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PubMed2000

Synthesis and characterization of a fluorescent substrate for the N-arachidonoylethanolamine (anandamide) transmembrane carrier.

N-Arachidonoylethanolamine (AEA) is a proposed endogenous ligand of the central cannabinoid receptor (CB1). Previous studies indicate that AEA is translocated across membranes via a process that has the characteristics of carrier-mediated facilitated diffusion. To date, studies of this mechanism have relied on [(3)H]AEA as a substrate for the carrier. We have synthesized an analog of AEA, SKM 4-45-1, that is nonfluorescent in the extracellular environment. When SKM 4-45-1 is exposed to intracellular esterases, it is de-esterified and becomes fluorescent. We have carried out studies to demonstrate that SKM 4-45-1 accumulation in cells occurs via the AEA carrier. SKM 4-45-1 is accumulated by both cerebellar granule cells and C6 glioma cells. Uptake of SKM 4-45-1 into C6 glioma is inhibited by AEA (IC(50)=53.8 +/- 1.8 microM), arachidonoyl-3-aminopyridine amide (IC(50)=10.1 +/- 1.4 microM), and arachidonoyl-4-hydroxyanilineamide (IC(50)=6.1 +/- 1.3 microM), all of which also inhibit [(3)H]AEA accumulation. Conversely, [(3)H]AEA accumulation by cerebellar granule cells is inhibited by SKM 4-45-1 with an IC(50) of 7.8 +/- 1. 3 microM. SKM 4-45-1 is neither a substrate nor inhibitor of fatty acid amide hydrolase, an enzyme that catabolizes AEA. SKM 4-45-1 does not bind the CB1 cannabinoid receptor at concentrations <10 microM. In summary, the cellular accumulation of SKM 4-45-1 occurs via the same pathway as AEA uptake and provides an alternative substrate for the study of this important cellular process.

Amidohydrolases↗
PubMed2000

Pharmacological properties of Y-27632, a specific inhibitor of rho-associated kinases.

Y-27632 [(+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide++ + dihydrochloride] is widely used as a specific inhibitor of the Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK) family of protein kinases. This study examined the inhibition mechanism and profile of actions of Y-27632 and a related compound, Y-30141 [(+)-(R)-trans- 4-(1-aminoethyl)-N-(1H-pyrrolo[2, 3-b]pyridin-4-yl)cyclohexan-ecarboxamide dihydrochloride]. Y-27632 and Y-30141 inhibited the kinase activity of both ROCK-I and ROCK-II in vitro, and this inhibition was reversed by ATP in a competitive manner. This suggests that these compounds inhibit the kinases by binding to the catalytic site. Their affinities for ROCK kinases as determined by K(i) values were at least 20 to 30 times higher than those for two other Rho effector kinases, citron kinase and protein kinase PKN. [(3)H]Y-30141 was taken up by cells in a temperature- and time-dependent and saturable manner, and this uptake was competed with unlabeled Y-27632. No concentrated accumulation was found, suggesting that the uptake is a carrier-mediated facilitated diffusion. Y-27632 abolished stress fibers in Swiss 3T3 cells at 10 microM, but the G(1)-S phase transition of the cell cycle and cytokinesis were little affected at this concentration. Y-30141 was 10 times more potent than Y-27632 in inhibiting the kinase activity and stress fiber formation, and it caused significant delay in the G(1)-S transition and inhibition of cytokinesis at 10 microM.

3T3 Cells↗
PubMed1975

Carbohydrate absorption. Studies on the glucose transport by isolated brush border membranes. A contribution towards an understanding of the molecular mechanism of sugar absorption.

From investigations, mainly on intact in vitro preparations of small intestine, it has been established that the epithelial cell carries out digestion as well as absorption of carbohydrates, i.e. the luminal (brush border) plasma membrane contains di- and poly-saccharidases for the degradation of carbohydrates to monosaccharides as well as transport systems for monosaccharides. Recently, an intact glucose transport system has been demonstrated in isolated membranes from rat intestinal brush borders. In the isolated membranes, glucose transport has the characteristics expected for 'facilitated diffusion' of glucose coupled to Na+ translocation. The Na+-dependent uptake of glucose can be influenced by electrical potentials across the brush border membrane, which indicates that the positive charge of Na+, associated with sugar uptake, is not compensated by the counter-movement of another cation, e.g. K+, or by the co-movement of an anion via the same glucose 'carrier'. In other words, the Na+-coupled D-glucose transport is linked to a charge translocation - it is electrogenic. The apparent Na+ independence of glucose transport in vivo and the accumulation of glucose against a glucose as well as a Na+ concentration gradient by isolated epithelial cells may be explained by the 'ion gradient' model of Crane and Schultz and Zalusky provided the electrical membrane potential is high under these conditions and the electrochemical potential of Na+ serves as driving force for 'active' glucose transport.

Animals↗
PubMed1975

Vitamin passage across the placenta.

A pregnant woman who has adequate nutrition available in the form of a standard diet will provide the vitamins required by the fetus for normal development. Active transport of the water-soluble vitamins plus easy oral absorption after birth insure nutritional sufficiency at any gestational age. The fat-soluble vitamins which have a much slower transfer rate as the result of facilitated diffusion do not achieve the same degree of storage in the developing fetus. Thus, the premature infant who has decreased stores and who may have impaired oral absorption initially may become deficient in a fat-soluble vitamin (A, D, E, K) during the first 4 to 6 weeks of life. Oral or possibly parenteral supplementation following birth, however, would seem more appropriate than subtoxic doses administered to the mother prenatally.

Ascorbic Acid↗
PubMed2000

Dialysate flow distribution in hollow fiber hemodialyzers with different dialysate pathway configurations.

UNLABELLED: The efficiency of a hemodialyzer is largely dependent on its ability to facilitate diffusion, since this is the main mechanism by which small solutes are removed. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. The objective of the paper was to study the impact of different dialysate compartment designs on dialysate flow distribution and urea clearances. Eighteen hollow fiber 1.3 m2 hemodialyzers were studied, 6 each of 3 designs: Type A--standard fiber bundle (PAN 65DX Asahi Medical, Tokyo, Japan); Type B--spacing filaments external to the fibers (PAN 65SF Asahi Medical, Tokyo, Japan); Type C--fibers waved to give Moiré structure (FB130 Nissho-Nipro, Osaka, Japan). IN VITRO STUDIES: 3 dialyzers of each type were studied following dye injection into the dialysate compartment. Dynamic sequential imaging of longitudinal sections of the dialyzer were undertaken, using a new generation helical CT scanner (X-Press/HS1 Toshiba Corporation, Tokyo, Japan). In vivo studies: 3 dialyzers of each type were studied, in randomized sequence, in 3 different patients under standardized dialysis conditions. Blood- and dialysate-side urea clearances were measured at 30 and 150 minutes of treatment. Macroscopic and densitometrical analysis revealed that flow distribution was most homogeneous in the dialyzer with Moiré structure (Type C) and least homogeneous in the standard dialyzer (Type A). Space yarns (Type B) gave an intermediate dialysate flow distribution. Significantly increased urea clearances (p<0.001) were seen with Types B and C, compared to the standard dialyzer. Type C (Moiré) had the highest clearances although these were not significantly greater than Type B (space yarns). In conclusion, more homogeneous dialysate flow distribution and improved small solute clearances can be achieved by use of spacing yarns or waved (Moiré structure) patterns of fiber packing in the dialyzer. These effects are achieved probably as a result of reduced dialysate channeling resulting in a lower degree of mismatch between blood and dialysate flows. The new radiological technique using the helical CT scanner allows detailed flow distribution analysis and has the potential for testing future modifications to dialyzer design.

Equipment Design↗
PubMedDate not supplied

Fluoride content of infant formulas prepared with deionized, bottled mineral and fluoridated drinking water.

Usually infant milk formula is the major source of fluoride in infancy. Fluoride concentrations in ten samples of powdered milk formulas, prepared with deionized, bottled mineral, and fluoridated drinking water were determined after HMDS-facilitated diffusion, using a fluoride ion specific electrode(Orion 9609). Fluoride concentrations ranged from 0.01 to 0.75 ppm; from 0.02 to 1.37 ppm and from 0.91 to 1.65 ppm for formulas prepared with deionized, bottled mineral (0.02 to 0.69 ppm F) and fluorinated drinking water (0.9 ppm F), respectively. Possible fluoride ingestion per Kg body mass ws estimated. With deionized water, only the soy-based- formulas should provide a daily fluoride intake of above the suggested threshold for fluorosis. With water containing 0.9 ppm F, however, all of them would provide it. Hence, to limit fluoride intakes to amounts <0.1 mg/kg/day, it is necessary to avoid use fo fluoridated water (around 1 ppm) to dilute powdered infant formulas.

Animals↗
PubMedDate not supplied

Amifostine (Ethyol) as modulator of hepatic and biliary toxicity from intraarterial hepatic chemoembolization: results of a phase I study.

BACKGROUND/AIMS: Hepatic and biliary toxicity are still significant problems after intraarterial hepatic chemoembolization for liver metastases from large bowel cancers. In about 30-60% of the patients hepatic and biliary toxicity are the limiting aspects of intraarterial hepatic chemoembolization and exclude a lot of patients from a repeated beneficial treatment. Amifostine (Ethyol) is a prodrug that must be dephosphorylated to the free thiol in which form it can detoxify free oxygen radicals generated by radiation, hypoxia and by drugs such anthracyclines, platinum analogues and alkylating agents. Amifostine as inactive prodrug is primarily metabolized at the tissue site by membrane alkaline phosphatase, which is highly active in the cell membranes of normal endothelial cells and biliary tree cells but not in the cell membranes and neovascular capillaries of tumor. When dephosphorylated to WR-1065, amifostine is rapidly taken up into normal liver cells by a carrier-mediated facilitated diffusion transport process. The resulting high thiol content in normal liver tissue (biliary cells and hepatocytes) compared with the negligible concentration in liver metastases from large bowel cancers probably provides for selective drug resistance to intraarterial hepatic chemoembolization protecting normal tissue and allowing full therapeutic effect on tumor. METHODOLOGY: From May 1997 we planned a phase I study in patients receiving intraarterial hepatic chemoembolization for liver metastases from large bowel cancers. We started at 200 mg/m2 dissolved in 250 cc of normal saline given in 15 min in the intrahepatic artery 20 min before an intraarterial hepatic chemoembolization consisting of mitomycin 10 mg/m2, epirubicin-50, cisplatin-60 diluted in 10 mL of contrast media, mixed in 15 mL of lipiodol UF followed by a gelfoam powder solution until stagnation of the flow. The escalating dose, every 3 patients, was: 200 mg/m2, 250 mg/m2, 300 mg/m2, 350 mg/m2. RESULTS: Toxicity has been observed at 350 mg/m2: 1 patient reported transient hypotension (Blood pressure 70/50 mm Hg), 1 patient had skin flushing and dyspnoea. 300 mg/m2 are well tolerated and seem to reduce the level of transaminases, lactic acid dehydrogenase, and gamma-glutamyl transferase. Also the duration of necrotic damage, always observed after intraarterial hepatic chemoembolization, seems shorter compared with historical controls. CONCLUSIONS: Amifostine can be certainly administered at 300 mg/m2 as intraarterial infusion and could be a significant step to ameliorate the therapeutic ratio of intraarterial hepatic chemoembolization.

Amifostine↗
PubMed2002

Blood and dialysate flow distributions in hollow-fiber hemodialyzers analyzed by computerized helical scanning technique.

The efficiency of a hemodialyzer is largely dependent on its ability to facilitate diffusion between blood and dialysis solution. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. This article describes the distribution of the blood and dialysate flows in hollow-fiber hemodialyzers analyzed with a computerized scanning technique. Blood flow distribution was studied in vitro by dye injection in the blood compartment during experimental extracorporeal circulation using human blood with hematocrit (Hct) adjusted at 25 and 40%. Sequential images were obtained with a helical scanner in a 1-cm-thick fixed longitudinal section of the dialyzer. Average and regional blood flow velocity and wall shear rates were measured by using the reconstructed imaging sequence. The method allowed the calculation of single-fiber blood flow and single-fiber wall shear rate (SF wSh) in different regions of the hemodialyzer. In 38 patients on chronic hemodialysis, creatinine and phosphate clearance displayed a significantly negative correlation with Hct (P < 0.05), but this correlation was not found for urea, although a trend toward reduction could be observed. The suggested explanation of this phenomenon is the significant reduction in effective plasma water flow across the hemodialyzer in presence of a progressive rise in Hct. The second explanation for this phenomenon may be found in the nonhomogeneous distribution of blood flow within the fibers observed at the sequential imaging. This, in fact, could also explain the negative trend observed for urea. At higher Hct levels, single-fiber blood flow velocity and SF wSh were significantly lower in the fibers situated at the periphery of the bundle. At the same time, SF wSh tended to decrease in peripheral fibers, showing a value near half of that observed in the central fibers of the bundle (165 versus 301 s(-1)). A similar technique was used to study the flow distribution in the dialysate compartment in three different types of hemodialyzers with characteristic dialysate compartment design: (A) standard configuration; (B) space yarns (spacing filaments preventing contact between fibers); and (C) Moiré structure (wave-shaped fibers to prevent contact between adjacent fibers). Clinical sessions of hemodialysis were also carried out to measure blood- and dialysate-side urea clearances in the different hemodialyzers. Macroscopic and densitometric analysis revealed that flow distribution was most homogeneous in the dialyzer with Moiré structure (type C) and least homogeneous in the standard dialyzer (type A). Space yarns (type B) gave an intermediate dialysate flow distribution. Urea clearance (P < 0.001) increased significantly with types B and C, compared with the standard dialyzer. Type C had the highest clearances, although they were not significantly greater than type B. In conclusion, a significant blood-to-dialysate flow mismatch may occur in hollow-fiber hemodialyzers due to either uneven blood flow distribution or a dialysate channeling phenomenon external to the fiber bundle. Improvement in dialyzer design may overcome these problems, at least in part.

Aged↗
PubMed1975

Stimulation of 3-O-methylglucose transport by anaerobiosis in rat thymocytes.

Transport of 3-O-methylglucose by rat thymocytes occurs by facilitated diffusion and follows a biphasic time course. The half-times of the two phases of uptake are 0.8 min and 20 to 30 min; the rapid phase contributes 10 to 20% of the total 3-O-methylglucose taken up at equilibrium. Cells incubated under anaerobic conditions for 1 hour undergo a 3- to 4-fold increase in the initial rate of 3-O-methylglucose uptake. The relative contribution of the rapid phase of uptake increases nearly 4-fold in anaerobically incubated cells, although the half-time of the rapid phase remains the same. Anaerobiosis also reduces the half-time of the slow phase of uptake by a factor of three. In the absence of exogenous glucose, anaerobiosis reduces cellular ATP by 97% after 1 hour at 37 degrees. However, full stimulation of transport activity does not occur in cells with such low levels of ATP. When anaerobically incubated cells are re-exposed to oxygen, ATP synthesis proceeds and transport activity increases by 100% within 5 to 10 min. Adding 1 mM 2,4-dinitrophenol at the time the anaerobic cells are reexposed to oxygen completely blocks the subsequent ATP synthesis and the associated increase in transport activity. Cells incubated aerobically in the presence of 1 mM 2,4-dinitrophenol show a 90% reduction in ATP levels and a 2-fold increase in the rate of 3-O-methylglucose uptake. An additional 70% increase in transport activity is observed when the cells are washed free of uncoupler and incubated an additional 10 min. The results suggest that transport activity is stimulated when cellular ATP levels decline but that the stimulation process requires some minimal level of ATP for full expression.

Aerobiosis↗
PubMedDate not supplied

[Detection of microorganisms in the environment and the preliminary appraisal of their physiological state by X-ray microanalysis].

The paper deals with the X-ray microanalysis of the elemental composition of bacteriomorphic particles in 170,000-year old Antarctic permafrost sediments and in indoor dust. A comparative analysis of the phosphorus, sulfur, calcium, and potassium contents and the Ca/K and P/S ratios in these particles and in reference microbial cells occurring in different physiological states showed that the absence of P and/or S peaks in the X-ray spectrum of an object may indicate that it is abiotic. Resting microbial forms can be revealed on the basis of the following characteristic features: an increased content of Ca, a high Ca/K ratio, and a low P/S ratio. Model experiments with nonviable bacterial and yeast micromummies with alterations in the structural and barrier functions of the cytoplasmic membrane showed that micromummies can be recognized by a super-high content of a marker element (e.g., P, K, or Si), accumulated due to facilitated diffusion along the deliberately created concentration gradient. Such an analysis of the permafrost sediment and dust made it possible to suggest the presence of mummified cells in these objects. The possibility of using X-ray microanalysis for the detection of microbial cells in natural habitats in order to enhance the efficiency of ecological monitoring of the environment is discussed.

Antarctic Regions↗
PubMed2004

Immunohistochemical detection of glucose transporters class I subfamily in the mouse, rat and human testis.

A family of glucose transporters (GLUT) mediates the cellular uptake of glucose at the plasma membrane by facilitated diffusion. We investigated the presence of isoforms GLUT1-4 of class I subfamilies in different types of cells in the mouse, rat and human testis by indirect immunofluorescence technique. Immunocytochemical analyses demonstrated that GLUT1 was expressed in the rat testis, GLUT2 in the mouse and rat testis, GLUT3 in the mouse, rat and human testis and GLUT4 was not presented in the testis at all. A very intensive positive immunoreaction for GLUT3 was found in Sertoli cells, peritubular myoid cells, macrophage-like interstitial cells, testicular endothelial cells and early spermatocytes. GLUT3 positive cells were not found in the luminal part of Sertoli cells, spermatids or Leydig cells. The present results suggest that glucose uptake in different testicular cells is mediated by GLUT1, GLUT2 and GLUT3 and the GLUT3 was the prominent glucose transporter type in the testicular cells.

Animals↗
PubMed2004

Transport proteins in rats' renal corpuscle and tubules.

UNLABELLED: The localization of transepithelial transport proteins for glucose and water reabsorption in renal corpuscle and tubules epithelium was observed. MATERIAL AND METHODS: Immunohistochemistry of normal male Wistar rats' kidney has been performed. Facilitated diffusion glucose transporter GLUT4, Na(+)-dependent glucose co-transporter SGLT1, a cargo transporter TGN38, and water transporter aquaporin-2 (AQP2) were used. RESULTS: An intensive GLUT4 expression in renal proximal tubules and in convoluted segment of distal tubules has been observed. The intensive SGLT1 expression was marked in all renal tubules, and also in the glomerulus of the renal corpuscle. TGN38 was expressed mainly in the S1 of proximal tubules and a bit weaker in the distal tubules. The most intensive AQP2 expression in the proximal tubules and in the thin part of Henle's loop has been detected. In some cases AQP2 expression in the collecting tubules has been observed. The same tubules nephroni are marked heterogeneously. The distribution of transepithelial transport proteins in different parts of nephroni is also greatly heterogeneous because of weak determination of urinary system. CONCLUSION: The comparable transport-proteins distribution with technique of fluorescence immunohistochemistry in rats' renal corpuscle and tubules was elucidated. Data suggest that expression of glucose and water transepithelial transporter proteins is heterogeneous in all parts of nephron, and, probably, is in accordance with recycling of transport proteins.

Animals↗
PubMedDate not supplied

Risk of fluorosis associated with infant formulas prepared with bottled water.

PURPOSE: The purpose of this study was to estimate fluoride (F) intake from infant formulas prepared with different brands of bottled water. METHODS: Fluoride concentrations in 4 samples of infant milk and soy-based formulas, commercially available in the United States, prepared with deionized water and 5 brands of bottled water, were determined after Hexamethyldisioxane (HMDS)-facilitated diffusion, in duplicate, using an F ion-specific electrode. Possible fluoride ingestion per killogram body mass was estimated, based on suggested volumes of formula consumption, for infants 1 and 12 months. RESULTS: Fluoride concentrations ranged from 0.076 to 0.214 ppm and 0.092 to 1.053 ppm for formulas prepared with deionized and bottled water, respectively. When prepared with deionized water, none of the formulas provided an F intake above the suggested threshold for fluorosis (0.07 mg F/kg/day). However, when prepared with some brands of bottled water containing 0.623 and 0.839 ppm, all of them did provide it. CONCLUSIONS: Some brands of bottled water usually marketed for infants and used to dilute infant formulas may increase fluoride concentrations beyond reccommended levels believed to lead to fluorosis.

Fluorides↗
PubMedDate not supplied

Nails as biomarkers of fluoride in children of fluoridated communities.

PURPOSE: The objective of this study was to verify the use of nails as biomarkers of chronic fluoride (F) exposure from the diets of children living in communities with negligibly or optimally fluoridated water. METHODS: Fifteen 2- to 6-year-old children living in Bauru-São Paulo (fluoridated) and 15 lifelong residents of Itápolis-São Paulo (nonfluoridated) participated in the study. Fluoride concentrations in nails and duplicate diet were analyzed with the electrode, following hexamethyldisiloxane (HMDS)-facilitated diffusion. Data were analyzed by student's t-test and linear regression (P < .05). RESULTS: Mean fluoride concentrations ([microg/g) in fingernails and toenails of Bauru children were 3.56 +/- 1.3 and 2.81 +/- 1.29, respectively, and for Itápolis children 2.29 +/- 1.25 and 1.58 +/- 0.59, respectively. The differences between Bauru and Itápolis children, as well as between fluoride concentrations in fingernails and toenails, were statistically significant. The estimated fluoride intake from the diet was significantly higher for Bauru children (0.55 +/- 0.61 mg) when compared to Itápolis children (0.09 +/- 0.06 mg). A significant positive correlation was found between the mean of fingernail and toenail fluoride concentrations and estimated fluoride intake from the diet (r = 0.57). CONCLUSIONS: This study's preliminary data suggests that fingernails and toenails may be used as biomarkers of chronic fluoride exposure from the diet. Additional studies are necessary to determine the predictive values, sensitivity, and specificity of this biomarker so that nails are used to differentiate children at the age of dental fluorosis risk and who live in communities with negligibly or optimally fluoridated water.

Biomarkers↗
PubMed2005

The mystery of phospholipid flip-flop in biogenic membranes.

Phospholipid flip-flop is required for bilayer assembly and the maintenance of biogenic (self-synthesizing) membranes such as the eukaryotic endoplasmic reticulum and the bacterial cytoplasmic membrane. Due to the membrane topology of phospholipid biosynthesis, newly synthesized phospholipids are initially located in the cytoplasmic leaflet of biogenic membranes and must be translocated to the exoplasmic leaflet to give uniform bilayer growth. It is clear from many studies that phospholipid flip-flop in biogenic membranes occurs very rapidly, within a period of a few minutes. These studies also reveal that phospholipid translocation in biogenic membranes occurs bi-directionally, independently of the phospholipid head group, via a facilitated diffusion process in the absence of metabolic energy input, and that this type of transport requires specific membrane proteins. These translocators have been termed biogenic membrane flippases, and they differ from metabolic energy-dependent transporters (ABC transporters and MDR proteins). No biogenic membrane flippases have been characterized. This review briefly discusses the importance of biogenic membrane flippases, the various assay methods used for measuring the rate of phospholipid flip-flop, and the progress that has been made towards identifying these proteins.

Animals↗
PubMed2005

Monitoring fluoride exposure with fingernail clippings.

The purpose of this review is to discuss new information regarding the relationship between the level of fluoride exposure and the corresponding fluoride concentrations in fingernail clippings. While there are several techniques available to extract fluoride from fingernails prior to analysis with the electrode, the HMDS-facilitated diffusion method is the most popular. Fluoride enters fingernails at the growth end and reaches the distal end approximately three months later. The fluoride concentration in the clipping reflects the average fluoride intake and plasma concentration during the period when the clipping was formed. Therefore, the concentration in the clipping is directly related to the average fluoride exposure that occurred during a 1-2 week period (depending on the length of the clipping) about three months ago and not to recent and possibly variable exposures that occur during the day. Published studies have demonstrated that fingernail fluoride concentrations reflect fluoride exposures from drinking water, toothpaste and the work environment and can be expected to do so for any source of intake including salt.

Cariostatic Agents↗
PubMed2005

The anti-thrombotic activity of surfactins.

Platelet aggregation was inhibited and the density of platelet-rich plasma (PRP) clots was decreased by the preincubation of PRP with surfactins, an acidic lipopeptide of Bacillus subtilis complex BC1212 isolated from soybean paste, in dose-dependent manner. Our findings suggest that surfactins are able to prevent a platelet aggregation leading to an inhibition of additional fibrin clot formation, and to enhance fibrinolysis with facilitated diffusion of fibrinolytic agents.

Bacillus subtilis↗
PubMedDate not supplied

Characteristics of glucose transport across the microvillous membranes of human term placenta.

Transport characteristics of D-glucose were studied in the microvillous vesicles isolated from the human term placenta. Transport occurred by selective and rapid facilitated diffusion system which was inhibitable by phloretin and HgCl2. The transport was dependent on a transmembrane. Na+-gradient indicating a "secondary active transport" system operating. The transport influx was saturable and the kinetic analysis based on Hanes-Woolf plot produced a kt and Jmax value of 1.2 mM and 34 nmoles.mgprotein(-1).min(-1), respectively. The efflux of D-glucose from the membrane vesicles in a pre-equilibrated assay conditions showed a distinct biphasic pattern differing significantly in the half time efflux. The t1/2 of the fast and slow components was found to be 15 sec and 660 sec, respectively. The transport showed distinct sensitivity to temperature and the Ea values both below and above the transition temperature of 37 degrees C, as calculated from the Arrhenius plot were found to be 7600 and 5472 kCal.mol(-1), respectively. Inhibition studies with a number of sugars for hexose transport pathway showed that the glucose epimers, phosphorylated sugars, and even the disaccharides and the pentose sugars competed effectively with D-glucose. The influx was also inhibited by a number of steroids such as progesterone, 17alpha-hydroxyprogesterone, testosterone and estrogen. Insulin was found to increase glucose transport in a dose- dependent fashion at a concentration of 0.2-1 unit.ml(-1). Ouabain, dinitrophenol and nicotine strongly inhibited D-glucose uptake in the membrane vesicles.

Biological Transport, Active↗