein-to-structure pipeline at SECSG.

Using a high degree of automation, the crystallography core at the Southeast Collaboratory for Structural Genomics (SECSG) has developed a high-throughput protein-to-structure pipeline. Various robots and automation procedures have been adopted and integrated into a pipeline that is capable of screening 40 proteins for crystallization and solving four protein structures per week. This pipeline is composed of three major units: crystallization, structure determination/validation and crystallomics. Coupled with the protein-production cores at SECSG, the protein-to-structure pipeline provides a two-tiered approach for protein production at SECSG. In tier 1, all protein samples supplied by the protein-production cores pass through the pipeline using standard crystallization screening and optimization procedures. The protein targets that failed to yield diffraction-quality crystals (resolution better than 3.0 A) become tier 2 or salvaging targets. The goal of tier 2 target salvaging, carried out by the crystallomics core, is to produce the target proteins with increased purity and homogeneity, which would render them more likely to yield well diffracting crystals. This is performed by alternative purification procedures and/or the introduction of chemical modifications to the proteins (such as tag removal, methylation, surface mutagenesis, selenomethionine labelling etc.). Details of the various procedures in the pipeline for protein crystallization, target salvaging, data collection/processing and high-throughput structure determination/validation, as well as some examples, are described.

Crystallization↗
PubMed2005

Systemic transforming growth factor-beta1 gene therapy induces Foxp3+ regulatory cells, restores self-tolerance, and facilitates regeneration of beta cell function in overtly diabetic nonobese diabetic mice.

BACKGROUND: Type 1 diabetes results from auto-aggressive T-cell-mediated destruction of beta cells of the pancreas. Recent data suggest that restoration of self-tolerance may facilitate islet-cell regeneration/recovery. In view of the immunoregulatory activity of transforming growth factor (TGF)-beta1, we investigated whether systemic TGF-beta1 gene therapy blocks islet destructive autoimmunity and facilitates regeneration of beta-cell function in overtly diabetic nonobese diabetic (NOD) mice. METHODS: We used site-directed mutagenesis to create cysteine to serine mutation at sites 224 and 226 and constructed a replication deficient adenovirus (Ad) vector encoding active form of human TGF-beta1 (Ad-hTGF-beta1). Overtly diabetic NOD mice received intravenous injection of Ad-hTGF-beta1. Seven to 14 days after the injection, the mice received transplants with 500 syngeneic islets under the kidney capsule. Islet-graft survival and regeneration of endogenous beta-cell function were examined. RESULTS: Syngeneic islet grafts failed by day 17 in all untreated mice, whereas Ad-hTGF-beta1 therapy prolonged survival of islet grafts. Islet grafts from treated mice showed well-preserved islets with a peri-islet infiltrate primarily of CD4+ T cells and expression of CD25 and Foxp3. Systemic TGF-beta1 gene therapy was associated with islet regeneration in the native pancreas. Native pancreas of treated mice revealed islets staining strongly for insulin. Similar to what was found in the syngeneic islet graft, there were well-demarcated peri-islet infiltrates that were positive for CD4, TGF-beta1, and Foxp3. CONCLUSIONS: Our data demonstrate that systemic TGF-beta1 gene therapy blocks islet destructive autoimmunity, facilitates islet regeneration, and cures diabetes in diabetic NOD mice.

Animals↗
PubMed2005

Measurement of apoptosis of intact human islets by confocal optical sectioning and stereologic analysis of YO-PRO-1-stained islets.

Apoptosis is an established pathway for islet cell demise. Current protocols for assessment of islet cell apoptosis are time-consuming (as with terminal deoxynucleotide transferase-mediated dUTP nick-end labeling reaction) and involve disruption of the islet architecture (as with flow cytometry) or destruction of cell integrity (as with enzyme-linked immunosorbent assay). The membranes of apoptotic cells, but not those of live cells, are permeant to the DNA-intercalant dye YO-PRO-1. We report a novel methodology for the rapid quantification of apoptosis of human islets: confocal laser optical sectioning and stereologic analysis of intact human islets stained with YO-PRO-1 and Hoechst 33342. The advantages include (1) rapid quantification of apoptosis without disrupting islet architecture and (2) identification of significant heterogeneity in the extent of apoptosis among islets from the same isolate. Confocal laser scanning microscopy microscopic imaging of YO-PRO-1-stained islets may advance investigation of islet cell apoptosis and help develop islet parameters predictive of posttransplant function.

Apoptosis↗
PubMed2005

Voltammetric study of extracellular dopamine near microdialysis probes acutely implanted in the striatum of the anesthetized rat.

Establishing in vivo microdialysis methods for the quantitative determination of dopamine concentrations in the extracellular space of the brain is an important yet challenging objective. The source of the challenge is the difficulty in directly measuring the microdialysis recovery of dopamine during an in vivo experiment. The recovery value is needed for quantitative microdialysis, regardless of whether conventional or no-net-flux methods are used. Numerical models of microdialysis that incorporate both diffusion and active transport processes suggest that dopamine recovery is strongly affected by processes occurring in the tissue closest to the probe. Some evidence suggests that the tissue adjacent to the probe becomes disrupted during probe implantation. Hence, the objective of the present study was to further identify whether the tissue adjacent to the probe is disrupted and, if so, whether that disruption might affect dopamine recovery. The experiments were conducted with microdialysis probes implanted acutely in the striatum of rats anesthetized with chloral hydrate. Carbon fiber voltammetric microelectrodes were used to monitor extracellular dopamine at three sites near the probes; immediately adjacent to the probe, 220-250 microm from the probe, and 1 mm from the probe. Probes were lowered slowly over a 30 min period, so that dialysate dopamine levels were stable, in the low nanomolar range, and partially TTX-sensitive by the time experiments began. Starting 2h after probe implantation, dopamine was monitored by fast-scan cyclic voltammetry during electrical stimulation of the medial forebrain bundle and during administration of the dopamine uptake inhibitor, nomifensine. The findings of this study show that a gradient of dopamine release and uptake activity extends at least 220 microm from microdialysis probes implanted acutely in the striatum of the anesthetized rat.

Anesthetics, Intravenous↗
PubMed2005

PKC-induced sensitization of Ca2+-dependent exocytosis is mediated by reducing the Ca2+ cooperativity in pituitary gonadotropes.

The highly cooperative nature of Ca2+-dependent exocytosis is very important for the precise regulation of transmitter release. It is not known whether the number of binding sites on the Ca2+ sensor can be modulated or not. We have previously reported that protein kinase C (PKC) activation sensitizes the Ca2+ sensor for exocytosis in pituitary gonadotropes. To further unravel the underlying mechanism of how the Ca2+ sensor is modulated by protein phosphorylation, we have performed kinetic modeling of the exocytotic burst and investigated how the kinetic parameters of Ca2+-triggered fusion are affected by PKC activation. We propose that PKC sensitizes exocytosis by reducing the number of calcium binding sites on the Ca2+ sensor (from three to two) without significantly altering the Ca2+-binding kinetics. The reduction in the number of Ca2+-binding steps lowers the threshold for release and up-regulates release of fusion-competent vesicles distant from Ca2+ channels.

Animals↗
PubMed2005

Crystal structure of human SCO1: implications for redox signaling by a mitochondrial cytochrome c oxidase "assembly" protein.

Human SCO1 and SCO2 are copper-binding proteins involved in the assembly of mitochondrial cytochrome c oxidase (COX). We have determined the crystal structure of the conserved, intermembrane space core portion of apo-hSCO1 to 2.8 A. It is similar to redox active proteins, including thioredoxins (Trx) and peroxiredoxins (Prx), with putative copper-binding ligands located at the same positions as the conserved catalytic residues in Trx and Prx. SCO1 does not have disulfide isomerization or peroxidase activity, but both hSCO1 and a sco1 null in yeast show extreme sensitivity to hydrogen peroxide. Of the six missense mutations in SCO1 and SCO2 associated with fatal mitochondrial disorders, one lies in a highly conserved exposed surface away from the copper-binding region, suggesting that this region is involved in protein-protein interactions. These data suggests that SCO functions not as a COX copper chaperone, but rather as a mitochondrial redox signaling molecule.

Amino Acid Sequence↗
PubMed2005

AKT/PKB signaling mechanisms in cancer and chemoresistance.

During the past decade, Akt (also known as protein kinase B, PKB) has been extensively studied. It regulates a variety of cellular processes by mediating extracellular (mitogenic growth factor, insulin and stress) and intracellular (altered tyrosine receptor kinases, Ras and Src) signals. Activation of Akt by these signals is via its pleckstrin homology (PH) domain binding to products of phosphatidylinositol 3-kinase (PI3K). This process is negatively regulated by a dual phosphatase PTEN tumor suppressor. Today, more than 30 Akt substrates have been identified. These phosphorylation events mediate the effects of Akt on cell survival, growth, differentiation, angiogenesis, migration and metabolism. Further, PI3K/PTEN/Akt pathway is frequently altered in many human malignancies and overexpression of Akt induces malignant transformation and chemoresistance. Thus, the Akt pathway is a major target for anti-cancer drug development. This review focuses on Akt signaling mechanism in oncogenesis and chemoresistance, and ongoing translational efforts to therapeutically target Akt.

Animals↗
PubMed2005

A novel liquid chromatography/tandem mass spectrometry based depletion method for measuring red blood cell partitioning of pharmaceutical compounds in drug discovery.

A novel liquid chromatography/tandem mass spectrometry (LC/MS/MS)-based depletion method for measuring compound partitioning between human plasma and red blood cells (RBC) in a drug discovery environment is presented. Conventionally, RBC partitioning is determined by separate measurements of drug concentrations in equilibrating plasma and whole blood or RBC using separate standards prepared in their respective matrices, i.e., in plasma and whole blood or RBC lysates. The process is very tedious, labor-intensive, and difficult to automate. In addition, interferences from the heme and other highly abundant cellular composites make the measurement of the drug concentration in whole blood or RBC inevitably variable even with a highly specific LC/MS/MS method. Therefore, there is an imminent need to develop a straightforward and fast method to assess the partitioning of drug-like compounds in RBC. This work describes an LC/MS/MS-based depletion assay that measures the compound concentration in plasma that has been equilibrating with RBC. Compounds were spiked into fresh human whole blood and plasma respectively to a final concentration of 500 nM. Both the spiked whole blood and plasma control were incubated at 37 degrees C for up to 60 min. During the time course, aliquots of plasma and whole blood from both incubation mixtures were sampled at 10 and 60 min. The whole blood samples were centrifuged to yield the plasma. The plasma samples from both incubations were extracted using a protein precipitation method, and analyzed using LC/MS/MS under the multiple-reaction monitoring (MRM) mode. The RBC partitioning ratio was calculated using the analyte peak area responses of the plasma samples through an equation deduced in this work. The method was first tested using two commercial compounds, phenoprobamate and acetazolamide, to determine the optimal incubation conditions and the concentration dependency of the assay. The assay reproducibility was also assessed by three inter-day assays for phenoprobamate. This method was further evaluated using 20 commercial compounds of different classes with a wide range of RBC partitioning coefficients and the results were compared with those reported in the literature. Excellent correlation (R2=0.9396) was found between the measured and literature values. In addition, several proprietary compounds were assayed using both the new and traditional methods and the measured partitioning ratios from the two methods are equivalent. The experiments in this work demonstrate that the LC/MS/MS-based depletion method can provide direct and accurate measurement of RBC partitioning for compounds in drug discovery.

Acetazolamide↗
PubMed2005

Salvaging Pyrococcus furiosus protein targets at SECSG.

Proteins derived from the coding regions of Pyrococcus furiosus are targets for three-dimensional X-ray and NMR structure determination by the Southeast Collaboratory for Structural Genomics (SECSG). Of the 2,200 open reading frames (ORFs) in this organism, 220 protein targets were cloned and expressed in a high-throughput (HT) recombinant system for crystallographic studies. However, only 96 of the expressed proteins could be crystallized and, of these, only 15 have led to structures. To address this issue, SECSG has recently developed a two-tier approach to protein production and crystallization. In this approach, tier-1 efforts are focused on producing protein for new Pfu(italics?) targets using a high-throughput approach. Tier-2 protein production efforts support tier-1 activities by (1) producing additional protein for further crystallization trials, (2) producing modified protein (further purification, methylation, tag removal, selenium labeling, etc) as required and (3) serving as a salvaging pathway for failed tier-1 proteins. In a recent study using this two-tiered approach, nine structures were determined from a set of 50 Pfu proteins, which failed to produce crystals suitable for X-ray diffraction analysis. These results validate this approach and suggest that it has application to other HT crystal structure determination applications.

Archaeal Proteins↗
PubMed2005

Intraocular pressure in Northern China in an urban and rural population: the Beijing eye study.

PURPOSE: To evaluate intraocular pressure (IOP) and its demographic associations in an urban and rural population in Northern China. DESIGN: Population-based cohort study. METHODS: In the Beijing Eye Study, IOP was measured by noncontact pneumatonometry. Mean age was 56.20 +/- 10.59 years (range, 40-101 years). RESULTS: Mean IOP was 16.11 +/- 3.39 mm Hg (median, 16 mm Hg; range, 7-60 mm Hg). In the rural group and the urban population group, respectively, IOP was significantly (P = .016 and P = .029, respectively) lower in the high-age group (>or=75 years) than in the middle-age group (55-64 years). In the rural group, IOP was additionally significantly lower in the age group of 40 to 44 years than in the middle-age group, which suggests a reversed U-like course. A multiple regression analysis revealed that IOP significantly increased with myopia (P = .024), and that it was statistically independent of rural area vs urban area (P = .12) and gender (P = .71). CONCLUSION: In the Northern Chinese population, mean and median of IOP that is measured by pneumatonometry is 16 mm Hg with a normal range (mean +/- two SDs) of 10 to 22 mm Hg. In cross-sectional analysis, IOP slightly increased towards an age of 55 to 64 years and decreased towards higher ages. IOP increased with myopia. It was not associated with rural vs urban region or gender.

Adult↗
PubMed2005

Enlarged left atrial volume in hypertrophic cardiomyopathy: a marker for disease severity.

BACKGROUND: Patients with hypertrophic cardiomyopathy and left atrial (LA) enlargement have increased morbidity and mortality. We analyzed the clinical and echocardiographic factors related to LA enlargement, particularly the degree of left ventricular (LV) hypertrophy and diastolic function. METHODS: A total of 104 patients with hypertrophic cardiomyopathy (age 53 +/- 15 years, 64% men) were divided into two groups based on the indexed LA volume (LAVI) (mL/m2) measured by echocardiography: group A (or smaller LAVI group, n = 43) was defined as LAVI < or = 34 mL/m2; and group B (or larger LAVI group, n = 61) as LAVI > 34 mL/m2. Detailed clinical and echocardiographic data were obtained. LV wall thickness was measured at 15 sites at 3 levels (base, mid, and apex). Diastolic function was assessed from mitral and pulmonary venous inflow velocities and Doppler tissue imaging. RESULTS: Both groups were similar in terms of sex, functional class (1.6 +/- 0.8 vs 1.5 +/- 0.8, group B vs A, P = .64), and incidence of atrial fibrillation (13% vs 5%, P = .19). However, patients of group B had a significantly higher incidence of serious cardiovascular events (16.4% vs 2.3%, group B vs A, P = .024). Both groups had a similar degree of resting LV outflow tract obstruction (19 +/- 30 vs 12 +/- 13 mm Hg, group B vs A, P = .06). However, those in group B had a higher incidence of at least moderate mitral regurgitation (25% vs 5%, group B vs A, P = .007), more LV hypertrophy at 6 LV nonapical wall segments (P < .05-P < .001), and a higher hypertrophy (Wigle) score (6.2 +/- 2.2 vs 4.5 +/- 2.1, group B vs A, P < .001). In addition, patients of group B had a higher incidence of abnormal diastolic filling (57% vs 28%, group B vs A, P = .003), a higher early diastolic velocity/early diastolic mitral annular velocity (10.2 +/- 4.9 vs 7.5 +/- 2.9, group B vs A, P = .003), and a higher calculated LA pressure (14.8 +/- 6.5 vs 11.1 +/- 3.4 mm Hg, group B vs A, P = .0011). CONCLUSIONS: Patients with hypertrophic cardiomyopathy and LA enlargement had more serious cardiovascular events and demonstrated greater LV hypertrophy, more diastolic dysfunction, and higher filling pressures.

Adolescent↗
PubMed2005

Ischemia-induced arrhythmia: the role of connexins, gap junctions, and attendant changes in impulse propagation.

Sudden cardiac death accounts for more than half of all cardiovascular deaths in the US, and a large proportion of these deaths are attributed to ischemia-induced ventricular fibrillation. As such, the mechanisms underlying the initiation and maintenance of these lethal rhythms are of significant clinical and scientific interest. In large animal hearts, regional ischemia induces two phases of ventricular arrhythmia. The first phase (1A) occurs between 5 and 7 min after arrest of perfusion. This phase is associated with membrane depolarization, a mild intracellular and extracellular acidification and a small membrane depolarization. A second phase (1B) of ventricular arrhythmia occurs between 20 and 30 minutes after arrest of perfusion. This phase occurs at a time when ischemia-induced K+ and pH changes are relatively stable. The arrhythmia is presumed to relate to the process of cell-to-cell electrical uncoupling because a rapid increase of tissue impedance precedes the onset of the arrhythmia. Of note is that tissue resistance is primarily determined by the conductance properties of the gap junctions accounting for cell-to-cell coupling. Impulse propagation in heart is determined by active and passive membrane properties. An important passive cable property that is modulated by ischemia is intercellular resistance and is determined primarily by gap junctional conductance. As such changes in Impulse propagation during myocardial ischemia are determined by contemporaneous changes in active and passive membrane properties. Cellular K loss, intracellular and extracellular acidosis and membrane depolarization are important factors decreasing excitatory currents, while the collapse of the extracellular compartment and cell-to-cell electrical uncoupling increase the resistance to current flow. The time-course of cellular coupling is closely linked to a number of physiological processes including depletion of ATP, and accumulation of intracellular Ca2+. Hence, interventions such as ischemic preconditioning attenuate the effect of subsequent ischemia, delay the onset of cell-to-cell electrical uncoupling and likewise delay the onset of ischemia-induced arrhythmia.

Animals↗
PubMed2005

Lack of enteral nutrition--effects on the intestinal immune system.

BACKGROUND: Total parenteral nutrition (TPN) results in a loss of mucosal immune function by alterations in both phenotype and function of intraepithelial lymphocytes (IEL). We hypothesized that the observed changes with TPN administration are caused by the lack of enteral feeding, and not to the TPN solution itself. METHODS: Mice received oral feeding (Control), TPN alone (TPN), or TPN plus oral feeding (TPN+Food). Mice were killed after 7 days, and bacteriological cultures from spleen, liver, and mesenteric lymph nodes obtained, with bacterial translocation (BT) being defined as a positive culture. IEL phenotype was analyzed by flow cytometry. IEL messenger RNA (mRNA) cytokine expression used reverse transcriptase polymerase chain reaction (RT-PCR). Apoptosis was detected by terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) staining. RESULTS: BT significantly (P < 0.05, with analysis of variance [ANOVA]) increased in the TPN group (53%) compared with Control (9%) and TPN+Food (14%) groups. TPN also resulted in a significant (P < 0.01) increase in epithelial cell apoptosis: TPN 7.6 +/- 1.1% versus Control 2.9 +/- 1.1% and TPN+Food 2.1 +/- 0.3% (mean +/- SD). Height of the villus-crypt complex was significantly decreased in TPN mice (315 +/- 16 microm) compared with Control (431 +/- 27 microm) and TPN+Food (421 +/- 26 microm) groups. IEL phenotypes significantly changed with TPN administration: CD4+ CD8- as well as CD4+ CD8+ subpopulations were reduced compared with Control or TPN+Food mice; as were the CD8alphabeta+ thymus-dependent, and CD8+ CD44+ mature IEL. IEL cytokine mRNA expression was also significantly altered with TPN: IL-2 and IL-10 expression declined, and IL-4 IL-6, interferon gamma (IFN-gamma), transforming growth factor beta-1 (TGF-beta1), and tumor necrosis factor-alpha (TNF-alpha) were increased, when compared with Control or TPN+Food mice. CONCLUSIONS: This study demonstrates that the major factor responsible for TPN-induced BT and IEL-changes is the lack of enteral feeding and not the administration of the TPN solution itself.

Animals↗
PubMed2005

Refractive error in urban and rural adult Chinese in Beijing.

PURPOSE: To evaluate refractive error and its demographic associations in an urban and rural population in northern China. DESIGN: Epidemiological study. PARTICIPANTS: The Beijing Eye Study is a population-based cohort study in northern China including 4439 subjects. Excluding pseudophakic and aphakic patients, the present study involved 4319 subjects. It was divided into a rural part (1905 [44.1%] subjects) and an urban part (2414 [55.9%] subjects). Mean age was 55.85+/-10.33 years (range, 40-90). METHODS: Standardized ophthalmologic examination. For statistical analysis, the spherical equivalent was converted to binary variables, and logistic regression was used to investigate the association with continuous or categorical independent variables. MAIN OUTCOME MEASURE: Refractive error. RESULTS: Mean refractive error measured -0.33+/-2.22 diopters (D) (range, -20.88 to +7.88). Myopia of >-0.50 D, -1.0 D, >-6.0 D, and >-8 D, respectively, occurred in 22.9% (95% confidence interval [CI], 21.7-24.2), 16.9% (95% CI, 15.8-18.0), 2.6% (95% CI, 2.2-3.1), and 1.5% (95% CI, 1.1-1.9) of the subjects, respectively. Myopic refractive error was associated significantly with younger age (P<0.001), urban region (vs. rural region) (P<0.001), higher educational background (P<0.001), higher degree of nuclear cataract (P<0.001), decreasing uncorrected visual acuity (UCVA) (P<0.001), decreasing best-corrected visual acuity (BCVA) (P<0.001), and female gender (P<0.001). Prevalence of high myopia (myopic refractive error >-8 D) was associated with age (P<0.001), female gender (P = 0.020), urban region (P = 0.023), and lower BCVA (P<0.001). Mean anisometropia was 1.09+/-2.03 D (median, 0.38; range, 0-22.0). Prevalence of anisometropia of > or =1 D was associated significantly with age (P<0.001), refractive error (P<0.001), BCVA (P<0.001), and region (P<0.001). Mean astigmatic error measured 0.62+/-0.90 D (median, 0.25; range, 0-7.50). Astigmatism of > or =1 D was associated significantly with age (P<0.001), lower UCVA (P = 0.003), lower BCVA (P<0.001), urban area (P<0.001), and degree of cortical cataract (P = 0.027). CONCLUSIONS: As in other population-based studies on Chinese, myopia was more prevalent in younger subjects. Myopia was associated with urban region, educational background, female gender, decreasing visual acuity, and nuclear cataract. If longitudinal studies confirm the association of refractive error with age, refractive surgery may achieve emmetropia only for a limited time.

Adult↗
PubMed2005

Enhanced salt tolerance mediated by AtHKT1 transporter-induced Na unloading from xylem vessels to xylem parenchyma cells.

AtHKT1 is a sodium (Na+) transporter that functions in mediating tolerance to salt stress. To investigate the membrane targeting of AtHKT1 and its expression at the translational level, antibodies were generated against peptides corresponding to the first pore of AtHKT1. Immunoelectron microscopy studies using anti-AtHKT1 antibodies demonstrate that AtHKT1 is targeted to the plasma membrane in xylem parenchyma cells in leaves. AtHKT1 expression in xylem parenchyma cells was also confirmed by AtHKT1 promoter-GUS reporter gene analyses. Interestingly, AtHKT1 disruption alleles caused large increases in the Na+ content of the xylem sap and conversely reduced the Na+ content of the phloem sap. The athkt1 mutant alleles had a smaller and inverse influence on the potassium (K+) content compared with the Na+ content of the xylem, suggesting that K+ transport may be indirectly affected. The expression of AtHKT1 was modulated not only by the concentrations of Na+ and K+ but also by the osmolality of non-ionic compounds. These findings show that AtHKT1 selectively unloads sodium directly from xylem vessels to xylem parenchyma cells. AtHKT1 mediates osmolality balance between xylem vessels and xylem parenchyma cells under saline conditions. Thus AtHKT1 reduces the sodium content in xylem vessels and leaves, thereby playing a central role in protecting plant leaves from salinity stress.

Arabidopsis↗
PubMed2005

Effect of glucose toxicity on intraportal tilapia islet xenotransplantation in nude mice.

BACKGROUND: Discordant xenogeneic islets transplanted intraportally into athymic nude rats experience primary non-function and are rapidly destroyed. Recently, it has been reported that adult porcine islets transplanted intraportally into nude mice are also rapidly destroyed and that this constitutes a new model for instant blood-mediated inflammatory reaction (IBMIR). METHODS: Tilapia (fish) islets were harvested, mechanically broken into mammalian islet-sized fragments, cultured for 48 h, and transplanted via the portal vein into athymic or euthymic mice. RESULTS: There were several groups of recipient mice. Streptozotocin-diabetic nude mice received 400 islets via the portal vein (n = 12). Recipients were killed when hyperglycemic (>200 mg/dl); livers and native pancreases were examined histologically. Mean graft survival time, based on function, was 5.4 +/- 1.2 days; at autopsy, histology showed occasional viable islets. We also performed a group of transplants in non-diabetic nude mice (n = 6) and then killed the recipients 2 or 4 weeks later; all had abundant viable, well-granulated islet grafts based on histology. Therefore, the intraportal environs in nude mice are not incompatible with discordant fish islets; rather, it appears as if hyperglycemia adversely affects the intraportal islet grafts (i.e. ''glucose toxicity''). To test this hypothesis, transplants were performed into non-diabetic nude mice and allowed to engraft for either 3 days (n = 6) or 10 days (n = 8) prior to injection of streptozotocin (200 to 220 mg/kg i.v.) to destroy the beta-cells in the recipients' native islets (n.b. tilapia islets are exceedingly resistant to streptozotocin); these recipients were followed for 28 days post-transplantation (or until hyperglycemic) and then killed for histology. Mean graft function exceeded 25 days for both groups and viable well-granulated, tilapia islets grafts were readily identified in all recipients; in all but one, the native pancreases were markedly beta-cell depleted -- confirming that normoglycemia was due to functional fish islet xenografts. CONCLUSIONS: Our results suggest that ''glucose toxicity'' plays a role in the immediate demise of intraportal tilapia islet xenografts.

Animals↗