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At least 1,747 records · Page 97Linked to original sources
PubMed1994

Modulation of adrenal cell functions by cadmium salts: 2. Sites affected by CdCl2 during unstimulated steroid synthesis.

In previous studies cadmium chloride (CdCl2) nonlethally inhibited Y-1 adrenal mouse adrenal tumour cell 20-dihydroxyprogesterone (20DHP) secretion, affecting unstimulated and stimulated steroidogenic pathway sites differently. We studied CdCl2 effects on unstimulated steroidogenesis using Y-1 cells incubated 0.5 h in medium with or without cadmium (using the concentration that inhibited ACTH-stimulated steroid secretion by 50%). Exogenously added 20-hydroxycholesterol (20OHC), 22(R)-hydroxycholesterol (22OHC), 25-hydroxycholesterol (25OHC), pregnenolone (PREG), or progesterone (PROG) were used to bypass any rate-limited steroidogenic pathway sites that CdCl2 might inhibit. 25OHC is a biologically active nonpathway steroid, while 20OHC, 22OHC, PREG, and PROG are pathway steroids; each increased unstimulated 20DHP secretion nearly 10-fold. Although CdCl2 could not reduce dibutyryl cyclic AMP- (dbcAMP)-stimulated 20DHP secretion significantly, it did significantly reduce basal and 25OHC-induced 20DHP secretion 25% below untreated levels. When 20OHC, 22OHC, PREG, or PROG were incubated with unstimulated Y-1 cells, their synthesis into 20DHP was unaffected by cadmium. dbcAMP bypasses the plasma membrane enzyme complex that synthesizes intracellular cAMP during exogenous ACTH stimulation; dbcAMP was not inhibited by CdCl2. The rate-limited step accelerated by cAMP involves plasma membrane and/or cytoplasmic cholesterol transport to and through outer and inner mitochondrial membranes before the cholesterol is synthesized into pregnenolone by side-chain cleavage enzymes on the inner membrane matrix face. Little is known regarding the mechanisms controlling unstimulated steroidogenesis. Under unstimulated conditions the 25-, 20- and 22(R)-monohydroxyls of cholesterol facilitate plasma membrane, cytoplasm and inner and outer mitochondrial solubility, diffusion and/or transport to bypass rate-limited steps and augment unstimulated steroid synthesis. Since conversion of endogenous mitochondrial cholesterol and 25OHC, but not dbcAMP-mobilized cytoplasmic cholesterol, 20OHC or 22OHC conversion, to 20DHP is inhibited by CdCl2, this suggests that (a) control of mitochondrial cholesterol supplies is independent of the cAMP-regulated mitochondrial steps in the 20DHP steroid synthetic pathway, (b) CdCl2 specifically inhibited endogenous mitochondrial cholesterol and 25OHC utilization, (c) CdCl2 toxicity may affect adrenal, testicular, ovarian, and placental basal steroidogenic functions, and (d) 25OHC may be a useful compound to examine unstimulated steroid synthesis.

Adrenal Glands↗
PubMed1994

Release of the nitric oxide precursor, arginine, from the thalamus upon sensory afferent stimulation, and its effect on thalamic neurons in vivo.

The neurophysiology and neuroanatomy of the thalamus have been extensively studied in a variety of species and sensory systems. The identity of the neurotransmitter(s) which mediate the excitation from ascending sensory afferents on to thalamic relay neurons is, however, still unclear, although it appears to be a substance which is a ligand for excitatory amino acid receptors, as the responses of ventrobasal thalamus neurons to natural stimulation of somatosensory afferents arising from the mustachial vibrissae of the rat are mediated by ionotropic excitatory amino acid receptors, when stimulation is performed using an air-jet directed at the vibrissa receptor field. In an effort to determine the transmitter of these sensory afferents, we have attempted to detect the release of amino acids in the ventrobasal thalamus in vivo upon such stimuli. We have thus used a similar natural stimulation protocol, together with push-pull perfusion and recording in the ventrobasal thalamus, and we describe the release of the amino acid, arginine, in this brain area following physiological stimulation of afferents. Furthermore, we show that application of L-arginine on to thalamic relay neurons can facilitate sensory synaptic transmission, possibly via the synthesis of the diffusable messenger, free radical gas, nitric oxide. This may represent a novel, local positive-feedback, modulatory system which could enhance the responsiveness of thalamic neurons to sensory input.

Afferent Pathways↗
PubMed2003

A comparative study of rotational atherectomy in acute and stable coronary syndromes in the modern era.

Percutaneous rotational coronary atherectomy (PRCA) is commonly used in the percutaneous treatment of diffuse, calcified coronary lesions in stable coronary syndromes (SCSs) and facilitates successful delivery and deployment of balloons and stents. Early experience with PRCA cautioned its use in acute coronary syndromes (ACSs). However, the evolution of the PRCA technique and improved antiplatelet pharmacotherapy has broadened its use in ACSs also. A total of 1,112 consecutive patients with an ACS (n=269) or SCS (n=843) who underwent PRCA of 1,483 lesions were examined retrospectively to evaluate the angiographic and short-term clinical outcomes. Troponin-I was elevated in 33.3% of the ACS group and in 0.6% of the SCS group at baseline (p<0.001). Angiographic complications occurred more frequently in the ACS group (18.6% vs 13.1%, p=0.02). There was no difference in major complications between the groups (ACS 1.1% vs SCS 0.8%; p=0.44). The incidence of any periprocedural creatinine kinase-MB elevation was 17.1% versus 18.9% (p=NS) and 30-day major adverse cardiac events (death, disabling stroke, creatine kinase-MB >3 times the upper limit of normal, urgent revascularization) was 5.9% versus 4.6% (p=NS) when comparing the ACS and SCS groups, respectively. With current techniques and antiplatelet therapy, PRCA can be safely performed in ACSs when lesion morphology dictates, with outcomes comparable to that achieved in SCSs. Although angiographic complications occurred more frequently in the ACS group, this did not result in a significantly higher incidence of postprocedural myonecrosis or 30-day major adverse cardiac events.

Acute Disease↗
PubMed2005

Armillaria luteobubalina mycelium develops air pores that conduct oxygen to rhizomorph clusters.

Armillaria luteobubalina produces air pores in culture. They consist of two parts: a basal region of tissue elevated to form a mound covered with a rind continuous with that of the colony, but perforated; and an apical region of long parallel hyphae, cemented together by scattered patches of extracellular material. This forms a hydrophobic structure that is elevated above the general level of the mycelial crust and does not easily become waterlogged. Air pores develop near the inoculum plug shortly after inoculation, arising directly from the mycelium, and rhizomorphs are initiated from them. The air pore contains a complex system of gas space connecting the atmosphere with the central canal of each rhizomorph. The tissue beneath the melanised colony crust also contains gas space, especially near air pores. This is also connected with the gas space of each rhizomorph and of each air pore. Measurements with oxygen electrodes show that air pores and their associated rhizomorphs conduct oxygen. The average oxygen conductance of a group of air pores with associated rhizomorphs, within agar blocks, but with rhizomorph apices cut off, was about 700 x 10(-12) m3s(-1), equivalent to about 200 x 10(-12) m3s(-1) for each air-pore. We conclude that the air pores conduct oxygen into the gas space below the pigmented mycelium of the colony, where the rhizomorphs - which also conduct oxygen - originate. A. luteobubalina thus has a complex aerating system which allows efficient diffusion of oxygen into rhizomorphs, and this is likely to facilitate extension of inoculum into low-oxygen environments.

Basidiomycota↗
PubMed1998

The influence of neuropeptides on Malpighian tubule writhing and its significance for excretion.

Diuretic peptides (locustakinin and Locusta-DH) increase the spontaneous contractile activity of visceral muscle fibers associated with Malpighian tubules from the migratory locust (Locusta migratoria) at concentrations that increase urine production. Muscle activity is shown to assist the flow of material in the tubule lumen, but is not essential for diuresis. Tubule writhing also serves to reduce unstirred layers (USLs) at the basolateral surface of the epithelium and thereby facilitates the excretion of solutes entering the lumen by passive diffusion.

Animals↗
PubMed2000

Gas-phase H/D exchange reactions of polyamine complexes: (M + H)+, (M + alkali metal+), and (M + 2H)2+

Gas-phase hydrogen/deuterium exchange reactions between noncovalent polyamine complexes and D2O, CH3OD, or ND3 are undertaken in a quadrupole ion trap mass spectrometer. Structural features of the protonated polyamines can be differentiated by the rates and overall extent of exchange, specifically the presence of propylene units and/or a cyclic structure noticeably decreases exchange compared to the exchange observed for acyclic polyamines with only ethylene bridges between amino groups. Significant differences are observed for singly protonated vs. doubly protonated complexes, where the doubly protonated complexes undergo more efficient exchange at a higher rate than the analogous singly protonated complexes. Molecular modeling calculations suggest that more diffuse conformations may exist for the higher charge states, thus facilitating H/D exchange. In addition, H/D exchange reactions between the alkali metal cationized complexes and ND3 are nearly quenched, compared to the significant exchange seen for singly protonated complexes. A conformational change or the loss of a low energy reaction pathway may explain the limited exchange reactions seen when a bulky cation replaces a proton in the complex.

Journal Article↗
PubMed2006

Supercritical CO2 extraction and purification of compounds with antioxidant activity.

Supercritical fluid extraction (SCFE), based on the utilization of a fluid under supercritical conditions, is a technology suitable for extraction and purification of a variety of compounds, particularly those that have low volatility and/or are susceptible to thermal degradation. The interest in SCFE is promoted by legal limitations of conventional solvents for food and pharmaceutical uses. The physicochemical properties of supercritical CO2 (higher diffusivity, lower viscosity, and lower surface tension than conventional solvents) facilitate mass transfer and allow an environmentally friendly operation. This article presents a comprehensive compilation of data on the supercritical CO2 extraction of antioxidant compounds from vegetal materials, with particular attention to those of a phenolic nature. Aspects concerning the supercritical operation for extraction and fractionation of antioxidants compounds are considered, including equilibrium solubility of pure compounds and effects of the operational conditions on the antioxidant activity of isolated fractions. The data are compared to those reported for synthetic antioxidants and natural extracts obtained by conventional solvent extraction from vegetal matrices.

Antioxidants↗
PubMed2000

Sintering dense nanocrystalline ceramics without final-stage grain growth

Sintering is the process whereby interparticle pores in a granular material are eliminated by atomic diffusion driven by capillary forces. It is the preferred manufacturing method for industrial ceramics. The observation of Burke and Coble that certain crystalline granular solids could gain full density and translucency by solid-state sintering was an important milestone for modern technical ceramics. But these final-stage sintering processes are always accompanied by rapid grain growth, because the capillary driving forces for sintering (involving surfaces) and grain growth (involving grain boundaries) are comparable in magnitude, both being proportional to the reciprocal grain size. This has greatly hampered efforts to produce dense materials with nanometre-scale structure (grain size less than 100 nm), leading many researchers to resort to the 'brute force' approach of high-pressure consolidation at elevated temperatures. Here we show that fully dense cubic Y2O3 (melting point, 2,439 degrees C) with a grain size of 60 nm can be prepared by a simple two-step sintering method, at temperatures of about 1,000 degrees C without applied pressure. The suppression of the final-stage grain growth is achieved by exploiting the difference in kinetics between grain-boundary diffusion and grain-boundary migration. Such a process should facilitate the cost-effective preparation of other nanocrystalline materials for practical applications.

Journal Article↗
PubMed2004

Spontaneous and controllable activation of suicide gene expression driven by the stress-inducible grp78 promoter resulting in eradication of sizable human tumors.

GRP78 is a stress-inducible chaperone protein with antiapoptotic properties that is overexpressed in transformed cells and cells under glucose starvation, acidosis, and hypoxic conditions that persist in poorly vascularized tumors. Previously we demonstrated that the Grp78 promoter is able to eradicate tumors using murine cells in immunocompetent models by driving expression of the HSV-tk suicide gene. Here, through the use of positron emission tomography (PET) imaging, we provide direct evidence of spontaneous in vivo activation of the HSV-tk suicide gene driven by the Grp78 promoter in growing tumors and its activation by photodynamic therapy (PDT) in a controlled manner. In this report, we evaluated whether this promoter can be applied to human cancer therapy. We observed that the Grp78 promoter, in the context of a retroviral vector, was highly activated by stress and PDT in three different types of human breast carcinomas independent of estrogen receptor and p53. Complete regression of sizable human tumors was observed after prodrug ganciclovir treatment of the xenografts in immunodeficient mice. In addition, the Grp78 promoter-driven suicide gene is strongly expressed in a variety of human tumors, including human osteosarcoma. In contrast, the activity of the murine leukemia virus (MuLV) long-terminal repeat (LTR) promoter varied greatly in different human breast carcinoma cell lines, and in some cases, stress resulted in partial suppression of the LTR promoter activity. In transgenic mouse models, the Grp78 promoter-driven transgene is largely quiescent in major adult organs but highly active in cancer cells and cancer-associated macrophages, which can diffuse to tumor necrotic sites devoid of vascular supply and facilitate cell-based therapy. Thus, transcriptional control through the use of the Grp78 promoter offers multiple novel approaches for human cancer gene therapy.

Animals↗
PubMed2005

Chronic cholinergic imbalances promote brain diffusion and transport abnormalities.

Cholinergic imbalances occur after traumatic effects and in the initial stages of neurodegenerative diseases, but their long-lasting effects remained largely unexplained. To address this, we used TgS transgenic mice constitutively overexpressing synaptic acetylcholinesterase (AChE-S) and presenting a complex phenotype of progressive neurodeterioration. T1- and T2-weighted magnetic resonance (MR) brain images appeared similar. However, diffusion-weighted MRI showed decreased baseline water apparent diffusion coefficient in the brains of TgS animals. Furthermore, contrast-enhanced MRI after gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) injection demonstrated slower recovery of normal signals in the TgS brains than with controls. Perfusion MR imaging and difference T1 maps calculated from pre- postcontrast T1-weighted MR images indicated accumulation of more Gd-DTPA molecules in the TgS brains than in the parent strain, reflecting impaired blood-brain barrier (BBB) functioning in these transgenic mice. To explore the molecular mechanism(s) underlying these global phenotypes, we performed microarray analysis in the stress-controlling prefrontal cortex of TgS vs. strain-matched wild-type animals. Profound overexpression of numerous ion channels, transporters, and adhesion genes was confirmed by real time RT-PCR tests. Immunohistochemical and immunoblot analyses revealed corresponding increases in the level and cellular distributions of the chloride channel CLCN3 and the water channel AQP4, both of which contribute to BBB maintenance. Our study attributes to balanced cholinergic neurotransmission, a central role in the brain's maintenance of water diffusion and ion transport, and indicates that chronic impairments in this maintenance facilitate neurodeterioration through interference with BBB function.

Acetylcholine↗
PubMed2002

Fast Kawasaki spin exchange limit of spin-facilitated kinetic Ising models.

We study a Fock-space operator technique for describing the stochastic kinetics of a spin-facilitated kinetic Ising model. We focus in particular on the diffusion (fast Kawasaki exchange) limit in which the kinetics can be described by a single mean field evolution equation. We derive some general criteria for the approximative validity of mean field theory for the case of a nondiverging diffusion coefficient of the local spin states.

Journal Article↗
PubMed2006

Critical roles for excretory-secretory cysteine proteases during tissue invasion of Paragonimus westermani newly excysted metacercariae.

Paragonimus westermani is a trematode parasite, which causes pulmonary and/or extrapulmonary granulomatous disease in humans. Successful invasion of the host tissue is critical for the survival of this tissue-invasive parasite. The enzymatic hydrolysis of host proteins is clearly a prerequisite of this process. In this study, we have investigated the functional roles of the excretory-secretory cysteine proteases of P. westermani newly excysted metacercariae (PwNEM) in tissue invasion. The 27 and 28 kDa enzymes (PwMc27 and PwMc28) purified from PwNEM excretory-secretory products (ESP), preferentially degraded fibrillar proteins, but not globular proteins. PwMc28 significantly facilitated the invasion of PwNEM into mouse peritoneum, whereas a diffusible cysteine protease inhibitor, trans-epoxysuccinyl-L-leuciloamido-(4-guanidino) butane (E-64) inhibited this process dose-dependently. Two distinct isoforms of PwMc28 (PwMc28a and PwMc28b), which exhibited two amino acid differences in their mature domains, were identified by tandem mass spectrometry and sequence analysis. Both enzymes were localized at the tegument on the anterior border and on the oral sucker, which suggests excretion-secretion via exocytosis or via the excretory canal network. The mRNA transcripts of PwMc28a and b were expressed abundantly during the active invasion/migration through the host's tissues, suggesting their relevant function to tissue invasion/migration in the definitive host.

Amino Acid Sequence↗
PubMed1981

The tsx protein of Escherichia coli can act as a pore for amino acids.

The tsx protein is known to be a specific diffusion pathway for nucleosides. The ability of this protein to facilitate the transport of molecules other than nucleosides was examined in strains lacking detectable amounts of porin (ompB mutants). The tsx protein was shown to promote serine, glycine, and phenylalanine transport and to have no effect on either glucose or arginine transport.

Amino Acids↗
PubMed1997

PHLOEM UNLOADING: Sieve Element Unloading and Post-Sieve Element Transport.

The transport events from the sieve elements to the sites of utilization within the recipient sink cells contribute to phloem unloading. The phenomenon links sink metabolism and/or compartmentation with phloem transport to, and partitioning between, sinks. The nature of the linkage depends upon the cellular pathway and mechanism of unloading. The common unloading pathway is symplasmic, with an apoplasmic step at or beyond the sieve element boundary reserved for specialized situations. Plasmodesmal conductivity exerts the primary control over symplasmic transport that occurs by diffusion with bulk flow anticipated to be of increasing significance as import rate rises. In the case of an apoplasmic step, efflux across the plasma membranes of the vascular cells occurs by simple diffusion, whereas efflux from nonvascular cells of developing seeds is facilitated and, in some cases, energy coupled. Accumulation of sugars from the sink apoplasm universally occurs by a plasma membrane-bound sugar/proton symport mechanism.

Journal Article↗
PubMed2000

[Mechanisms for tissue transport of fatty acids].

Fatty acids (FA) play an important role in energy metabolism. They are not only used as substrates for energy production but are also involved in many other metabolic pathways. However, the exact mechanisms by which FA are taken up by the cells are not yet fully understood. Fatty acids circulating in blood cross the cell membranes partly via a mechanism facilitated by plasma membrane proteins and partly via a passive diffusion mechanism, the former mechanism being of major importance.

Animals↗
PubMed2001

[The second tissue harmonic signal: from physics principles to clinical application].

The second harmonic signals received from organs are due to the non linear properties of tissue which cause distortion of the transmitted signal and are not primarily caused by the transmission of a harmonic frequency. The velocity of ultrasound propagation depends on the density of the insonified material. During the compression phase, the tissue becomes denser, and the ultrasound waves travel faster through the tissue than during the rarefaction phase; the compression phase tends to overtake the rarefaction phase. The ultrasound waveform thus, undergoes a distortion that becomes greater as the distance from the transducer increases. Due to these effects, the tissue tends to generate harmonics and hence shifts energy from the fundamental to the harmonic bands. There are several reasons why harmonic tissue imaging increases the signal-to-noise ratio and facilitates interpretation. In technically difficult patients, there is often a diffuse haze due to distortion of the transmitted beam by shallow surface layers or to reverberations between the skin and ribs. These distortions and reverberations consist almost entirely of ultrasound energy at the fundamental frequency. When the returned signal is filtered at the harmonic so as to reject the fundamental frequency, the clutter and haze are removed and the image becomes more clear and defined. A further reason for the decrease in artifacts and clutter is the side-lobe level reduction in the second harmonic beam. Thus, harmonic beams are narrower and have lower side-lobe levels than fundamental ones. There are several clinical applications of harmonic tissue imaging. These include the correct definition of endocardial borders resulting in an improved assessment of left ventricular function at rest as well as during stress testing, the delineation of the left atrial appendage, the detection of atrial right to left shunting, and left atrial spontaneous echo contrast. Moreover, improved endocardial visualization leads to better endocardial tracking with acoustic quantification and to more segments being interpretable with the anatomic M-mode.

Acoustics↗
PubMed2002

The structure of GlpF, a glycerol conducting channel.

The passage of water or small neutral solutes across the cell membrane in animals, plants and bacteria is facilitated by a family of homologous membrane channels, variously known as aquaporins though perhaps more correctly as aquaglyceroporins. The glycerol facilitator (GlpF) is a 28 kDa aquaglyceroporin that catalyses transmembrane diffusion of glycerol and certain linear polyhydric alcohols in Escherichia coli. X-ray crystallographic analysis of GlpF to 2.2 A resolution revealed an alpha-barrel structure, surrounded by six full-length transmembrane helices and two half-spanning helices that are joined head-to-head in the middle of the membrane. These helices are arranged to a quasi twofold manner relative to the central membrane plane, where highly conserved residues make helix-to-helix contacts that stabilize the relative position and orientation of the helices in the structure. This sequence-structure correlation suggests that the evolutionary divergence of aquaporins and aquaglyceroporins is constrained by a conserved structural framework within which specialized function may be developed. Three glycerol molecules were resolved in the central channel through the GlpF monomer, thereby defining a transmembrane channel for glycerol permeation. The structure of glycerol GlpF complex provides insight into the chemical basis for transmembrane selective permeability.

Amino Acid Sequence↗
PubMed2003

[Susac syndrome: a report of two cases].

OBJECTIVE: To investigate the clinic characters and diagnosis of Susac syndrome. METHODS: Two cases were systematically studied by the authors. RESULTS: All the two cases were young women. The clinical manifestations include acute and subacute multifocal and diffuse encephalopathic symptoms, hearing loss, and visual loss. Diagnosis is facilitated by demonstration of retinal arteriolar occlusions without uveitis or keratoconjunctivitis, mid-to-low frequency unilateral or bilateral sensorineural hearing loss, and numerous small foci of increased signal in the white and gray matter on T2-weighted brain magnetic resonance imaging. CONCLUSIONS: This rare syndrome often can be identified at an early stage with a careful history and physical examination. MRI, SPECT, retinal fluorescein angiography and audiometry will contribute to diagnosis.

Adult↗