Transport of uridine in human red blood cells. Demonstration of a simple carrier-mediated process.

Cabantchik, Z. I.; Ginsburg, Hagaï

doi:10.1085/jgp.69.1.75

Cited by 87 publications

(31 citation statements)

References 23 publications

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“…The apparent Ki value for uridine inhibition of NBMPR binding to human erythrocyte membranes was 1-25 mmol/l at 25°C, a value higher than the apparent Km for uridine influx in intact cells (approximately 0-14 mmol/l at 25 0C, see Fig. 1) but close to the apparent Km of equilibrium exchange (1-3 mmol/l) (Cabantchik & Ginsburg, 1977;Shohami & Koren, 1979). The close similarity of the apparent Ki value for uridine inhibition of high-affinity NBMPR binding to the apparent Km value for uridine equilibrium exchange is further evidence that NBMPR competes directly with nucleosides for the permeation site of the transport system.…”

Section: Discussionmentioning

confidence: 70%

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Erythrocyte nucleoside transport: asymmetrical binding of nitrobenzylthioinosine to nucleoside permeation sites

Jarvis

McBride

Young

1982

The Journal of Physiology

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1. Nitrobenzylthioinosine is a potent and specific inhibitor of nucleoside translocation in animal cells. Kinetic and inhibitor binding studies were undertaken to clarify how this inhibitor interacts with the nucleoside transporter from human and nucleoside‐permeable type sheep erythrocytes. 2. [3H]nitrobenzylthioinosine inhibition of zero‐trans [U‐14C]uridine influx into nucleoside‐permeable type sheep cells was consistent with simple competitive inhibition (apparent Ki 1 nmol/l). Analysis of results using total inhibitor levels instead of cell‐free inhibitor concentrations did not affect the inhibition pattern, but increased the apparent Ki value by 5‐fold. 3. In contrast, [3H]nitrobenzylthioinosine was a non‐competitive inhibitor of zero‐trans [U‐14C]uridine efflux (apparent Ki 1·5 nmol/l). Dipyridamole, another potent inhibitor of nucleoside translocation, also inhibited zero‐trans [U‐14C]uridine influx in a competitive manner (apparent Ki 20‐40 nmol/l). 4. [3H]nitrobenzylthioinosine bound to high‐affinity sites on cell membranes from human and nucleoside‐permeable type sheep cells (apparent KD values ≃ 1 nmol/l). Binding of inhibitor to these sites was competitively blocked by uridine, a well characterized substrate for the nucleoside transporter (apparent Ki 1·25 and 0·9 mmol/l, respectively). These apparent Ki values are close to the apparent Km for uridine equilibrium exchange in human erythrocytes. 5. Similarly, deoxycytidine was found to be a competitive inhibitor of high‐affinity [3H]nitrobenzylthioinosine binding activity (apparent Ki 1·0 and 1·2 mmol/l for human and nucleoside‐permeable type sheep cell membranes, respectively). This contrasts with a previous report that this nucleoside had no effect on inhibitor binding activity. Transport studies confirmed that deoxycytidine is a substrate for the erythrocyte nucleoside transporter. Apparent Km and Vmax values for [U‐14C]‐deoxycytidine zero‐trans influx into human and nucleoside‐permeable type sheep cells were comparable to those obtained for [U‐14C]uridine. 6. It is suggested from these results that nitrobenzylthioinosine competes directly with nucleosides for the permeation site of the nucleoside transporter, but that inhibitor binds preferentially to the external membrane surface.

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Section: Discussionmentioning

confidence: 70%

“…Cabantchik & Ginsburg, 1977;Young, 1978;Jarvis & Young, 1980). Transport by this route in sheep cells was highly temperature dependent, with the Vmax for zerotrans influx about twice as sensitive to temperature (25-37 0C range) as the apparent Km.…”

Section: Discussionmentioning

confidence: 96%

Erythrocyte nucleoside transport: asymmetrical binding of nitrobenzylthioinosine to nucleoside permeation sites

Jarvis

McBride

Young

1982

The Journal of Physiology

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“…Rather like voltage clamp experiments that take membrane potential and channels to non-physiologicpotentials, the infinite-cis experiment reveals important insights into transporter function. The infinite-cis test yields experimental results that support the simple carrier hypothesis for uridine transport in red cells (83) and for GLUT4-mediated glucose transport in adipose(572). This establishes its utility and argues against specific technical problems in its application to red cell transport systems or to glucose transport systems in general.…”

Section: Transport Kineticsmentioning

confidence: 71%

Role of Monosaccharide Transport Proteins in Carbohydrate Assimilation, Distribution, Metabolism, and Homeostasis

Cura

Carruthers

2012

Comprehensive Physiology

138

117

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The facilitated diffusion of glucose, galactose, fructose, urate, myoinositol, and dehydroascorbic acid in mammals is catalyzed by a family of 14 monosaccharide transport proteins called GLUTs. These transporters may be divided into three classes according to sequence similarity and function/substrate specificity. GLUT1 appears to be highly expressed in glycolytically active cells and has been coopted in vitamin C auxotrophs to maintain the redox state of the blood through transport of dehydroascorbate. Several GLUTs are definitive glucose/galactose transporters, GLUT2 and GLUT5 are physiologically important fructose transporters, GLUT9 appears to be a urate transporter while GLUT13 is a proton/myoinositol cotransporter. The physiologic substrates of some GLUTs remain to be established. The GLUTs are expressed in a tissue specific manner where affinity, specificity, and capacity for substrate transport are paramount for tissue function. Although great strides have been made in characterizing GLUT‐catalyzed monosaccharide transport and mapping GLUT membrane topography and determinants of substrate specificity, a unifying model for GLUT structure and function remains elusive. The GLUTs play a major role in carbohydrate homeostasis and the redistribution of sugar‐derived carbons among the various organ systems. This is accomplished through a multiplicity of GLUT‐dependent glucose sensing and effector mechanisms that regulate monosaccharide ingestion, absorption, distribution, cellular transport and metabolism, and recovery/retention. Glucose transport and metabolism have coevolved in mammals to support cerebral glucose utilization. © 2012 American Physiological Society. Compr Physiol 2:863‐914, 2012.

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“…This allows the high-affinity transporter in group 5 cells to participate more fully in exchange reactions. By analogy with the kinetic behaviour of other transport systems (see Hoare, 1972a, b;Cabantchik & Ginsburg, 1977;and Naftalin & Holman, 1977, for examples), this approach towards equilibrium exchange conditions might be expected to increase both Km and Vmax for influx. As predicted by the simple carrier model of Lieb & Stein (1974) there was no significant difference in the mean Vmax/KKm ratio for system asc1 in group 4 versus group 5 horse erythrocytes.…”

Section: Discussionmentioning

confidence: 99%

Heterogeneity of amino acid transport in horse erythrocytes: a detailed kinetic analysis of inherited transport variation.

Fincham

Mason

Paterson

et al. 1987

The Journal of Physiology

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SUMMARY1. Thoroughbred horses were divisible into five distinct amino acid transport subgroups on the basis of their erythrocyte permeability to L-alanine, measured uptake rates ranging from 5 to 625 pmol 1 cells-' h-1 (0-2 mM-extracellular L-alanine, 37 0C).2. Erythrocytes from animals belonging to the lowest L-alanine permeability subgroup (5-15 /tmol 1 cells-' h-1) (transport-deficient type) exhibited slow nonsaturable transport of this amino acid. In contrast, cells from horses of the four transport-positive subgroups possessed additional high-affinity (apparent L-alanine Km (Michaelis constant) -03 mM) and/or low-affinity (apparent L-alanine Km -13 mM) Na+-independent transport routes selective for L-neutral amino acids of intermediate size. The two transporters, designated systems asc, and asc2, respectively, also possessed a significant affinity for dibasic amino acids.3. Amino acid transport activity in horse erythrocytes behaved as if controlled by three co-dominant alleles (s, h and 1), where s is a silent allele, and h and 1 code for the functional presence of systems ascl and asc2, respectively. 4. At physiological temperature, system asc, operated preferentially in an exchange mode. In contrast, system asc2 did not participate in exchange reactions at 37 0C, but did exhibit significant trans-acceleration at 25 'C.5. Reduction of the incubation temperature also resulted in dramatic decreases in apparent Km and Vmax for L-alanine uptake by system asc2, whereas the effects of temperature on system asc1 were much less marked. At 5 'C the two transporters exhibited equivalent kinetic constants for L-alanine influx. L-Alanine uptake by transport-deficient cells was relatively insensitive to temperature. Influx by this route may represent the ground-state permeability of the lipid bilayer.6. The effects of low temperature on system asc2 suggest a preferential impairment of the mobility of the unloaded carrier relative to that of the loaded transporter. Similarly, the different kinetic properties of systems asc1 and asc2 at physiological temperature are attributed to a difference in the mobilities of the empty carriers, this difference being minimized at 5 'C.

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Transport of uridine in human red blood cells. Demonstration of a simple carrier-mediated process.

Cited by 87 publications

References 23 publications

Erythrocyte nucleoside transport: asymmetrical binding of nitrobenzylthioinosine to nucleoside permeation sites

Erythrocyte nucleoside transport: asymmetrical binding of nitrobenzylthioinosine to nucleoside permeation sites

Role of Monosaccharide Transport Proteins in Carbohydrate Assimilation, Distribution, Metabolism, and Homeostasis

Heterogeneity of amino acid transport in horse erythrocytes: a detailed kinetic analysis of inherited transport variation.

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