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At least 757 records · Page 42Linked to original sources
PubMed1991

Effect of transport time and FiO2 on SpO2 during transport from the OR to the PACU.

Early postoperative hypoxemia may be due to a reduced functional residual capacity, hypoventilation, and ventilation-perfusion mismatch. These factors reduce the partial pressure of the arterial oxygen which ultimately reduces the oxygen transported to the tissues by decreasing the hemoglobin saturation. This may lead to cellular ischemia and death. Oxygen saturation may decrease during transport from the operating room to the postanesthesia care unit. The length of transport time in large operating suites may exceed 5 minutes, which may lead to inadequate oxygenation. This research used a pretest-posttest control group design on a convenience sample. Subjects were randomized into either the treatment or control group. At emergence, the SpO2 measured and the stopwatch started. The treatment group received 40% oxygen via a venturi mask during transport while the control group breathed room air. After a routine transport to the postanesthesia care unit, the SpO2 was again measured and the transport time was recorded. Oxygen saturation was found to be significantly greater in the group breathing supplemental O2 during transport.

Adult↗
PubMed1985

Monoclonal antibodies to the glucose transporter from human erythrocytes. Identification of the transporter as a Mr = 55,000 protein.

Using the preparation of purified glucose transporter from human erythrocytes as antigen, we have prepared and characterized six monoclonal antibodies. Three of these antibodies have been shown to be to the glucose transporter by several criteria: they immunoprecipitate the transport activity, the cytochalasin B binding activity, and 75% of the protein from the solubilized purified preparation. The remaining three antibodies were shown to recognize the same polypeptide by a Western blot procedure. All of the antibodies reacted with the deglycosylated transporter and are thus against peptide determinants; most bound to the cytoplasmic domain of the transporter. The antibodies exhibited a range of effects on cytochalasin B binding, from slight enhancement to modest inhibition to strong inhibition; for this reason they must bind to at least three different epitopes. Western blot analysis of erythrocyte membranes prepared in the presence of protease inhibitors showed that all six antibodies bound to a polypeptide of average Mr = 55,000. Moreover, by immunological assay this polypeptide accounted for 5.3% of the membranes protein, a value similar to that given by cytochalasin B binding. Thus, the proposal that the native transporter is a Mr = 100,000 polypeptide is highly unlikely. The antibodies also react with the glucose transporter in other human cell types, but not with that in rodent or avian cells.

Animals↗
PubMed1989

Transportation of rats affects behaviour of non-transported rats in the absence of physical contact (preliminary communication).

We have studied the effect of transportation stress in one rat on the behaviour of another, non-transported rat in the absence of physical contact. For this purpose an open box consisting of two adjacent small fields was used. Rats were placed in these fields and their behaviour was assessed. The control measurement involved pairs of non-transported rats and the experimental pairs consisted of a transported and a non-transported rat. The non-transported rats of the experimental pairs displayed significantly increased activities of sniffing when compared with the non-transported rats of the control pairs. It is suggested that stressed animals can influence the behaviour of nearby animals.

Animals↗
PubMed1985

Rapid kinetics of the glucose transporter from human erythrocytes. Detection and measurement of a half-turnover of the purified transporter.

The stopped flow method combined with fluorescence detection has been employed to study the rapid kinetics of the glucose transporter from human erythrocytes. Upon mixing the purified transporter reconstituted into unsealed membranes of erythrocyte lipids with 4,6-ethylidene D-glucose, a derivative that binds preferentially to the substrate site on the outer domain of the transporter, there was a rapid, first-order decrease in the intrinsic fluorescence of the protein. Three properties of this transient indicate that it represents a half-turnover of the transporter from a conformation with the substrate site facing inward to one with this site facing outward. The first-order rate constant decreased as the concentration of ethylidene glucose was increased; the value of the rate constant for the process is similar to that expected from steady-state kinetic studies of transport in the erythrocyte; and D-glucose at low concentration increased the rate of reaction. This study is the first determination of the kinetics of a half-turnover for a transport system of the facilitated diffusion type. The identification of this step provides direct evidence for the alternating conformation mechanism of transport.

Carrier Proteins↗
PubMed1984

One transporter per vesicle: determination of the basis of the insulin effect on glucose transport.

The basis for insulin stimulation of glucose transport in rat adipocytes has been investigated by determining the relative number of functional glucose transporters in the plasma and microsomal membranes from basal and insulin-treated cells. Each fraction was solubilized with cholate and then reconstituted into vesicles of about 500 A in diameter through removal of the cholate by dialysis. This procedure distributed the glucose transporters into the vesicles at a density of either one or none per vesicle. Consequently the fraction of the intravesicular volume that rapidly equilibrated with D-glucose provided an estimate of the relative number of functional transporters. By means of this one-transporter-per-vesicle method, it was found that insulin increased the number of transporters in the plasma membrane by a factor of 2.4 and decreased the number in the microsomes to 68% of the original value. These results provide independent evidence for the hypothesis that insulin causes the translocation of functional transporters from an intracellular location to the plasma membrane.

Adipose Tissue↗
PubMed1994

Hepatic Na(+)-independent amino acid transport in endotoxemic rats: evidence for selective stimulation of arginine transport.

The effects of endotoxin on the activities of the major Na(+)-independent amino acid transporters in rat liver (Systems n, asc, L, bo,+, and y+) were studied using using hepatic plasma membrane vesicles (HPMVs). Rats were treated with a single dose of Escherichia coli endotoxin (E. coli lipopolysaccharide 0127:B8 (LPS), 7.5, 15, or 30 mg/kg BW) and HPMVs were prepared by Percoll density gradient centrifugation at various timepoints after LPS administration. Vesicle purity and integrity was established by assay of enzyme markers and identical equilibrium uptakes. The activities of the Na(+)-independent amino acid transport systems y+ and bo,+ (arginine), asc (alanine and cysteine), L (leucine), and n (glutamine) were evaluated by measuring the uptake of radiolabeled amino acids using a rapid mixing/filtration technique. Amino acid uptake by HPMVs consisted of saturable and nonsaturable components. Prior treatment with endotoxin did not alter the activities of Systems n, asc, or L but resulted in a time- and dose-dependent stimulation of saturable arginine transport. Arginine transport increased within 2 h of LPS administration and exhibited a return towards basal levels by 24 h. Nonsaturable uptake (diffusion) in HPMVs was unaltered by LPS treatment. Kinetic analysis of arginine transport demonstrated the presence of both a high affinity and a low affinity carrier. Treatment with LPS resulted in a 73% increase in the Vmax of the high affinity carrier (System y+) and a 25% increase in the Vmax of the low affinity transporter (System bo,+). The data indicate selective stimulation of Na(+)-independent arginine transport in the liver during endotoxemia which may serve to support important arginine-dependent pathways during sepsis.

Analysis of Variance↗
PubMed1994

Transcellular transport of oral cephalosporins in human intestinal epithelial cells, Caco-2: interaction with dipeptide transport systems in apical and basolateral membranes.

The transport characteristics of p.o. cephalosporin antibiotics by monolayers of the human intestinal epithelial cell line Caco-2 were examined by measuring intracellular accumulation and transcellular transport. In the presence of an inward H+ gradient (at pH 6.0 of the apical medium), cephalosporins were accumulated by the monolayers in the following order: ceftibuten (anion) > cephradine (zwitterion) > cephalexin (zwitterion) > cefixime (anion). The accumulation rate of ceftibuten was more rapid than that of cephradine, whereas both appeared at the same rate in the basolateral compartment. The efflux of ceftibuten from the monolayers to the basolateral compartment was lower than the efflux of cephradine. The accumulation rate of ceftibuten from the basolateral side was markedly lower than that of cephradine. The accumulation of ceftibuten from both the apical and basolateral compartment was significantly inhibited by excess dipeptides. The kinetic parameters indicated that ceftibuten has higher affinity for the apical dipeptide transport system in the presence of a pH gradient, whereas it has much lower affinity for the basolateral dipeptide transport system at physiological pH of 7.4 than cephradine. These results suggest that both cephradine and ceftibuten are transported via the H+/dipeptide cotransport system localized in the apical membranes, and that the flux of these drugs across the basolateral membranes is also mediated by the dipeptide transport system in an H+ gradient-independent manner, exhibiting a rate-limiting step for their transcellular transport in Caco-2 monolayers.

Administration, Oral↗
PubMed1977

[Kinetic analysis of mechanisms of Na+-dependent organic acid transport in the proximal tubules of surviving frog kidney. II. Relationship between Na+ concentration in the medium and changes in the parameters of the Michaelis-Menten equation for fluorescein and uranin transport].

The dependence of active transport rates of fluorescein and uranin into proximal tubules was studied, firstly, on the concentration of these substrates in the incubation medium with constant Na-concentration and, secondly, on Na+-concentration in the medium with constant concentrations of fluorescein or uranin, Km, Vmax, and KmNa, VmaxNa values being determined correspondingly. With the decrease of Na+-concentration in the medium the apparent Km values for fluorescein and uranin increase, while Vmax values remain unchanged and ratios Vmax/Km decrease. The 1/Km value for uranin transport is a linear function of Na+-concentration, while it is a quadratic function of Na+-concentration for fluorescein transport. The KmNa value for fluorescein transport is twice as much as that for uranin transport. The obtained data suggest that one Na+-ion is spent from the medium for translocation of one uranin molecule across the basal membrane, whereas two Na+-ions from the medium are necessary for translocation of one fluorescein molecule. It is assumed that fluorescein and uranin transports are carried out by producing a four-fold transporting complex (a carrier+a substratum+2Na+; in the case of fluorescein 2Na+ appear from the medium, whereas in the case of uranin only one Na+ from the medium is used.

Animals↗
PubMed1998

Transport of L-valine-acyclovir via the oligopeptide transporter in the human intestinal cell line, Caco-2.

It has been reported that conjugating acyclovir, a potent antiviral with low oral bioavailability, to L-valine increases its urinary excretion in rats. However, it was also reported that this increase is not found for the D-valine ester, suggesting that a carrier-mediated mechanism is involved in its intestinal absorption. Therefore, mechanisms involved in the transepithelial transport of L-valine-acyclovir were investigated using the intestinal cell line, Caco-2, as a model system for the intestinal epithelium. Only the mucosal-to-serosal transport of acyclovir was increased by conjugation with L-valine (approximately 7-fold), suggesting the involvement of a carrier-mediated mechanism. This conclusion was supported by the finding that this increase was saturable. The mucosal-to-serosal transport of L-valine-acyclovir could be inhibited by L-glycylsarcosine, but not by L-valine, suggesting the involvement of the dipeptide carrier. Also it was found that L-valine-acyclovir inhibits the uptake of cephalexin, a substrate for the oligopeptide transporter. Stability of the esters in either the mucosal or serosal bathing solution is more than 90% after completion of the transport study. However, after transport, the receiver solution contained approximately 90% of acyclovir. Based on these findings it was concluded that absorption of the L-valine ester of acyclovir occurs as a result of uptake by the oligopeptide transporter at the apical cell membrane followed by intracellular hydrolysis of the ester and efflux of acyclovir.

Acyclovir↗
PubMed2001

Identification of differentiation-associated brain-specific phosphate transporter as a second vesicular glutamate transporter (VGLUT2).

Glutamate is the major excitatory neurotransmitter in mammalian CNS. In the presynaptic nerve terminal, glutamate is stored in synaptic vesicles and released by exocytosis. Previously, it has been shown that a transport protein originally identified as a brain-specific Na(+)-dependent inorganic phosphate transporter I (BNPI) functions as vesicular glutamate transporter and thus has been renamed VGLUT1. Recently, a protein highly homologous to VGLUT1, "differentiation-associated BNPI" (DNPI), has been discovered. Northern blot and in situ hybridization analyses indicate that DNPI mRNA is expressed in some brain regions in which VGLUT1 mRNA is not expressed. We now show that DNPI functions as vesicular glutamate transporter with properties very similar to VGLUT1 and propose to rename the protein VGLUT2. VGLUT2 is highly enriched in synaptic vesicles. Furthermore, VGLUT2 resides on a vesicle population that is distinct from vesicles containing the vesicular GABA transporter or VGLUT1, showing that the expression of VGLUT1 and VGLUT2 do not overlap. When VGLUT2 was expressed in BON cells, membrane fractions displayed ATP-dependent, carbonyl cyanide p-trifluoromethoxyphenylhydrazone-sensitive glutamate uptake. Overexpression of VGLUT2 in cultured autaptic GABAergic neurons yielded postsynaptic currents that were insensitive to the GABA(A) receptor antagonist bicuculline but blocked by the AMPA-receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfonyl-benzo[F]quinoxaline. Thus, expression of VGLUT2 suffices to cause GABAergic neurons to release glutamate in addition to GABA in a manner very similar to that reported previously for VGLUT1.

Animals↗
PubMed2006

Insulin restores glucose inhibition of adenosine transport by increasing the expression and activity of the equilibrative nucleoside transporter 2 in human umbilical vein endothelium.

L-Arginine transport and nitric oxide (NO) synthesis (L-arginine/NO pathway) are stimulated by insulin, adenosine or elevated extracellular D-glucose in human umbilical vein endothelial cells (HUVEC). Adenosine uptake via the human equilibrative nucleoside transporters 1 (hENT1) and 2 (hENT2) has been proposed as a mechanism regulating adenosine plasma concentration, and therefore its vascular effects in human umbilical veins. Thus, altered expression and/or activity of hENT1 or hENT2 could lead to abnormal physiological plasma adenosine level. We have characterized insulin effect on adenosine transport in HUVEC cultured in normal (5 mM) or high (25 mM) D-glucose. Insulin (1 nM) increased overall adenosine transport associated with higher hENT2-, but lower hENT1-mediated transport in normal D-glucose. Insulin increased hENT2 protein abundance in normal or high D-glucose, but reduced hENT1 protein abundance in normal D-glucose. Insulin did not alter the reduced hENT1 protein abundance, but blocked the reduced hENT1 and hENT2 mRNA expression induced by high D-glucose. Insulin effect on hENT1 mRNA expression in normal D-glucose was blocked by N(G)-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor) and mimicked by S-nitroso-N-acetyl-L,D-penicillamine (SNAP, NO donor). L-NAME did not block insulin effect on hENT2 expression. In conclusion, insulin stimulation of overall adenosine transport results from increased hENT2 expression and activity via a NO-independent mechanism. These findings could be important in hyperglycemia-associated pathological pregnancies, such as gestational diabetes, where plasma adenosine removal by the endothelium is reduced, a condition that could alter the blood flow from the placenta to the fetus affecting fetus growth and development.

Adenosine↗
PubMed1998

Determination of transport parameters of permeant substrates of the vesicular amine transporter.

Biological transport of moderately permeant compounds is obscured by diffusion of the compounds back across the membrane, so characterization of the transport of such compounds requires correction for permeability. A relatively simple method for determining kinetic parameters for moderately permeant compounds is presented here. After evaluating a compound's apparent permeability coefficient, its steady-state uptake is measured as a function of concentration. By comparing the concentration dependence of uptake measured both in the presence and in the absence of a complete inhibitor of the transporter, K(m) and Vmax for transport of that substrate may be calculated. When used to analyze transport of tyramine and hydroxyephedrine by the vesicular amine transporter, this method yields results consistent with other methods and with values for analogous impermeant substrates. In bovine adrenal chromaffin vesicles, tyramine and (-)erythro-hydroxyephedrine have apparent permeability coefficients of 4.7 +/- 1.0 x 10(-9) and 1.1 +/- 0.4 x 10(-8) cm/s, respectively. Values for K(m) are 15 +/- 9 and 34 +/- 14 microM and for Vmax are 1.3 +/- 0.2 and 1.4 +/- 0.9 nmol/min.mg of membrane protein, respectively.

Adrenal Medulla↗
PubMed1993

Tinkering with transporters: periplasmic binding protein-dependent maltose transport in E. coli.

Periplasmic binding protein-dependent transport systems represent a common mechanism for nutrient and ion uptake in bacteria. As a group, these systems are related to one another and to other transporters of both prokaryotes and eukaryotes, based on sequence similarity within an ATP-binding subunit and overall structural organization. These transporters probably all use energy derived from ATP to pump substrates across membranes. Although there is considerable information about the sequences and identity of the transporters, there is little information about how they work. That is, where do ligands bind? Where do the subunits or domains interact with one another? How is the energy of nucleotide binding and/or hydrolysis converted to conformational changes? In order to address these questions we have taken a genetic approach that involves studying mutant forms of a transporter. Rather than study mutations that result in complete loss of function, the study of mutations which perturb or alter the normal function of the transporter in a defined manner has provided a limited insight into how the answers to these questions may be obtained.

ATP-Binding Cassette Transporters↗
PubMed1996

Insulinomimetic effects of myricetin on lipogenesis and glucose transport in rat adipocytes but not glucose transport translocation.

Myricetin is a naturally occurring flavonol that is commonly found in tea, berries, fruits, and medicinal plants. It mimics insulin in stimulating lipogenesis and glucose transport in rat adipocytes in vitro. It was found to stimulate lipogenesis in rat adipocytes and enhance the stimulatory effect of insulin. The EC50 was estimated to be about 65 microM. Myricetin did not have any effect on insulin receptor autophosphorylation nor on the tyrosine kinase activity of the receptor. However, myricetin stimulated both D-glucose and D-3-O-methylglucose uptake in rat adipocytes. The Vmax of glucose transport was increased, but the Km did not change significantly. Immunoblot analysis of Glut4 in rat adipocyte plasma membrane showed that the stimulation of glucose transport was not a consequence of glucose transporter translocation. Instead, the stimulation in glucose uptake probably was due to a change in the intrinsic activity of the glucose transporter possibly caused by alterations in membrane fluidity or transporter-lipid interactions as a result of the insertion of myricetin into the membrane bilayer. Thus, myricetin may have therapeutic potential in the management of non-insulin-dependent diabetes mellitus by stimulating glucose uptake without the presence of fully functional insulin receptor.

3-O-Methylglucose↗
PubMed1994

Regulation of glucose transport and expression of GLUT3 transporters in human circulating mononuclear cells: studies in cells from insulin-dependent diabetic and nondiabetic individuals.

We have previously shown that human circulating mononuclear cells (CMCs) respond to physiological concentrations of insulin with a rapid increase in glucose transport rate. The responding cells were found to be the monocytes, and cells derived from individuals with insulin-dependent diabetes mellitus (IDDM) had lower basal and insulin-stimulated glucose transport rates. Of interest, both cell types were found to express the GLUT1 but not the typical insulin-responsive GLUT4 transporter isoform. To further study the mechanisms responsible for stimulation of transport in these cells, we investigated (1) the response to insulin-like growth factor-I (IGF-I) and insulin-mimetic agents, and (2) the expression of other glucose transporter isoforms in CMCs of nondiabetic and IDDM individuals. The time course of insulin-stimulated glucose uptake in CMCs was rapid, reaching a plateau within 30 minutes. CMCs showed a dose-dependent and highly sensitive increase in glucose uptake to IGF-I (maximal response reached at 0.1 to 0.5 nmol/L IGF-I). The IGF-I dose-response curve was similar for CMCs of control and IDDM individuals, but both the basal and maximal response to IGF-I were lower in the diabetic group (P < .01). CMCs did not respond to vanadate, lithium, hydrogen peroxide, or short incubation (1 hour) with metformin, but glucose uptake increased in response to peroxides of vanadate and longer-duration (14 hours) metformin incubations. The glucose transporter isoforms of separated monocytes and lymphocytes were further investigated by Northern blotting of total RNA with a GLUT3-specific cDNA probe and by Western blotting of total membranes using GLUT3-specific antiserum.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed2004

Glycine 154 of the equilibrative nucleoside transporter, hENT1, is important for nucleoside transport and for conferring sensitivity to the inhibitors nitrobenzylthioinosine, dipyridamole, and dilazep.

hENT1 and hENT2 are members of the human equilibrative nucleoside transporter family. hENT1 is ubiquitously expressed and plays an important role in the disposition and pharmacological activity of nucleoside drugs and nucleosides, such as adenosine. hENT2 is expressed in only a few tissues (e.g. muscle). hENT1 and hENT2 differ in their affinity for nucleoside substrates and in their sensitivity to inhibitors, such as nitrobenzylthioinosine (NBMPR). hENT1 has higher (or equal) affinity to hENT2 for all natural nucleosides except inosine. hENT1 is also more sensitive to NBMPR inhibition (IC50 approximately 0.4-8 nM) when compared with hENT2 (IC50 approximately 2.8 microM). This difference in inhibition potency is substantially dependent on the difference in amino acid at position 154 in hENT1 (glycine) and hENT2 (serine). Since NBMPR competitively inhibits nucleoside transporter activity, we hypothesized that G154 may also play a role in the transport of natural nucleosides and in the inhibition by other hENT1 inhibitors, dipyridamole (DP), and dilazep (DZ). Our results, using a yeast expression system, demonstrate that substituting glycine 154 of hENT1 with serine of hENT2 converts hENT1 to a transporter that exhibits partial characteristics of hENT2. For example, this conversion reduces sensitivity of hENT1 to the inhibitors NBMPR, DP, and DZ and reduces its transport affinity for the natural nucleosides cytidine and adenosine. However, this conversion renders hENT1 less sensitive to inhibition by anti-HIV drugs azidothymidine, dideoxyinosine, and the nucleobase, hypoxanthine. Collectively, these results suggest that glycine 154 plays an important role in the transport of nucleosides and in sensitivity to the inhibitors NBMPR, DP, and DZ.

Biological Transport↗
PubMed2003

The Escherichia coli outer membrane cobalamin transporter BtuB: structural analysis of calcium and substrate binding, and identification of orthologous transporters by sequence/structure conservation.

Gram-negative bacteria possess specialized active transport systems that function to transport organometallic cofactors or carriers, such as cobalamins, siderophores, and porphyrins, across their outer membranes. The primary components of each transport system are an outer membrane transporter and the energy-coupling protein TonB. In Escherichiacoli, the TonB-dependent outer membrane transporter BtuB carries out active transport of cobalamin (Cbl) substrates across its outer membrane. Cobalamins bind to BtuB with nanomolar affinity. Previous studies implicated calcium in high-affinity binding of cyanocobalamin (CN-Cbl) to BtuB. We previously solved four structures of BtuB or BtuB complexes: an apo-structure of a methionine-substitution mutant (used to obtain experimental phases by selenomethionine single-wavelength anomalous diffraction studies); an apo-structure of wild-type BtuB; a binary complex of calcium and wild-type BtuB; and a ternary complex of calcium, CN-Cbl and wild-type BtuB. We present an analysis of the binding of calcium in the binary and ternary complexes, and show that calcium coordination changes upon substrate binding. High-affinity CN-Cbl binding and calcium coordination are coupled. We also analyze the binding mode of CN-Cbl to BtuB, and compare and contrast this binding to that observed in other proteins that bind Cbl. BtuB binds CN-Cbl in a manner very different from Cbl-utilizing enzymes and the periplasmic Cbl binding protein BtuF. Homology searches of bacterial genomes, structural annotation based on the presence of conserved Cbl-binding residues identified by analysis of our BtuB structure, and detection of homologs of the periplasmic Cbl-binding binding protein BtuF enable identification of putative BtuB orthologs in enteric and non-enteric bacterial species.

Amino Acid Motifs↗
PubMed2005

Validation of in vitro cell models used in drug metabolism and transport studies; genotyping of cytochrome P450, phase II enzymes and drug transporter polymorphisms in the human hepatoma (HepG2), ovarian carcinoma (IGROV-1) and colon carcinoma (CaCo-2, LS180) cell lines.

Human cell lines are often used for in vitro biotransformation and transport studies of drugs. In vivo, genetic polymorphisms have been identified in drug-metabolizing enzymes and ABC-drug transporters leading to altered enzyme activity, or a change in the inducibility of these enzymes. These genetic polymorphisms could also influence the outcome of studies using human cell lines. Therefore, the aim of our study was to pharmacogenotype four cell lines frequently used in drug metabolism and transport studies, HepG2, IGROV-1, CaCo-2 and LS180, for genetic polymorphisms in biotransformation enzymes and drug transporters. The results indicate that, despite the presence of some genetic polymorphisms, no real effects influencing the activity of metabolizing enzymes or drug transporters in the investigated cell lines are expected. However, this characterization will be an aid in the interpretation of the results of biotransformation and transport studies using these in vitro cell models.

ATP Binding Cassette Transporter, Subfamily B, Mem↗