bluuebunny/crossref_metadata_2025 huggingface dataset:
The Highly Conserved tRNA
His
Guanylyltransferase Thg1p Interacts with the Origin Recognition Complex and Is Required for the G
2
/M Phase Transition in the Yeast
Saccharomyces cerevisiae
Authors: Rice Terri S. , Ding Min , Pederson David S. , Heintz Nicholas H.
Published: April 2005

Here we show that the
Saccharomyces cerevisiae
tRNA
His
guanylyltransferase Thg1p interacts with the origin recognition complex in vivo and in vitro and that overexpression of hemagglutinin-Thg1p selectively impedes growth of
orc2
-
1
(Ts) cells at the permissive temperature. Studies with conditional mutants indicate that Thg1p couples nuclear division and migration to cell budding and cytokinesis in yeast.
BEAM DAMAGE OF CELLULAR SAMPLES IN IN-AIR MICRO PIXE ANALYSIS
Authors: KOMORI H. , MIZUMA K. , ISHII K. , YAMAZAKI H. , MATSUYAMA S. , AMARTAIVAN TS. , OHISHI Y. , RODRIGUEZ M. , YAMAGUCHI T. , SUZUKI A. , SATOH M. , KAMIYA T. , SAKAI T. , SATOH T. , OIKAWA M. , ARAKAWA K.
Published: April 2005

The change of shape and elemental concentration of cellular samples in In-Air micro PIXE analysis was investigated. Cultured bovine aortic endothelial cells were analyzed in the atmosphere by using 2.6 MeV proton micro-beams. The shape of cross-sections of cells was not so much distorted by beam irradiation and the concentrations of trace elements did not change too, except for S. The concentration of S changed with strongly depending on the temperature rise due to beam irradiation.
METHOD FOR DETERMINING THE LOCALIZATION OF TRACE ELEMENTS OBSERVED BY THE MICRO PIXE CAMERA
Authors: HARADA SATOSHI , ISHII K. , TANAKA A. , SATOH T. , MATSUYAMA S. , YAMAZAKI H. , KAMIYA T. , SAKAI T. , ARAKAWA K. , SAITOH M. , OIKAWA S. , SERA K.
Published: April 2005

The method to observe the localization of the trace elements in cultured human cell, by the micro Particle Induced X-ray Emission (PIXE) camera, was developed.

The analyzed samples received the eosin staining, which colored the nucleus of cell violet. The scanned areas of the sample with particle irradiation were colored brown by the heat during irradiation. The brown scanned areas were examined by an optical microscope at 400 X magnification and photographed. Then the photo was digitized and loaded into the microcomputer. By microcomputer, the photo of the scanned area was superimposed onto the image of the micro PIXE camera, by matching the scanned area to the image of micro PIXE camera.

This superimposed image enabled us to determine whether the elements exists in cytosol, or in nucleus.
PRELIMINARY STUDY OF RIVER WATER IN GOLD MINING AREAS OF CAMBODIA
Authors: MURAO SATOSHI , NISHIYAMA FUMITAKA , SIENG SOTHAM
Published: April 2005

In Cambodia, artisanal mining has recently come to a social concern because of the possibility to cause environmental degradation and human health problems. The General Department of Mineral Resources of Cambodia is collecting environmental specimens in mining sites to watch the situation. This time, four water samples from Sampov Loon and one from Memong mining site were sent from the Department to Hiroshima University, Japan, and the samples were analyzed by means of PIXE at the University. A volume of 10 μl from each sample was separated and dropped onto 4 μm polypropylene backing foil. The measurement was carried out by using 2.5 MV single-ended Van de Graaff accelerator. A Si(Li) detector (active area, 80mm2; sensitive depth, 5mm; Be -window's thickness, 25 μm; resolution, 167 eV fwhm at 5.9 keV) was used for both of in vacuo PIXE and non-vacuum external beam PIXE measurement. A computer code PIXS was used for the quantification. The result indicates that there are at least two kinds of water in Sampov Loon and one of them possibly represents polluted condition.
SOURCE APPORTIONMENT OF FINE AIRBORNE PARTICULATE MATTER COLLECTED IN THE MEXICO CITY METROPOLITAN AREA
Authors: ALDAPE F. , FLORES M. J.
Published: April 2005

Samples of fine airborne particulate matter ( PM 2.0) have been collected at three sites located in the Mexico City Metropolitan Area (MCMA) during July, August, and September 2000. The elemental concentrations of these samples were determined by PIXE so that twelve elements ( S , Cl , K , Ca , Ti , Mn , Fe , Ni , Cu , Zn , Br and Pb ) were consistently detected. These results produced a database, which was statistically analysed; first by Principal Components so to identify the pollution sources, and, subsequently, by Absolute Principal Component Scores analysis in order to estimate the corresponding source apportionment contributions. Other elements such as V and Cr were also detected in around 20% of the samples and, therefore, they were not considered statistically significant. Thus, these elements, as well as some others found only occasionally and in the trace range, were left out of the discussion. All calculations were performed using a standard statistical package following the method developed by Thurston and Spengler. Four main pollution sources were identified and the source apportionments were found in good agreement with other estimations found in the literature. The results were obtained individually for the three sampling sites, but the complete results are presented for just one of the sites in order to simplify this presentation.
REAL SURFACES IN ELLIPTIC SURFACES
Authors: SLAPAR MARKO
Published: April 2005

We study the structure of complex points on real surfaces, embedded into complex elliptic surfaces. We show, for example, that any compact connected surface has a totally real embedding into a blow-up of a K3 surface. We also exhibit smooth disc bundles over compact connected orientable surfaces that have a Stein structure as Stein domains inside elliptic surfaces.
BIRATIONAL EQUIVALENCE OF HIGGS MODULI
Authors: MEHTA MRIDUL
Published: April 2005

In this paper, we study triples of the form (E, θ, ϕ) over a compact Riemann surface, where (E, θ) is a Higgs bundle and ϕ is a global holomorphic section of the Higgs bundle. Our main result is an description of a birational equivalence which relates geometrically the moduli space of Higgs bundles of rank r and degree d to the moduli space of Higgs bundles of rank r-1 and degree d.
LOCAL L2 RESULTS FOR $\bar\partial$: THE ISOLATED SINGULARITIES CASE
Authors: FORNÆSS JOHN ERIK , ØVRELID NILS , VASSILIADOU SOPHIA
Published: April 2005

Let X be a reduced pure n-dimensional complex analytic set in ℂN with an isolated singularity at 0. We obtain some L2-existence and regularity results for the [Formula: see text]-operator on a deleted neighborhood of the singular point 0 in X.
Biophysical evidence that connexin-36 forms functional gap junction channels between pancreatic mouse β-cells
Authors: Moreno Alonso P. , Berthoud Viviana M. , Pérez-Palacios Gregorio , Pérez-Armendariz E. Martha
Published: April 2005

Connexin-36 (Cx36) is the only gap junction protein that has been unambiguously identified in rodent pancreatic β-cells. However, properties of gap junction channel unitary currents between β-cells remain unrevealed. To address whether Cx36 forms functional channels in β-cells, we characterized biophysical properties of macro- and microscopic junctional currents recorded from dual whole cell voltage clamp isolated pairs of dispersed mouse β-cells. Electrical coupling was recorded in 80% of cell pairs with a junctional conductance ( gj) of 355 ± 45 pS ( n = 20). Transjunctional voltage dependence was identified in three of seven cell pairs with high-input membrane resistances. Normalized steady-state gj ( Gj) and transjunctional-voltage relation were well described by a two-state Boltzmann equation [maximal conductance ( Gmax) = 1.0, voltage-insensitive conductance ( Gmin) = 0.3 and 0.28, voltage gating sensitivity ( A) = 0.21 and 0.23, and voltage at which one-half of the initial voltage-dependent conductance was reached ( Vo) = −85 and 87 mV for negative and positive potentials, respectively]. Halothane reversibly uncoupled β-cell pairs, and, during recovery, unitary conductances of 5–10 pS were recorded while using patch pipettes containing mainly CsCl. Although these properties are similar to those previously described for Cx36 channels in mammalian cell systems, we found that β-cell junctional currents were insensitive to quinine. Cx36 transcript and protein expression in islets and freshly dispersed cell preparations was confirmed by RT-PCR and immunofluorescence. In conclusion, biophysical properties of junctional channels between β-cells are similar but not identical to those previously described for homomeric Cx36 channels. Cell type-specific mechanisms that may account for these differences are discussed.
GLUT4 expression and subcellular localization in the intrauterine growth-restricted adult rat female offspring
Authors: Thamotharan Manikkavasagar , Shin Bo-Chul , Suddirikku Dilika T. , Thamotharan Shanthie , Garg Meena , Devaskar Sherin U.
Published: April 2005

Intrauterine growth restriction (IUGR) leads to obesity, glucose intolerance, and type 2 diabetes mellitus in the adult. To determine the mechanism(s) behind this “metabolic imprinting” phenomenon, we examined the effect of total calorie restriction during mid- to late gestation modified by postnatal ad libitum access to nutrients (CM/SP) or nutrient restriction (SM/SP) vs. postnatal nutrient restriction alone (SM/CP) on skeletal muscle and white adipose tissue (WAT) insulin-responsive glucose transporter isoform (GLUT4) expression and insulin-responsive translocation. A decline in skeletal muscle GLUT4 expression and protein concentrations was noted only in the SM/SP and SM/CP groups. In contrast, WAT demonstrated no change in GLUT4 expression and protein concentrations in all experimental groups. The altered in utero hormonal/metabolic milieu was associated with a compensatory adaptation that persisted in the adult and consisted of an increase in the skeletal muscle basal plasma membrane-associated GLUT4 concentrations. This perturbation led to no further exogenous insulin-induced GLUT4 translocation, thereby disabling the insulin responsiveness of the skeletal muscle but retaining it in WAT. These changes, which present at birth, collectively maximize basal glucose transport to the compromised skeletal muscle with a relative resistance to exogenous/postprandial insulin. Preservation of insulin responsiveness in WAT may serve as a sink that absorbs postprandial nutrients that can no longer efficiently access skeletal muscle. We speculate that, in utero, GLUT4 aberrations may predict type 2 diabetes mellitus, whereas postnatal nutrient intake may predict obesity, thereby explaining the heterogeneous phenotype of the IUGR adult offspring.
The p55 TNF receptor mediates TNF inhibition of osteoblast differentiation independently of apoptosis
Authors: Gilbert Linda C. , Rubin Janet , Nanes Mark S.
Published: April 2005

After menopause, increased tumor necrosis factor-α (TNF-α) stimulates bone resorption while inhibiting differentiation of new bone-forming osteoblasts (OB). TNF receptors, p55 and p75, signal similar intracellular pathways, but only p55 activates apoptosis. To evaluate the relationship between the TNF receptor mediating inhibition of OB differentiation and the role of apoptosis, marrow stromal cells (MSC) were cultured from mice deficient in either or both receptors. Cells grown in ascorbate and β-glycerophosphate produce alkaline phosphatase and osteocalcin and mineralize matrix. Treatment of wild-type or p55+/+/p75−/−MSC with murine TNF (binds p55 and p75) or human TNF (binds only p55) inhibited OB differentiation. TNF did not inhibit OB differentiation in p55−/−MSC. Expression of p75 modestly attenuated sensitivity to TNF. To determine the role of apoptosis, changes in total DNA, cell viability, caspase 3, and percentage of annexin V-positive cells were measured in MSC and preosteoblastic MC3T3 cells. TNF treatment that reduced differentiation by 50% did not decrease cell viability or increase apoptosis, as determined by alamar blue reduction, trypan blue exclusion, and percentage of annexin V-positive cells. TNF increased caspase 3 activity 1.5-fold in MC3T3 and insignificantly in MSC cells compared with >4-fold after 4 h actinomycin D. Treatment of MSC or MC3T3 cells with three caspase inhibitors failed to reverse the inhibitory effect of TNF on OB differentiation despite inhibition of caspase activity. These results suggest that the p55 receptor is essential, and p75 dispensable, for TNF inhibition of OB differentiation through a mechanism that does not require apoptosis.
A 5-HT4agonist, mosapride, enhances intrinsic rectorectal and rectoanal reflexes after removal of extrinsic nerves in guinea pigs
Authors: Kojima Yu , Nakagawa Tadashi , Katsui Renta , Fujii Hisao , Nakajima Yoshiyuki , Takaki Miyako
Published: April 2005

Distension-evoked reflex of rectorectal (R-R) contractions and rectointernal anal sphincter (R-IAS) relaxations can be generated in guinea pigs through an extrinsic sacral excitatory neural pathway (pelvic nerves) as well as intrinsic cholinergic excitatory and nitrergic inhibitory pathways. The aim of the present study was to create intrinsic R-R and R-IAS reflex models by pithing (destruction of the lumbar and sacral cords; PITH) and to evaluate whether the prokinetic benzamide mosapride, a 5-HT4receptor agonist, enhances these reflexes. The mechanical activities of the R-R and R-IAS were recorded in the anesthetized guinea pig on days 2–9 after PITH. Although the basal rectal pressure at distension after PITH was significantly lower than control, the reflex indexes of R-R contractions and synchronous R-IAS relaxations were unchanged between days 4 and 9 after PITH. The frequency of spontaneous rectal and IAS motility were also unchanged. Immunohistochemical studies revealed that the distribution of myenteric and intramuscular interstitial cells of Cajal (ICC) were not altered after PITH. Mosapride (0.1–1.0 mg/kg iv) dose-dependently increased both intrinsic R-R (maximum: 1.82) and R-IAS reflex indexes (maximum: 2.76) from control (1.0) 6–9 days after PITH. The 5-HT4receptor antagonist, GR-113808 (1.0 mg/kg iv) decreased the R-R and R-IAS reflex indexes by ∼50% and antagonized the effect of mosapride (1.0 mg/kg iv). The present results indicate that mosapride moderately enhanced intrinsic R-R and R-IAS reflexes functionally compensated after deprivation of extrinsic nerves, mediated through endogenously active intrinsic 5-HT4receptors.
CD38/cyclic ADP-ribose signaling: role in the regulation of calcium homeostasis in airway smooth muscle
Authors: Deshpande Deepak A. , White Thomas A. , Dogan Soner , Walseth Timothy F. , Panettieri Reynold A. , Kannan Mathur S.
Published: April 2005

The contractility of airway smooth muscle cells is dependent on dynamic changes in the concentration of intracellular calcium. Signaling molecules such as inositol 1,4,5-trisphosphate and cyclic ADP-ribose play pivotal roles in the control of intracellular calcium concentration. Alterations in the processes involved in the regulation of intracellular calcium concentration contribute to the pathogenesis of airway diseases such as asthma. Recent studies have identified cyclic ADP-ribose as a calcium-mobilizing second messenger in airway smooth muscle cells, and modulation of the pathway involved in its metabolism results in altered calcium homeostasis and may contribute to airway hyperresponsiveness. In this review, we describe the basic mechanisms underlying the dynamics of calcium regulation and the role of CD38/cADPR, a novel pathway, in the context of airway smooth muscle function and its contribution to airway diseases such as asthma.
Inhibition of 20-HETE abolishes the myogenic response during NOS antagonism in the ovine fetal pulmonary circulation
Authors: Parker Thomas A. , Grover Theresa R. , Kinsella John P. , Falck John R. , Abman Steven H.
Published: April 2005

Mechanisms that maintain high pulmonary vascular resistance (PVR) and oppose vasodilation in the fetal lung are poorly understood. In fetal lambs, increased pulmonary artery pressure evokes a potent vasoconstriction, suggesting that a myogenic response contributes to high PVR in the fetus. In adult systemic circulations, the arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) has been shown to modulate the myogenic response, but its role in the fetal lung is unknown. We hypothesized that acute increases in pulmonary artery pressure release 20-HETE, which causes vasoconstriction, or a myogenic response, in the fetal lung. To address this hypothesis, we studied the hemodynamic effects of N-methylsufonyl-12,12-dibromododec-11-enamide (DDMS), a specific inhibitor of 20-HETE production, on the pulmonary vasoconstriction caused by acute compression of the ductus arteriosus (DA) in chronically prepared fetal sheep. An inflatable vascular occluder around the DA was used to increase pulmonary artery pressure under three study conditions: control, after pretreatment with nitro-l-arginine (l-NA; to inhibit shear-stress vasodilation), and after combined treatment with both l-NA and a specific 20-HETE inhibitor, DDMS. We found that DA compression after l-NA treatment increased PVR by 44 ± 12%. Although intrapulmonary DDMS infusion did not affect basal PVR, DDMS completely abolished the vasoconstrictor response to DA compression in the presence of l-NA (44 ± 12% vs. 2 ± 4% change in PVR, l-NA vs. l-NA + DDMS, P < 0.05). We conclude that 20-HETE mediates the myogenic response in the fetal pulmonary circulation and speculate that pharmacological inhibition of 20-HETE might have a therapeutic role in neonatal conditions characterized by pulmonary hypertension.
Cyclic stretch increases VEGF expression in pulmonary arterial smooth muscle cells via TGF-β1 and reactive oxygen species: a requirement for NAD(P)H oxidase
Authors: Mata-Greenwood Eugenia , Grobe Albert , Kumar Sanjiv , Noskina Yelina , Black Stephen M.
Published: April 2005

Our previous studies have indicated that transforming growth factor (TGF)-β1 and VEGF expression are increased in the smooth muscle cell (SMC) layer of the pulmonary vessels of lambs with pulmonary hypertension secondary to increased pulmonary blood flow. Furthermore, we found that TGF-β1 expression increased before VEGF. Because of the increased blood flow in the shunt lambs, the SMC in the pulmonary vessels are exposed to increased levels of the mechanical force, cyclic stretch. Thus, in this study, using primary cultures of pulmonary arterial SMC isolated from pulmonary arteries of 4-wk-old lambs, we investigated the role of cyclic stretch in the apparent coordinated regulation of TGF-β1 and VEGF. Our results demonstrated that cyclic stretch induced a significant increase in VEGF expression both at the mRNA and protein levels ( P < 0.05). The increased VEGF mRNA was preceded by both an increased expression and secretion of TGF-β1 and an increase in reactive oxygen species (ROS) generation. In addition, a neutralizing antibody against TGF-β1 abolished the cyclic stretch-dependent increases in both superoxide generation and VEGF expression. Our data also demonstrated that cyclic stretch activated an NAD(P)H oxidase that was TGF-β1 dependent and that NAD(P)H oxidase inhibitors abolished the cyclic stretch-dependent increase in VEGF expression. Therefore, our results indicate that cyclic stretch upregulates VEGF expression via the TGF-β1-dependent activation of NAD(P)H oxidase and increased generation of ROS.
Ghrelin is an orexigenic and metabolic signaling peptide in the arcuate and paraventricular nuclei
Authors: Currie Paul J. , Mirza Aaisha , Fuld Rebecca , Park Diana , Vasselli Joseph R.
Published: April 2005

Ghrelin is a 28-amino acid acylated peptide and is the endogenous ligand for the growth hormone secretagogue receptor (GHS-R). The GHS-R is expressed in hypothalamic nuclei, including the arcuate nucleus (Arc) where it is colocalized with neuropeptide Y (NPY) neurons. In the present study, we examined the effects of ghrelin on feeding and energy substrate utilization (respiratory quotient; RQ) following direct injections into either the arcuate or the paraventricular nucleus (PVN) of the hypothalamus. Ghrelin was administered at the beginning of the dark cycle at doses of 15–60 pmol to male and female rats. In feeding studies, food intake was measured 2 and 4 h postinjection. Separate groups of rats were injected with ghrelin, and the RQ (V̇co2/V̇o2) was measured using an open circuit calorimeter over a 4-h period. Both Arc and PVN injections of ghrelin increased food intake in male and female rats. Ghrelin also increased RQ, reflecting a shift in energy substrate utilization in favor of carbohydrate oxidation. Because these effects are similar to those observed after PVN injection of NPY, we then assessed the impact of coinjecting ghrelin with NPY into the PVN. When rats were pretreated with very low doses of ghrelin (2.5–10 pmol), NPY's (50 pmol) effects on eating and RQ were potentiated. Overall, these data are in agreement with evidence suggesting that ghrelin functions as a gut-brain endocrine hormone implicated in the regulation of food intake and energy metabolism. Our findings are also consistent with a possible interactive role of hypothalamic ghrelin and NPY systems.
Bidirectional regulation of AQP2 trafficking and recycling: involvement of AQP2-S256 phosphorylation
Authors: Nejsum Lene N. , Zelenina Marina , Aperia Anita , Frøkiær Jørgen , Nielsen Søren
Published: April 2005

The present study examined the role of PKA and serine256 (S256) phosphorylation for AQP2 trafficking and recycling using cells transfected with wild-type AQP2 (AQP2-WT) or mutant AQP2 and high-resolution confocal microscopic techniques. In transiently transfected MDCK-C7 cells, stimulation with forskolin induced translocation of AQP2-WT to the plasma membrane. Treatment of AQP2-WT cells with the PKA inhibitor H-89 following forskolin stimulation resulted in internalization of AQP2-WT. Moreover, H-89 treatment of AQP2-S256D (mimicking constitutively phosphorylated AQP2 and hence localized to the plasma membrane) resulted in redistribution of AQP2-S256D to intracellular vesicles, even in the presence of forskolin. Both PGE2and dopamine stimulation induced endocytosis of AQP2-WT and AQP2-S256D, respectively, in forskolin-stimulated cells. Consistent with this, dopamine in the presence of vasopressin stimulated endocytosis of AQP2 in slices of rat kidney inner medulla without substantial dephosphorylation. In conclusion, these results strongly suggest that 1) S256 phosphorylation is necessary but not sufficient for AQP2 plasma membrane expression, 2) active PKA is required for AQP2 plasma membrane expression, 3) PGE2and dopamine induce internalization of AQP2 independently of AQP2 dephosphorylation, and 4) preceding activation of cAMP production is necessary for PGE2and dopamine to cause AQP2 internalization.
Endothelial cell dysfunction: can’t live with it, how to live without it
Authors: Goligorsky Michael S.
Published: April 2005

Endothelial cell dysfunction is emerging as an ultimate culprit for diverse cardiovascular diseases and cardiovascular complications of chronic renal diseases, yet the definition of this new syndrome, its pathophysiology, and therapy remain poorly defined. Here, I summarize some molecular mechanisms leading from hyperhomocystinemia, elevated asymmetric dimethylarginine, and advanced glycolation end product-modified protein level to the proatherogenic, prothrombogenic, and proinflammatory endothelial phenotype and offer a model of endothelial dysfunction based on the interconnectedness of diverse functions. Finally, several therapeutic strategies to prevent and correct endothelial dysfunction are discussed in the light of uncertainty of their action modulated by the endothelial dysfunction per se.
Superoxide enhances Na-K-2Cl cotransporter activity in the thick ascending limb
Authors: Juncos Ramiro , Garvin Jeffrey L.
Published: April 2005

Superoxide (O2−) enhances Na reabsorption by the thick ascending limb (THAL). Na absorption in this segment involves the Na-K-2Cl cotransporter, K channel, and Na-K-ATPase. We hypothesized that O2−stimulates NaCl absorption primarily by enhancing Na-K-2Cl cotransport. First, we measured steady-state intracellular Na (Nai) and chloride (Cli). Xanthine oxidase (XO; 0.75 mU/ml) and hypoxanthine (HX; 0.125 mM) were added to the bath to increase O2−. During the control period, Naiwas 12.2 ± 1.9 mM. After treatment with O2−, it rose to 20.9 ± 3.3 mM, a 71% increase ( P < 0.01). Clialso increased ( P < 0.01). Neither XO nor HX alone had a significant effect on Naior Cli. Next, we tested cotransport activity by measuring the initial rate of increase in Naicaused by changing luminal Na-Cl-K from 50/0/0 to 140/134/4 mM. During the control period, the initial rate of increase was 0.13 ± 0.02 arbitrary units (AU)/min. After treatment with O2−, it was 0.22 ± 0.04 AU/min ( P < 0.025), a 69% increase. Neither XO nor HX alone had a significant effect. Furosemide completely blocked the increase in intracellular Na in the control and O2−treatment periods. Next, we studied K channel activity by measuring the depolarization caused by increasing luminal K from 1 to 25 mM using a voltage-sensitive dye. During the control period, maximum depolarization was 7.31 ± 0.77 AU. After O2−treatment, it was 6.18 ± 0.90 AU ( P < 0.05), a 15% decrease. Finally, we assessed the effects of O2−on Na-K-ATPase activity in THAL suspensions by measuring ATP hydrolysis. Vmaxand K1/2for Na were not affected by O2−. We concluded that O2−stimulates THAL NaCl absorption primarily by enhancing Na entry via Na-K-2Cl cotransport.
Urea and urine concentrating ability: new insights from studies in mice
Authors: Yang Baoxue , Bankir Lise
Published: April 2005

Urea is the most abundant solute in the urine in humans (on a Western-type diet) and laboratory rodents. It is far more concentrated in the urine than in plasma and extracellular fluids. This concentration depends on the accumulation of urea in the renal medulla, permitted by an intrarenal recycling of urea among collecting ducts, vasa recta and thin descending limbs, all equipped with specialized, facilitated urea transporters (UTs) (UT-A1 and 3, UT-B, and UT-A2, respectively). UT-B null mice have been recently generated by targeted gene deletion. This review describes 1) the renal handling of urea by the mammalian kidney; 2) the consequences of UT-B deletion on urinary concentrating ability; and 3) species differences among mice, rats, and humans related to their very different body size and metabolic rate, leading to considerably larger needs to excrete and to concentrate urea in smaller species (urea excretion per unit body weight in mice is 5 times that in rats and 23 times that in humans). UT-B null mice have a normal glomerular filtration rate but moderately reduced urea clearance. They exhibit a 30% reduction in urine concentrating ability with a more severe defect in the capacity to concentrate urea (50%) than other solutes, despite a twofold enhanced expression of UT-A2. The urea content of the medulla is reduced by half, whereas that of chloride is almost normal. When given an acute urea load, UT-B null mice are unable to raise their urinary osmolality, urine urea concentration (Uurea), and the concentration of non-urea solutes, as do wild-type mice. When fed diets with progressively increasing protein content (10, 20, and 40%), they cannot prevent a much larger increase in plasma urea than wild-type mice because they cannot raise Uurea. In both wild-type and UT-B null mice, urea clearance was higher than creatinine clearance, suggesting the possibility that urea could be secreted in the mouse kidney, thus allowing more efficient excretion of the disproportionately high urea load. On the whole, studies in UT-B null mice suggest that recycling of urea by countercurrent exchange in medullary vessels plays a more crucial role in the overall capacity to concentrate urine than its recycling in the loops of Henle.
Segmental expression of Notch and Hairy genes in nephrogenesis
Authors: Chen Linghong , Al-Awqati Qais
Published: April 2005

Notch signaling pathway genes are required for nephrogenesis, raising the possibility that Notch effector Hairy-related genes should also control nephron formation. We performed in situ hybridization of Hairy transcription factors with segment-specific lectins and/or antibodies during early nephrogenesis to identify their possible roles in segment identity of the nephron. We found that among all of Notch downstream Hairy genes, only Hes1, Hes5, Hey1, and HeyL were expressed in a segment-specific manner in early nephrons and their expression pattern changed dynamically during metanephric development. Based on these patterns of expression, it was possible to propose a pairwise association of specific ligand and receptor and to suggest that the effector of this association is one of the Hairy transcription factors. We found that Hes5 is specifically expressed in the anlage of the loop of Henle, suggesting that it might be involved in the determination of its cell identity. We also examined the morphological appearance of kidneys from mice where the Hes1 or Hes5 genes were deleted and found that at least at the gross morphological level, there was little difference from wild-type kidneys. Because Hairy genes associate with other transcription factors to exert their effect, it is necessary to examine a more complete array of genetic deletions before a conclusion can be reached regarding their role in kidney development. These studies provide the basis for the future development of strategies to examine the role of individual effector molecules in the determination of the differentiation pattern of the nephron.
Acute renal failure in zebrafish: a novel system to study a complex disease
Authors: Hentschel Dirk M. , Park Kwon Moo , Cilenti Lucia , Zervos Antonis S. , Drummond Iain , Bonventre Joseph V.
Published: April 2005

Acute renal failure (ARF) is characterized by a very high mortality essentially unchanged over the past 40 years. Simple vertebrate models are needed to improve our understanding of ARF and facilitate the development of novel therapies for this clinical syndrome. Here, we demonstrate that gentamicin, a commonly used nephrotoxic antibiotic, causes larval zebrafish to develop ARF characterized by histological and functional changes that mirror aminoglycoside toxicity in higher vertebrates and inability of zebrafish to maintain fluid homeostasis. We developed a novel method to quantitate renal function in larval zebrafish and demonstrate a decline in glomerular filtration rate after gentamicin exposure. The antineoplastic drug cisplatin, whose use in humans is limited by kidney toxicity, also causes typical histological changes and a decline in renal function in larval zebrafish. A specific inhibitor of Omi/HtrA2, a serine protease implicated in cisplatin-induced apoptosis, prevented renal failure and increased survival. This protective effect was confirmed in a mouse model of cisplatin-induced nephrotoxicity. Therefore, zebrafish provides a unique model system, amenable to genetic manipulation and drug screening, to explore the pathophysiology of ARF and establish novel therapies with potential use in mammals.
ACTN3 and MLCK genotype associations with exertional muscle damage
Authors: Clarkson Priscilla M. , Hoffman Eric P. , Zambraski Edward , Gordish-Dressman Heather , Kearns Amy , Hubal Monica , Harmon Brennan , Devaney Joseph M.
Published: April 2005

Strenuous exercise results in damage to skeletal muscle that is manifested in delayed muscle pain, prolonged strength loss, and increases in muscle proteins in the blood, especially creatine kinase (CK) and myoglobin (Mb). Some individuals experience profound changes in these variables in response to standard laboratory exercise or recreational activities. We proposed that variations in genes coding for two myofibrillar proteins [α-actinin 3 (ACTN3) and myosin light chain kinase (MLCK)] may explain the large variability in the response to muscle-damaging exercise. We hypothesized that subjects with specific single nucleotide polymorphisms (SNPs) in ACTN3 and MLCK would show a greater loss in muscle strength and/or a greater increase in blood CK and Mb in response to eccentric exercise. Blood from 157 subjects who performed a standard elbow flexion eccentric exercise protocol was tested for association between genotypes of ACTN3 (1 SNP tested: R577X) and MLCK (2 SNPs tested: C49T and C37885A) and changes in blood CK and Mb and isometric strength. Subjects possessing the ACTN3-deficient genotype (XX) had lower baseline CK compared with the heterozygotes ( P = 0.035). After the eccentric exercise, those subjects homozygous for the MLCK 49T rare allele had a significantly greater increase in CK and Mb ( P < 0.01) compared with the heterozygotes, and those heterozygous for MLCK C37885A had a significantly greater increase in CK compared with the homozygous wild type ( P < 0.05). There was only one subject homozygous for the rare MLCK 37885A allele. MLCK C37885A was also associated with postexercise strength loss ( P < 0.05); the heterozygotes demonstrated greater strength loss compared with the homozygous wild type (CC). These results show that variations in genes coding for specific myofibrillar proteins influence phenotypic responses to muscle damaging exercise.
Glycerol hyperhydration: physiological responses during cold-air exposure
Authors: O'Brien Catherine , Freund Beau J. , Young Andrew J. , Sawka Michael N.
Published: April 2005

Hypohydration occurs during cold-air exposure (CAE) through combined effects of reduced fluid intake and increased fluid losses. Because hypohydration is associated with reduced physical performance, strategies for maintaining hydration during CAE are important. Glycerol ingestion (GI) can induce hyperhydration in hot and temperate environments, resulting in greater fluid retention compared with water (WI) alone, but it is not effective during cold-water immersion. Water immersion induces a greater natriuresis and diuresis than cold exposure; therefore, whether GI might be effective for hyperhydration during CAE remains unknown. This study examined physiological responses, i.e., thermoregulatory, cardiovascular, renal, vascular fluid, and fluid-regulating hormonal responses, to GI in seven men during 4 h CAE (15°C, 30% relative humidity). Subjects completed three separate, double-blind, and counterbalanced trials including WI (37 ml water/l total body water), GI (37 ml water/l total body water plus 1.5 g glycerol/l total body water), and no fluid. Fluids were ingested 30 min before CAE. Thermoregulatory responses to cold were similar during each trial. Urine flow rates were higher ( P = 0.0001) with WI (peak 11.8 ml/min, SD 1.9) than GI (5.0 ml/min, SD 1.8), and fluid retention was greater ( P = 0.0001) with GI (34%, SD 7) than WI (18%, SD 5) at the end of CAE. Differences in urine flow rate and fluid retention were the result of a greater free water clearance with WI. These data indicate glycerol can be an effective hyperhydrating agent during CAE.
Long-term electromyographic activity in upper trapezius and low back muscles of women with moderate physical activity
Authors: Mork Paul Jarle , Westgaard Rolf H.
Published: April 2005

The habitual activity patterns of trapezius and postural back muscles (multifidus, iliocostalis, longissimus) of 23 female subjects with moderate physical activity were studied. Bilateral surface electromyographic (sEMG) recordings from start of work until bedtime were analyzed. The activity level was calibrated as percentage of root mean square-detected muscle activity at maximal voluntary contraction (EMGmax). Sixty-six previous trapezius recordings of women with moderate physical activity were included in some analyses to pursue the full range of variation in trapezius activity. Twenty-six of these were recorded twice, separated by 16–28 mo. Median activity level and duration of periods with sEMG activity of <0.5% EMGmax(“rest time”; only trapezius) and exceeding 2 (“burst time”), 10, 30, and 50% EMGmaxwas determined. The trapezius median activity level ranged from 0.6 to 8.8% EMGmax, burst time from 9 to 84%, and rest time from 2 to 84%. The activity patterns of the back muscles showed similar large interindividual variation. Repeated trapezius recordings of the same subject showed high consistency; intraclass correlation coefficients ranged from 0.62 to 0.79 for different sEMG variables. Periods with high sEMG amplitude were of short duration; 7% of the trapezius recordings did not present time intervals (0.2-s duration) above 50% EMGmax. The activity patterns of the postural muscles, despite large interindividual variability, were distinctly different from activity patterns of upper and lower limb muscles reported by others (e.g., mean burst time 40–50 vs. 10–20%). We conclude that postural trunk muscles show idiosyncratic activity patterns with large interindividual variation. High-threshold motor units are activated to a very minor extent.
Mechanical stimulation of the plantar foot surface attenuates soleus muscle atrophy induced by hindlimb unloading in rats
Authors: Kyparos Antonios , Feeback Daniel L. , Layne Charles S. , Martinez Daniel A. , Clarke Mark S. F.
Published: April 2005

Unloading-induced muscle atrophy occurs in the aging population, bed-ridden patients, and astronauts. This study was designed to determine whether dynamic foot stimulation (DFS) applied to the plantar surface of the rat foot can serve as a countermeasure to soleus muscle atrophy normally observed in hindlimb unloaded (HU) rats. Forty-four mature (6 mo old), male Wistar rats were randomly assigned to ambulatory control, HU alone, HU with active DFS (i.e., plantar contact with active inflation), HU with passive DFS (i.e., plantar contact without active inflation), and HU while wearing a DFS boot with no plantar contact groups. Application of active DFS during HU significantly counteracted the atrophic response by preventing ∼85% of the reduction in type I myofiber cross-sectional area (CSA) in the soleus while preventing ∼57% of the reduction in type I myofiber CSA and 43% of the reduction in type IIA myofiber CSA of the medial gastrocnemius muscle. Wearing of a DFS boot without active inflation prevented myofiber atrophy in the soleus of HU animals in a fashion similar to that observed in HU animals that wore an actively inflated DFS boot. However, when a DFS boot without plantar surface contact was worn during HU, no significant protection from HU-induced myofiber atrophy was observed. These results illustrate that the application of mechanical foot stimulation to the plantar surface of the rat foot is an effective countermeasure to muscle atrophy induced by HU.
Tyrosine hydroxylase expression and activity in the rat brain: differential regulation after long-term intermittent or sustained hypoxia
Authors: Gozal Evelyne , Shah Zahoor A. , Pequignot Jean-Marc , Pequignot Jacqueline , Sachleben Leroy R. , Czyzyk-Krzeska Maria F. , Li Richard C. , Guo Shang-Z. , Gozal David
Published: April 2005

Tyrosine hydroxylase, a hypoxia-regulated gene, may be involved in tissue adaptation to hypoxia. Intermittent hypoxia, a characteristic feature of sleep apnea, leads to significant memory deficits, as well as to cortex and hippocampal apoptosis that are absent after sustained hypoxia. To examine the hypothesis that sustained and intermittent hypoxia induce different catecholaminergic responses, changes in tyrosine hydroxylase mRNA, protein expression, and activity were compared in various brain regions of male rats exposed for 6 h, 1 day, 3 days, and 7 days to sustained hypoxia (10% O2), intermittent hypoxia (alternating room air and 10% O2), or normoxia. Tyrosine hydroxylase activity, measured at 7 days, increased in the cortex as follows: sustained > intermittent > normoxia. Furthermore, activity decreased in the brain stem and was unchanged in other brain regions of sustained hypoxia-exposed rats, as well as in all regions from animals exposed to intermittent hypoxia, suggesting stimulus-specific and heterotopic catecholamine regulation. In the cortex, tyrosine hydroxylase mRNA expression was increased, whereas protein expression remained unchanged. In addition, significant differences in the time course of cortical Ser40tyrosine hydroxylase phosphorylation were present in the cortex, suggesting that intermittent and sustained hypoxia-induced enzymatic activity differences are related to different phosphorylation patterns. We conclude that long-term hypoxia induces site-specific changes in tyrosine hydroxylase activity and that intermittent hypoxia elicits reduced tyrosine hydroxylase recruitment and phosphorylation compared with sustained hypoxia. Such changes may not only account for differences in enzyme activity but also suggest that, with differential regional brain susceptibility to hypoxia, recruitment of different mechanisms in response to hypoxia will elicit region-specific modulation of catecholamine response.
Peptidergic Contribution to Posttetanic Potentiation at a Central Synapse of Aplysia
Authors: Koh Hae-Young , Weiss Klaudiusz R.
Published: April 2005

Posttetanic potentiation (PTP)-like phenomena appear to be mediated by a variety of mechanisms. Although neuropeptides are located in a large number of neurons and many neuropeptides, like PTP, can enhance synaptic transmission, there is a paucity of studies indicating that peptides may actually participate in PTP. Here, we utilize a single central synapse in the feeding circuit of Aplysia to investigate a possible peptidergic contribution to PTP in the CNS. The cholinergic command-like interneuron, cerebral-buccal interneuron 2 (CBI-2), contains two neuropeptides, feeding circuit activating peptide (FCAP) and cerebral peptide 2 (CP2). Previous studies showed that tetanic prestimulation or repeated stimulation of CBI-2, as well as perfusion of FCAP and CP2, increase the size of the cholinergic excitatory postsynaptic potentials (EPSPs) that CBI-2 evokes in the motoneurons B61/62 and shorten the latency to initiate B61/62 firing in response to CBI-2 stimulation. We used temperature-dependent suppression of peptide release and occlusion experiments to examine the possible contribution of FCAP and CP2 to PTP at the CBI-2 to B61/62 synapse. When peptide release was suppressed, perfusion of exogenous peptides increased the size of posttetanic EPSPs. In contrast, when peptide release was not suppressed, exogenous peptides did not enhance the size of posttetanic EPSPs, thus indicating occlusion. Temperature manipulation and occlusion experiments also indicated that peptides extend PTP duration. This peptide-dependent prolongation of PTP has functional consequences in that it extends the duration of time during which the latency to initiate B61/62 firing in response to CBI-2 stimulation is shortened.
Powerful, Onset Inhibition in the Ventral Nucleus of the Lateral Lemniscus
Authors: Nayagam David A. X. , Clarey Janine C. , Paolini Antonio G.
Published: April 2005

The function of the ventral nucleus of the lateral lemniscus (VNLL), a secondary processing site within the auditory brain stem, is unclear. It is known to be a major source of inhibition to the inferior colliculus (IC). It is also thought to play a role in coding the temporal aspects of sound, such as onsets and the periodic components of complex stimuli. In vivo intracellular recordings from VNLL neurons ( n = 56) in urethane anesthetized rats revealed the presence of large-amplitude, short-duration, onset inhibition in a subset of neurons (14.3%). This inhibition occurred before the first action potential (AP) elicited by noise or tone bursts, was broadly tuned to tonal frequency and was shown to delay the first AP. Our data suggest it is a result of an intrinsic circuit activated by the octopus cell pathway originating in the contralateral cochlear nucleus; this pathway is known to convey exquisitely timed and broadly tuned onset information. This powerful inhibition within the VNLL appears to control the timing of this structure's inhibitory output to higher centers, which has important auditory processing outcomes. The circuit also provides a pathway for fast, broadly tuned, onset inhibition to the IC.
Internal Model of Gravity for Hand Interception: Parametric Adaptation to Zero-Gravity Visual Targets on Earth
Authors: Zago Myrka , Lacquaniti Francesco
Published: April 2005

Internal model is a neural mechanism that mimics the dynamics of an object for sensory motor or cognitive functions. Recent research focuses on the issue of whether multiple internal models are learned and switched to cope with a variety of conditions, or single general models are adapted by tuning the parameters. Here we addressed this issue by investigating how the manual interception of a moving target changes with changes of the visual environment. In our paradigm, a virtual target moves vertically downward on a screen with different laws of motion. Subjects are asked to punch a hidden ball that arrives in synchrony with the visual target. By using several different protocols, we systematically found that subjects do not develop a new internal model appropriate for constant speed targets, but they use the default gravity model and reduce the central processing time. The results imply that adaptation to zero-gravity targets involves a compression of temporal processing through the cortical and subcortical regions interconnected with the vestibular cortex, which has previously been shown to be the site of storage of the internal model of gravity.
Processing of Modulated Sounds in the Zebra Finch Auditory Midbrain: Responses to Noise, Frequency Sweeps, and Sinusoidal Amplitude Modulations
Authors: Woolley Sarah M. N. , Casseday John H.
Published: April 2005

The avian auditory midbrain nucleus, the mesencephalicus lateralis, dorsalis (MLd), is the first auditory processing stage in which multiple parallel inputs converge, and it provides the input to the auditory thalamus. We studied the responses of single MLd neurons to four types of modulated sounds: 1) white noise; 2) band-limited noise; 3) frequency modulated (FM) sweeps, and 4) sinusoidally amplitude-modulated tones (SAM) in adult male zebra finches. Responses were compared with the responses of the same neurons to pure tones in terms of temporal response patterns, thresholds, characteristic frequencies, frequency tuning bandwidths, tuning sharpness, and spike rate/intensity relationships. Most neurons responded well to noise. More than one-half of the neurons responded selectively to particular portions of the noise, suggesting that, unlike forebrain neurons, many MLd neurons can encode specific acoustic components of highly modulated sounds such as noise. Selectivity for FM sweep direction was found in only 13% of cells that responded to sweeps. Those cells also showed asymmetric tuning curves, suggesting that asymmetric inhibition plays a role in FM directional selectivity. Responses to SAM showed that MLd neurons code temporal modulation rates using both spike rate and synchronization. Nearly all cells showed low-pass or band-pass filtering properties for SAM. Best modulation frequencies matched the temporal modulations in zebra finch song. Results suggest that auditory midbrain neurons are well suited for encoding a wide range of complex sounds with a high degree of temporal accuracy rather than selectively responding to only some sounds.