Net Efflux Rate Research Articles

Generalized whole-body Patlak parametric imaging for enhanced quantification in clinical PET

We recently developed a dynamic multi-bed PET data acquisition framework to translate the quantitative benefits of Patlak voxel-wise analysis to the domain of routine clinical whole-body (WB) imaging. The standard Patlak (sPatlak) linear graphical analysis assumes irreversible PET tracer uptake, ignoring the effect of FDG dephosphorylation, which has been suggested by a number of PET studies. In this work: (i) a non-linear generalized Patlak (gPatlak) model is utilized, including a net efflux rate constant kloss, and (ii) a hybrid (s/g)Patlak (hPatlak) imaging technique is introduced to enhance contrast to noise ratios (CNRs) of uptake rate Ki images. Representative set of kinetic parameter values and the XCAT phantom were employed to generate realistic 4D simulation PET data, and the proposed methods were additionally evaluated on 11 WB dynamic PET patient studies. Quantitative analysis on the simulated Ki images over 2 groups of regions-of-interest (ROIs), with low (ROI A) or high (ROI B) true kloss relative to Ki, suggested superior accuracy for gPatlak. Bias of sPatlak was found to be 16–18% and 20–40% poorer than gPatlak for ROIs A and B, respectively. By contrast, gPatlak exhibited, on average, 10% higher noise than sPatlak. Meanwhile, the bias and noise levels for hPatlak always ranged between the other two methods. In general, hPatlak was seen to outperform all methods in terms of target-to-background ratio (TBR) and CNR for all ROIs. Validation on patient datasets demonstrated clinical feasibility for all Patlak methods, while TBR and CNR evaluations confirmed our simulation findings, and suggested presence of non-negligible kloss reversibility in clinical data. As such, we recommend gPatlak for highly quantitative imaging tasks, while, for tasks emphasizing lesion detectability (e.g. TBR, CNR) over quantification, or for high levels of noise, hPatlak is instead preferred. Finally, gPatlak and hPatlak CNR was systematically higher compared to routine SUV values.

Estimation of the free [Ca2+] gradient across endoplasmic reticulum membranes by a null-point method.

The rate of unidirectional efflux of 45Ca from rat liver microsomal vesicles loaded with 45Ca and then treated with thapsigargin is not inhibited by increased [Ca2+] in the external medium, although the net efflux rate is substantially inhibited. We have used this property to measure the electrochemical gradient of Ca2+ from the inside to the outside of the vesicles at a series of Ca2+ loadings, by measuring the external [Ca2+]free at which there is zero net efflux. At a loading of 7.9 +/- 0.6 nmol/mg of microsomal protein, the apparent internal [Ca2+]free is 21 +/- 1.6 microM. As the loading is increased, the internal [Ca2+]free increases linearly up to a value of 47 +/- 3.6 microM at a loading of 21.6 +/- 1.6 nmol/mg. Using a similar technique, the value for [Ca2+]free in the endoplasmic reticulum of permeabilized L1210 cells was found to be 12.5 microM.

The type of dietary polyunsaturated fatty acids influences high density lipoprotein-mediated cholesterol efflux

We have examined the effects of dietary n−3 and n−6 polyunsaturated fatty acids on the composition of high density lipoproteins (HDL) in rabbits and on the ability of the HDL to promote cholesterol efflux from rabbit fibroblasts. We observed that HDL from rabbits fed MaxEPA oil contained significantly more unesterified cholesterol and cholesteryl ester than HDL from rabbits fed chow or chow plus safflower oil. The rate of net efflux of cholesterol from rabbit skin fibroblasts to medium containing HDL from animals fed chow plus MaxEPA oil was substantially greater than was seen when the medium contained HDL from rabbits fed chow alone or chow plus safflower oil. We suggest that the faster cholesterol efflux seen with HDL from animals fed MaxEPA oil supplements may account for some of the protection against coronary artery disease that has been reported for individuals consuming diets rich in marine mammals, fish or fish oils.

Influence of albumin on the net sinusoidal efflux of the organic anion dibromosulfophthalein from rat liver

Besides being excreted into bile, several anionic drugs and anionic drug conjugates are excreted from liver into plasma by a carrier-mediated process (sinusoidal efflux). In the study presented here, we investigated the influence of albumin on the net sinusoidal efflux of an organic anion from isolated perfused liver, with net sinusoidal efflux defined as the resultant of efflux and reuptake. We tested the hypothesis that albumin exerts its effect on net sinusoidal efflux through inhibition of repeat uptake rather than on the sinusoidal efflux process itself. We also studied possible acinar heterogeneity in net sinusoidal efflux rate of the organic anion. Isolated rat livers were preloaded with the nonmetabolizable anionic model compound dibromosulfophthalein in the absence (type I) or presence (type II) of bovine serum albumin. Fluorescence microscopy of dibromosulfophthalein in liver sections showed selective zone 1 loading after type I loading and homogeneous acinar distribution after type II loading. The rate of net sinusoidal efflux and biliary excretion was then studied in single-pass perfusions with various concentrations of bovine serum albumin in the medium. Net sinusoidal efflux of dibromosulfophthalein showed a marked dependence on albumin concentration in both type I and type II experiments. Net efflux rate reached a maximal value at a medium concentration of 300 mumol/L bovine serum albumin and was not increased further at 600 mumol/L. The initial uptake rate of dibromosulfophthalein was not significantly different in the 300 mumol/L and 600 mumol/L bovine serum albumin experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Some effects of hypoxia and medium ammonia enrichment on efflux rates and circulating levels of ammonia inNephrops norvegicus

Eutrophication has been reported for autumn months in regions of the Kattegat/Skagerrak, causing stress to bottom-living organisms. The present studies, undertaken in April (1989), investigated the effects of hypoxia and high ammonia levels in the burrowing decapodNephrops norvegicus (L.). The net ammonia efflux rates and circulating ammonia levels at 6 and 12°C, at normoxia [partial pressure of O2 in the water (torr),PwO2 = 155 torr)] and hypoxiaPwO2 = 24 torr) in normal seawater and ammonia-enriched (300µmol ammonia l−1) seawater were examined. The hourly weight-specific efflux rates were very variable and in all groups included some individuals which showed periods of no net efflux, or even a net uptake of ammonia. At each temperature, net efflux-rate differences due to treatments were not significant (P>0.05; ANOVA, in all cases) and only the differences between the net efflux rates of the normoxic groups were significantly affected by temperature (P<0.05; ANOVA). Circulating ammonia levels were also variable, and at 6°C the ammonia-enriched groups had significantly higher weight-specific blood ammonia content values than the normoxic group (P<0.05 in both cases). A net uptake of ammonia occurred in ammoniaenriched conditions — probably along a reversed NH4+ gradient, as downhill pNH3 gradients were maintained in all groups — and may represent the only means by which some branchial efflux of ammonia could proceed.

Total NFS pool and ammonia net efflux rate changes in Carcinus maenas during acclimation to low environmental salinity

1. 1. A significant decrease in the total NPS pool of Carcinus meanas L. was observed during acclimation to 26% seawater (8.5%. salinity) after transfer from 100% seawater (32%.). 2. 2. This fall was markedly slower than the related decrease in haemolymph osmolality. 3. 3. A rapid increase in ammonia net efflux rate followed the NPS pool decrease, reaching a maximum 2 days after transfer to the hypoosmotic salinity. 4. 4. The total ammonia release was less than expected from the NPS pool changes in the initial 2 days but a maintained, faster rate of net efflux, apparently unrelated to NPS changes, continued for at least 12 days. 5. 5. A marked decrease in haemolymph and urine ammonia concentration, and a rise in haemolymph NPS concentration, was observed during acclimation. 6. 6. The urinary component of the total ammonia net efflux was found to be negligible, in agreement with earlier findings in other species.

Proton Efflux from Roots of Intact Spergularia marina Plants

Despite numerous considerations of the importance of proton extrusion to plant mineral nutrition, measurements of net H+ efflux rates in photo-autotrophic plants growing in complete medium are rare, and the rates of efflux reported are considerably lower than that typical of low-salt seedlings. We present here the first report of short term net proton efflux from roots of a halophyte. and the highest rate of net efflux reported to date for any higher plant, in both low-salt and complete nutrient media. We also show responses of that efflux to a variety of treatments, including NaCl fusicoccin, shoot excision and darkness.

Cyclic GMP efflux from liver slices.

Cyclic GMP efflux from liver slices was studied when the intracellular cyclic GMP levels were elevated by incubation with N-methyl-N'-nitro-N-nitrosoguanidine (0.1 mM) and 3-isobutyl-1-methylxanthine (0.25 mM). A probenecid-sensitive and a probenecid-insensitive efflux system for cyclic GMP was found. It is suggested that the former system operates a carrier, which is saturable, the capacity of which is increased by alkylation with N-ethylmaleimide. The rate of net efflux of cyclic GMP increases 20-fold in the temperature interval 18-37 degrees C. Probenecid (0.5 mM) gives 50% inhibition of this system. The probenecid-insensitive cyclic GMP efflux component probably corresponds to passive diffusion. It appears that efflux may be an important complement to cyclic 3':5'-nucleotide phosphodiesterase activity in reducing intracellular cyclic GMP levels.

The mechanism of sugar uptake by sugarcane suspension cells

Sugarcane cell suspensions took up sugar from the medium at rates comparable to or greater than sugarcane tissue slices or plants in the field. This system offers an opportunity for the study of kinetic and energetic mechanisms of sugar transport in storage parenchyma-like cells in the absence of heterogeneity introduced by tissues. The following results were obtained: (a) The sugar uptake system was specific for hexoses; as previously proposed, sucrose was hydrolyzed by an extracellular invertase before the sugar moieties were taken up; no evidence for multiple sugar uptake systems was obtained. - (b) Uptake of the glucose-analog 3-O-methylglucose (3-OMG) reached a plateau value with an intracellular concentration higher than in the medium (approximately 15-fold). - (c) There was a balance of influx and efflux during steady state; the rate of exchange influx was lower than the rate of net influx; the Km value was higher (70 μM) than for net influx (24 μM); the exchange efflux is proposed to be mediated by the same transport system with a Km value of approximately 2.6 mM for internal 3-OMG; the rate of net efflux of hexoses was less than a third of the rate of exchange efflux. - (d) The uptake of hexoses proceeded as proton-symport with a stoichiometry of 0.87 H(+) per sugar; during the onset of hexose transport there was a K(+) exit of 0.94 K(+) per sugar for charge compensation. (It was assumed that the "real" stoichiometries are 1 H(+) and 1 K(+) per sugar.) The Km values for sugar transport and sugar-induced proton uptake were identical. Sucrose induced proton uptake only in the presence of cell wall invertase. - (e) There was no net proton uptake with 3-OMG by cells which were preloaded with glucose though there was significant sugar uptake. It is assumed, therefore, that the exit of hexose occurs together with protons. - (f) The protonmotive potential of sugarcane cells corresponded to about 120 mV: pH-gradient 1.1 units, membrane potential of-60 mV (these values increased if vacuolar pH and membrane potential were also considered). It was abolished by uncouplers, and the magnitude of the components depended on the external pH value. We present evidence for the operation of a proton-coupled sugar transport system in cell suspensions that were derived from, and have characteristics of, storage parenchyma. The quantitative rates of sugar transport suggest that the role of this transport system is not limiting for sugar storage.

Net efflux rate of norepinephrine from platelets in DOCA- and salt-treated rats

39 Wistar Kyoto rats were treated for 4 weeks with weekly injections of DOCA and extra sodium chloride in drinking water. The efflux rate of norepinephrine from platelets (k) was determined in 13 samples, each consisting of pooled blood from 3 animals. The efflux rate of norepinephrine was significantly higher (k=24.7±4.9) in these animals than in the 29 controls in which 10 k-determinations were made (k=17.0±4.5) (p<0.001). The heart weight was significantly higher in the DOCA-salt treated group and there was a significant correlation between heart weight and k (r9 p<0.05). As earlier studies have demonstrated a decrease in nonepinephrine in the granular fraction from heart tissue in DOCA-salt treated and hypertensive rats these findings suggest close similarities between norepinephrine storage in platelets and in neuronal cells.

The effect of substances releasing intracellular calcium ions on sodium-dependent calcium efflux from guinea-pig auricles.

1. 45-Ca efflux and resting tension were measured in isolated guinea-pig auricles under conditions known to change the intracellular free Ca ion concentration. 2. In the presence of [Na]o, caffeine (2mM) increases 45-Ca efflux, but does not produce a contracture, while in the absence of [Na]o and [Ca]o caffeine causes a contracture without increasing 45-Ca efflux. Adrenaline (10-minus5-10-minus 4M) with or without theophylline (0-5-1-0mM) has no effect on either 45-Ca efflux or resting tension. 3. In the presence of caffeine the rate of net efflux of Ca depends on [Na]o-2. Caffeine contractures of muscles in Na-free solution relax upon the addition of [Na]o. Relaxation is correlated with the increase in net efflux of Ca. 4. Cyanide (2mM) produces a variable increase in 45-Ca efflux without a concomitant contracture in Na-containing solutions, but in Na, Ca-free solutions a large contracture occurs without significant increase in 45-Ca efflux. 5. A large increase in 45-Ca efflux and a contracture were observed with the 'Ca-ionophore' X 537 A. 6. Changes in membrane potential (K-depolarization) in hypertonic solutions have no significant effect on Na-dependent 45-Ca efflux, which is an agreement with an electroneutral 2:1 Na-Ca exchange. 7. Cyanide and X 537 A both cause a considerable release of Ca ions from isolated guinea-pig heart mitochondria, while caffeine has no effect. 8. The results suggest a powerful role of the Na-Ca exchange system in reducing the intracellular Ca concentration after Ca release from intracellular stores.