The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform
Andrew S. Wechsler - One of the best experts on this subject based on the ideXlab platform.
-
Identification of Nucleoside Transport binding sites in the human myocardium.
Molecular and cellular biochemistry, 1998Co-Authors: Anwar-saad A. Abd-elfattah, Jeff Hoehner, Andrew S. WechslerAbstract:The role of Nucleoside Transport in ischemia-reperfusion injury and arrhythmias has been well documented in various animal models using selective blockers. However, clinical application of Nucleoside Transport inhibitors remains to be demonstrated in humans. It is not known whether human heart has Nucleoside Transport similar to that of animals. The aim of this study is to pharmacologically identify the presence of Nucleoside Transport binding sites in the human myocardium compared to animals. Myocardial tissue was obtained from guinea pig left and right ventricle, canine left ventricle, human intraoperative right atrium and human cadaveric right atrium and right and left ventricles. Myocardial preparations were obtained from tissue samples after homogenized and a differential centrifugation. Equilibrium binding assays were performed using [3H]-p-nitrobenzylthioinosine (NBMPR) at room temperature in the presence or absence of non-radioactive NBMPR or other Nucleoside Transport blockers such as p-nitrobenzylthioguanosine dipyridamole, lidoflazine, papaverin, adenosine and doxorubcine. From saturation curves and inhibition kinetics, we determined the relative maximal binding (Bmax) and dissociation constant (Kd) of [3H]-NBMPR binding of human myocardial preparations. Results demonstrated that the fresh human myocardial preparations have a specific binding site for NBMPR with a Bmax of 283+/-32 fmol/mg protein and Kd of 0.56+/-0.12 nM. These values are lower than those obtained from guinea pigs (Bmax = 1440+/-187 fmol/mg protein and Kd = 0.21+/-0.03 nM) and canine atrium (Bmax 594+/-73 fmol/mg protein, and Kd = 1.12+/-0.22 nM). Displacement kinetics studies revealed the relative potencies (of certain unrelated drugs as follow: p-nitrobenzylthioguanosine > dipyridamole > lidoflazine > pavaverine > Diltazam > adenosine > doxyrubicin. It is concluded that human myocardium contains an active Nucleoside Transport site which may play a crucial role in post-ischemic reperfusion-mediated injury in a wide spectrum of ischemic syndromes.
-
Identification of Nucleoside Transport binding sites in the human myocardium
Molecular and Cellular Biochemistry, 1998Co-Authors: Anwar-saad A. Abd-elfattah, Jeff Hoehner, Andrew S. WechslerAbstract:The role of Nucleoside Transport in ischemia-reperfusion injury and arrhythmias has been well documented in various animal models using selective blockers. However, clinical application of Nucleoside Transport inhibitors remains to be demonstrated in humans. It is not known whether human heart has Nucleoside Transport similar to that of animals. The aim of this study is to pharmacologically identify the presence of Nucleoside Transport binding sites in the human myocardium compared to animals.
-
Role of Nucleoside Transport and purine release in a rabbit model of myocardial stunning
Molecular and Cellular Biochemistry, 1998Co-Authors: Anwar S. Abd-elfattah, Ricky P. Maddox, Michael E. Jessen, Ivan M. Rebeyka, Andrew S. WechslerAbstract:Previously, we have demonstrated the role of Nucleoside Transport and purine release in post-ischemic reperfusion injury (myocardial stunning) in several canine models of ischemia. Since rabbits are deficient of xanthine oxidase, it is not known whether selective blockade of purine release is beneficial in a rabbit model of coronary artery occlusion and reperfusion (stunning). Therefore, we determined the hemodynamic and metabolic correlates in response to myocardial stunning in the presence or absence of selective Nucleoside Transport blocker (p-nitrobenzylthioinosine, NBMPR) and adenosine deaminase inhibitor (erythro-9-(2-hydroxy-3-nonyl)adenine, EHNA).
-
Role of Nucleoside Transport in Myocardial Injury and Protection: Separation Between Ischemic and Reperfusion Injury Using a Selective Nucleoside Transport Blocker, p-Nitrobenzylthioinosine, NBMPR
Developments in Cardiovascular Medicine, 1996Co-Authors: Anwar S. Abd-elfattah, Mohanad I. Shehab, Nashaat R. El-singaby, Andrew S. WechslerAbstract:Although ATP is a prerequisite energy source for ventricular function and cardiac metabolism, it is also a major source of inosine. Inosine is a precursor of free radical substrates utilized by endothelial xanthine oxidase (1,2). More than 90% of the ATP degraded during normothermic ischemia is retained inside the cardiomyocyte as inosine. During reperfusion and in the presence of molecular oxygen, inosine is released via a Nucleoside Transporter and rapidly converted to hypoxanthine and xanthine leading to generation of superoxide radicals (1–4) (Fig 1). Purines, oxypurines, free radical products and by-products are detected in the coronary sinus effluent collected during the first minute of reperfusion (5,6). Free radicals have been implicated in endothelial cell membrane injury and subsequent calcium entry, edema, neutrophil activation and infiltration and myocardial necrosis. Release of ATP catabolites is considered a sensitive index of ischemia (7,8). Since metabolic flux of purines during reperfusion is detrimental to coronary vasculature, we hypothesized that selective blockade of purine release by inhibiting Nucleoside Transport, before or after ischemia, would attenuate reperfusion-mediated ventricular and vascular stunning. Therefore, we investigated the role of myocardial ATP depletion and subsequent release of its catabolites via the Nucleoside Transport in the recovery of contractile function and attenuation of ventricular arrthythmias during reperfusion.
A R Paterson - One of the best experts on this subject based on the ideXlab platform.
-
sodium dependent Nucleoside Transport in mouse leukemia l1210 cells
Journal of Biological Chemistry, 1991Co-Authors: L Dagnino, L L Bennett, A R PatersonAbstract:Abstract Nucleoside permeation in L1210/AM cells is mediated by (a) equilibrative (facilitated diffusion) Transporters of two types and by (b) a concentrative Na(+)-dependent Transport system of low sensitivity to nitrobenzylthioinosine and dipyridamole, classical inhibitors of equilibrative Nucleoside Transport. In medium containing 10 microM dipyridamole and 20 microM adenosine, the equilibrative Nucleoside Transport systems of L1210/AM cells were substantially inhibited and the unimpaired activity of the Na(+)-dependent Nucleoside Transport system resulted in the cellular accumulation of free adenosine to 86 microM in 5 min, a concentration three times greater than the steady-state levels of adenosine achieved without dipyridamole. Uphill adenosine Transport was not observed when extracellular Na+ was replaced by Li+, K+, Cs+, or N-methyl-D-glucammonium ions, or after treatment of the cells with nystatin, a Na+ ionophore. These findings show that concentrative Nucleoside Transport activity in L1210/AM cells required an inward transmembrane Na+ gradient. Treatment of cells in sodium medium with 2 mM furosemide in the absence or presence of 2 mM ouabain inhibited Na(+)-dependent adenosine Transport by 50 and 75%, respectively. However, because treatment of cells with either agent in Na(+)-free medium decreased adenosine Transport by only 25%, part of this inhibition may be secondary to the effects of furosemide and ouabain on the ionic content of the cells. Substitution of extracellular Cl- by SO4(-2) or SCN- had no effect on the concentrative influx of adenosine.
Simon M. Jarvis - One of the best experts on this subject based on the ideXlab platform.
-
Chemical and Molecular Probes of Nucleoside Transport Mechanisms in Mammalian Tissues
Cell Membrane Transport, 1991Co-Authors: Simon M. JarvisAbstract:The passage of Nucleosides and synthetic Nucleoside analogues across plasma membranes of animal cells may occur by simple diffusion or more frequently by carrier-mediated processes. Two types of facilitated-diffusion Nucleoside Transporters that differ in their sensitivity to inhibition by nitrobenzylthioinosine (NBMPR) have been recognized (Jarvis and Young, 1987; Jarvis, 1988a; Plagemann et al., 1988). More recently, active Nucleoside Transport systems have been described in brush-border membrane vesicles and cells derived from renal and intestinal epithelia (Jarvis et al., 1989; Vijayalakshmi and Belt, 1988; Jakobs and Paterson, 1986). This article reviews results of recent studies of Nucleoside Transport in mammalian cells with particular emphasis on the methodologies employed in using chemical and molecular probes to explore the properties of Nucleoside Transporters.
-
multiple sodium dependent Nucleoside Transport systems in bovine renal brush border membrane vesicles
Biochemical Journal, 1991Co-Authors: Timothy C Williams, Simon M. JarvisAbstract:Na(+)-dependent Nucleoside Transport was examined in bovine renal brush-border membrane vesicles. Two separate Na+/Nucleoside coTransporters were shown to be present: (1) a system specific for purine Nucleosides and uridine, designated as the N1 carrier, and (2) an Na(+)-dependent Nucleoside Transporter that accepts pyrimidine Nucleosides, adenosine and analogues of adenosine, designated as the N2 system. Both systems exhibit a high affinity for Nucleosides (apparent Km values approximately 10 microM), are insensitive to inhibition by facilitated-diffusion Nucleoside Transport inhibitors, are rheogenic and exhibit a high specificity for Na+. Na+ increases the affinity of the influx of guanosine and thymidine, Nucleosides that serve as model permeants for the N1 and N2 Nucleoside Transporters respectively. The Na+/Nucleoside coupling stoichiometry is consistent with 1:1 for both carriers.
Alan R. P. Paterson - One of the best experts on this subject based on the ideXlab platform.
-
enhancement of retention and cytotoxicity of 2 chlorodeoxyadenosine in cultured human leukemic lymphoblasts by nitrobenzylthioinosine an inhibitor of equilibrative Nucleoside Transport
Leukemia, 2000Co-Authors: A M P Wright, Wendy P Gati, Alan R. P. PatersonAbstract:Enhancement of retention and cytotoxicity of 2-chlorodeoxyadenosine in cultured human leukemic lymphoblasts by nitrobenzylthioinosine, an inhibitor of equilibrative Nucleoside Transport
-
cloning and functional expression of a complementary dna encoding a mammalian Nucleoside Transport protein
Journal of Biological Chemistry, 1994Co-Authors: Qi Quan Huang, Carol E. Cass, Alan R. P. Paterson, Mabel W L Ritzel, James D YoungAbstract:Abstract Expression screening in Xenopus oocytes was used to isolate a cDNA from rat jejunal epithelium encoding a Na(+)-dependent Nucleoside Transport protein (named cNT1). The cDNA sequence of cNT1 predicts a protein of 648 amino acids (relative molecular mass 71,000) with 14 potential transmembrane domains. Data base searches indicate significant sequence similarity to the NUPC proton/Nucleoside symporter of Escherichia coli. There is no sequence similarity between cNT1 and proteins of mammalian origin. Functionally, cNT1 exhibited the Transport characteristics of the Nucleoside Transport system cit (selective for pyrimidine Nucleosides and adenosine) and accepted both 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC) as permeants (Km = 0.49 and 0.51 mM, respectively). The demonstration of Transport of AZT by cNT1 expressed in Xenopus oocytes provides the first direct evidence that AZT enters cells by Transporter-mediated processes, as well as by passive diffusion. Consistent with the tissue distribution of system cit Transport activity, transcripts for cNT1 were detected in kidney as well as jejunum. cNT1 therefore belongs to a potential new gene family and may be involved in the intestinal absorption and renal handling of pyrimidine Nucleoside analogs used to treat acquired immunodeficiency syndrome (AIDS).
-
Sodium-dependent Nucleoside Transport in rabbit intestinal epithelium.
Gastroenterology, 1991Co-Authors: Michael Roden, Alan R. P. Paterson, Klaus TurnheimAbstract:Abstract Cellular uptake of formycin B, a poorly metabolized analog of inosine, by the isolated epithelium of rabbit jejunum is three times higher in the presence of Na + than without this cation. The Na + -dependent Nucleoside Transport system is located in the apical membrane of the enterocytes and is capable of uphill Transport, as shown for formycin B and adenosine with brush border membrane vesicles. According to present and earlier evidence, Nucleoside Transport across the basolateral membrane appears to have the properties of facilitated diffusion. Na + -dependent formycin B Transport activity in intestinal epithelium decreases from jejunum to ileum and is absent in descending colon. As with Na + -coupled coTransport systems for other organic solutes, apical entry of formycin B is driven by the electrochemical Na + gradient into the cell. In contrast to the facilitated diffusion system for Nucleosides, Na + -dependent formycin B Transport is not inhibited by nitrobenzylthioinosine, but both carrier systems are sensitive to inhibitors of d-glucose Transport. Natural purine Nucleosides and uridine are strong inhibitors of Na + -dependent formycin B Transport. Trans-epithelial flux measurements substantiated that the Na + -dependent Transport mechanism for formycin B functions as an absorptive system.
L Dagnino - One of the best experts on this subject based on the ideXlab platform.
-
sodium dependent Nucleoside Transport in mouse leukemia l1210 cells
Journal of Biological Chemistry, 1991Co-Authors: L Dagnino, L L Bennett, A R PatersonAbstract:Abstract Nucleoside permeation in L1210/AM cells is mediated by (a) equilibrative (facilitated diffusion) Transporters of two types and by (b) a concentrative Na(+)-dependent Transport system of low sensitivity to nitrobenzylthioinosine and dipyridamole, classical inhibitors of equilibrative Nucleoside Transport. In medium containing 10 microM dipyridamole and 20 microM adenosine, the equilibrative Nucleoside Transport systems of L1210/AM cells were substantially inhibited and the unimpaired activity of the Na(+)-dependent Nucleoside Transport system resulted in the cellular accumulation of free adenosine to 86 microM in 5 min, a concentration three times greater than the steady-state levels of adenosine achieved without dipyridamole. Uphill adenosine Transport was not observed when extracellular Na+ was replaced by Li+, K+, Cs+, or N-methyl-D-glucammonium ions, or after treatment of the cells with nystatin, a Na+ ionophore. These findings show that concentrative Nucleoside Transport activity in L1210/AM cells required an inward transmembrane Na+ gradient. Treatment of cells in sodium medium with 2 mM furosemide in the absence or presence of 2 mM ouabain inhibited Na(+)-dependent adenosine Transport by 50 and 75%, respectively. However, because treatment of cells with either agent in Na(+)-free medium decreased adenosine Transport by only 25%, part of this inhibition may be secondary to the effects of furosemide and ouabain on the ionic content of the cells. Substitution of extracellular Cl- by SO4(-2) or SCN- had no effect on the concentrative influx of adenosine.
