scholarly journals Absence of Rapid Exchange Component in a Low-Affinity Carrier Transport

1963 ◽  
Vol 46 (4) ◽  
pp. 721-731 ◽  
Author(s):  
Paul G. LeFevre ◽  
Keyword(s):  
Carrier Transport ◽  
Transport Model ◽  
Exchange Process ◽  
Tracer Uptake ◽  
Transport Systems ◽  
Human Red Blood Cells ◽  
Rapid Exchange ◽  
Carrier Mediated Transport ◽  
Net Uptake ◽  
High Concentrations

A previous study showed that human red blood cells equilibrate much less rapidly with D-glucose at moderately high concentrations than with C14-glucose added after the net movement is completed. This had been predicted from a simple reversible mobile-carrier mediated-transport model system suggested by the net monosaccharide transport kinetics in these cells, but is also consistent with the more complex models proposed for certain active transport systems to account for elevation of tracer fluxes of even low-affinity "substrates" when their trans-concentration is raised. The simple model predicts, however, that with any sugar showing a much lower apparent affinity for the reactive sites, such as D-ribose, this phenomenon would not be observed, and tracer equilibration should proceed at approximately the same rate as net uptake. The latter expectation was confirmed experimentally by analyses of the ribose, or radioactivity, content of washed red cells sampled serially during incubation with ribose or C14-ribose in the appropriate mixtures. The tracer ribose movement showed no evidence of a relatively rapid exchange component. The relative rapidity of glucose tracer uptake into cells preloaded with ordinary glucose may therefore more readily be attributed simply to depression of tracer efflux by competition for the saturated reactive sites, than to any action of the trans-concentration on the influx by way of a coupled exchange process.

scholarly journals Evidence for Carrier-Mediated Transport of Monosaccharides in the Ehrlich Ascites Tumor Cell

1967 ◽  
Vol 50 (7) ◽  
pp. 1907-1928 ◽  
Author(s):  
Alan R. Kolber ◽  
Paul G. LeFevre
Keyword(s):  
Transport Model ◽  
Ehrlich Ascites Tumor Cell ◽  
Tracer Uptake ◽  
Cell Suspensions ◽  
Ehrlich Ascites Tumor ◽  
Model Systems ◽  
Sugar Uptake ◽  
Ascites Tumor ◽  
Carrier Mediated Transport ◽  
Ehrlich Ascites

Evidence for carrier-mediated transport of monosaccharides in the Ehrlich ascites tumor cells was provided through kinetic analysis of data obtained by: (a) studying sugar uptake by dilute cell suspensions with an optical densimetric apparatus, (b) studying sugar uptake by thicker cell suspensions by means of direct chemical analytical methods using packed cell plugs, (c) observing the effects of a competitive inhibitor upon sugar uptake with the chemical analytical method, and (d) measurement of tracer uptake of a high affinity sugar in thick cell suspensions in the absence of net movement. Quantitative application of the data obtained with the above experimental procedures to theoretical model systems derived for both carrier-mediated transport and simple passive diffusion indicated that the results were consonant with predictions for the carrier-mediated transport model, but could not be explained on the basis of uncomplicated diffusion.

Transport of L-proline and alpha-methyl-D-glucoside by chicken proximal cecum during development

1991 ◽  
Vol 260 (3) ◽  
pp. G457-G463 ◽  
Author(s):  
M. Moreto ◽  
C. Amat ◽  
A. Puchal ◽  
R. K. Buddington ◽  
J. M. Planas
Keyword(s):  
Surface Area ◽  
Transport Systems ◽  
Independent System ◽  
Passive Components ◽  
Sugar Absorption ◽  
Carrier Mediated Transport ◽  
Lower Capacity ◽  
Nominal Surface ◽  
Passive Influx

We examined the characteristics of amino acid and sugar absorption by the proximal cecum (PC) of chickens during posthatch development. Rates of absorption of L-proline (Pro) and alpha-methyl-D-glucoside (MG) were measured at 2 days, 5 wk, and 13 wk after hatch with an in vitro everted-sleeve method. For each age, pieces of PC and midjejunum were incubated in solutions containing 0.1-50 mM Pro or MG, and the active and passive components of Pro and MG absorption were determined. Five conclusions may be stated. 1) There are two carrier-mediated transport systems for Pro in the PC: a higher capacity Na(+)-dependent system (Vmax between 1.6 and 3.2 nmol.mg-1.min-1), and a lower capacity Na(+)-independent system (Vmax 0.3-0.8 nmol.mg-1.min-1). 2) Whereas both Pro transport systems are present in the PC at 5 and 13 wk, only the Na(+)-dependent system was found at 2 days. Although rates of transport per milligram tissue by the Na(+)-dependent system fell during development, when rates were normalized to nominal surface area, Vmax was significantly higher in the 5-wk-old group than in the other groups. 3) MG transport is by a Na(+)-dependent system. Vmax values (nmol.mg-1.min-1) were 0.32 (2 days), less than 0.43 (5 wk), and = 0.55 (13 wk). These differences were not affected by normalization to surface area. 4) Because at physiological concentrations passive influx of Pro and MG would be negligible, absorption of amino acids and sugars by the PC would be dependent on the presence of carrier-mediated systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Space Charge Simulation of Electric Tree Before Germination in XLPE at DC Voltage Based on Improved Bipolar Carrier Transport Model

2021 ◽  
Author(s):  
Shiyou Wu ◽  
Shusheng Zheng ◽  
Aixu Zhong ◽  
Zongheng Zhang ◽  
Renjie Cao ◽  
...  
Keyword(s):  
Space Charge ◽  
Carrier Transport ◽  
Transport Model ◽  
Dc Voltage

Computational Carrier Transport Model of GNRFET

2019 ◽  
pp. 27-48
Author(s):  
Yaser M. Banadaki ◽  
Safura Sharifi
Keyword(s):  
Carrier Transport ◽  
Transport Model

Chloride transport by the cortical and outer medullary collecting duct

1987 ◽  
Vol 253 (2) ◽  
pp. F203-F212 ◽  
Author(s):  
V. L. Schuster ◽  
J. B. Stokes
Keyword(s):  
Chloride Transport ◽  
Collecting Duct ◽  
Exchange Process ◽  
Basolateral Membrane ◽  
Fine Tuning ◽  
Transport Systems ◽  
Acid Base ◽  
Intercalated Cell ◽  
Cl Channel ◽  
Collecting Tubule

The processes by which chloride is transported by the cortical and outer medullary collecting tubule have been most extensively studied using in vitro microperfusion of rabbit tubules. Chloride appears to be transported by three major mechanisms. First, Cl can be actively reabsorbed by an electroneutral Cl-HCO3 exchanger localized to the apical membrane of the HCO3-secreting (beta-type) intercalated cell. Cl exits this cell via a basolateral Cl channel. This anion exchange process can also operate in a Cl self-exchange mode, is stimulated acutely by beta-adrenergic agonists and cAMP, and is regulated chronically by in vivo acid-base status. Second, Cl can diffuse passively down electrochemical gradients via the paracellular pathway. Although this pathway does not appear to be selectively permeable to Cl, it is large enough to allow for significant passive reabsorption. Third, Cl undergoes recycling across the basolateral membrane of the H+-secreting (alpha-type) intercalated cell. HCO3 exit from this cell brings Cl into the cell via electroneutral Cl-HCO3 exchange; Cl then exits the cell via a Cl channel. Cl transport is thus required for acidification and alkalinization of the urine. Both of these processes exist in the cortical collecting tubule. Their simultaneous operation allows fine tuning of acid-base excretion. In addition, these transport systems, when functioning at equal rates, effect apparent electrogenic net Cl absorption without changing net HCO3 transport. These systems may play an important role in regulating Cl balance.

Carrier Transport Model for Lateralp-i-nPhotodiode in High-Frequency Operation

2005 ◽  
Vol 44 (4B) ◽  
pp. 2584-2585
Author(s):  
Kohkichi Konno ◽  
Osamu Matsushima ◽  
Kiyohito Hara ◽  
Gaku Suzuki ◽  
Dondee Navarro ◽  
...  
Keyword(s):  
High Frequency ◽  
Carrier Transport ◽  
Transport Model ◽  
High Frequency Operation

13C-NMR study of the inhibition of δ-chymotrypsin by a tripeptide-glyoxal inhibitor

2002 ◽  
Vol 362 (2) ◽  
pp. 339-347 ◽  
Author(s):  
Aleksandra DJURDJEVIC-PAHL ◽  
Chandralal HEWAGE ◽  
J. Paul G. MALTHOUSE
Keyword(s):  
13C Nmr ◽  
Exchange Process ◽  
Competitive Inhibitor ◽  
Minor Role ◽  
Oxyanion Hole ◽  
Inhibitor Complex ◽  
Rapid Exchange ◽  
Nmr Study ◽  
A Minor ◽  
Hydroxy Groups

A new inhibitor, Z-Ala-Pro-Phe-glyoxal (where Z is benzyloxycarbonyl),has been synthesized and shown to be a competitive inhibitor of δ-chymotrypsin, with a Ki of 25±8nM at pH7.0 and 25°C. Z-Ala-Pro-[1-13C]Phe-glyoxal and Z-Ala-Pro-[2-13C]Phe-glyoxal have been synthesized, and 13C-NMR has been used to determine how they interact with δ-chymotrypsin. Using Z-Ala-Pro-[2-13C]Phe-glyoxal we have detected a signal at 100.7p.p.m. which we assign to the tetrahedral adduct formed between the hydroxy group of Ser-195 and the 13C-enriched keto-carbon of the inhibitor. This signal is in a pH-dependent slow exchange with a signal at 107.6p.p.m. which depends on a pKa of ∼ 4.5, which we assign to oxyanion formation. Thus we are the first to detect an oxyanion pKa in a reversible chymotrypsin—inhibitor complex. A smaller titration shift of 100.7p.p.m. to 103.9p.p.m. with a pKa of ∼ 5.3 is also detected due to a rapid exchange process. This pKa is also detected with the Z-Ala-Pro-[1-13C]Phe-glyoxal inhibitor and gives a larger titration shift of 91.4p.p.m. to 97.3p.p.m., which we assign to the ionization of the hydrated aldehyde hydroxy groups of the enzyme-bound inhibitor. Protonation of the oxyanion in the oxyanion hole decreases the binding efficiency of the inhibitor. From this decrease in binding efficiency we estimate that oxyanion binding in the oxyanion hole reduces the oxyanion pKa by 1.3 pKa units. We calculate that the pKas of the oxyanions of the hemiketal and hydrated aldehyde moieties of the glyoxal inhibitor are both lowered by 6.4–6.9 pKa units on binding to chymotrypsin. Therefore we conclude that oxyanion binding in the oxyanion hole has only a minor role in decreasing the oxyanion pKa. We also investigate how the inhibitor breaks down at alkaline pH, and how it breaks down at neutral pH in the presence of chymotrypsin.

Taurine secretion in primary monolayer cultures of flounder renal epithelium: stimulation by low osmolality

2000 ◽  
Vol 279 (2) ◽  
pp. R704-R712 ◽  
Author(s):  
Siribhinya Benyajati ◽  
J. Larry Renfro
Keyword(s):  
Transport Systems ◽  
Disulfonic Acid ◽  
Renal Epithelium ◽  
Ussing Chambers ◽  
Monolayer Cultures ◽  
High Concentrations ◽  
The One ◽  
Secretory System ◽  
Taurine Efflux

Transepithelial taurine fluxes determined in short-circuited monolayer cultures of flounder renal proximal cells in Ussing chambers revealed net taurine secretion. Both unidirectional secretory and reabsorptive taurine fluxes exhibited saturation kinetics contributed by two distinct saturable transepithelial taurine transport systems operating at different taurine concentration ranges. The taurine secretory system operating below 0.5 mM had lower affinity but higher capacity than the reabsorptive system, whereas the one operating at high concentrations (0.5–3.0 mM) had higher affinity but the same capacity as the corresponding reabsorptive system. Exposure (2 h) of the cultures to hyposmotic medium in the presence of taurine increased taurine secretory flux twofold with no effect on the reabsorptive flux. The hyposmolality-induced increase in taurine secretion was associated with a decreased peritubular taurine efflux and a concurrent increased luminal taurine efflux; the latter occurred via a pathway that was not affected by 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid but inhibited by probenecid. The culture response in hyposmotic medium mimics the in vivo response of the intact marine fish kidney to dilution.

scholarly journals Snow-sourced bromine and its implications for polar tropospheric ozone

2010 ◽  
Vol 10 (16) ◽  
pp. 7763-7773 ◽  
Author(s):  
X. Yang ◽  
J. A. Pyle ◽  
R. A. Cox ◽  
N. Theys ◽  
M. Van Roozendael
Keyword(s):  
Tropospheric Ozone ◽  
Transport Model ◽  
Heterogeneous Reactions ◽  
Blowing Snow ◽  
Chemistry Transport Model ◽  
Sea Salt Aerosol ◽  
Catalytic Destruction ◽  
High Fraction ◽  
High Concentrations ◽  
Boundary Layer Ozone

Abstract. In the last two decades, significant depletion of boundary layer ozone (ozone depletion events, ODEs) has been observed in both Arctic and Antarctic spring. ODEs are attributed to catalytic destruction by bromine radicals (Br plus BrO), especially during bromine explosion events (BEs), when high concentrations of BrO periodically occur. However, neither the exact source of bromine nor the mechanism for sustaining the observed high BrO concentrations is completely understood. Here, by considering the production of sea salt aerosol from snow lying on sea ice during blowing snow events and the subsequent release of bromine, we successfully simulate the BEs using a global chemistry transport model. We find that heterogeneous reactions play an important role in sustaining a high fraction of the total inorganic bromine as BrO. We also find that emissions of bromine associated with blowing snow contribute significantly to BrO at mid-latitudes. Modeled tropospheric BrO columns generally compare well with the tropospheric BrO columns retrieved from the GOME satellite instrument (Global Ozone Monitoring Experiment). The additional blowing snow bromine source, identified here, reduces modeled high latitude lower tropospheric ozone amounts by up to an average 8% in polar spring.

Sign in / Sign up

Export Citation Format

Share Document