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J C Ellory

Publications and source records attributed to J C Ellory.

At least 91 records · Page 5Linked to original sources
PubMed1991

Uridine transport in human erythrocytes: data from normal subjects and from patients with renal failure.

Erythrocyte uridine transport has been studied in eight normal individuals and eight patients on haemodialysis for chronic renal failure. The initial rate of zero-trans uridine influx at 37 degrees C has been measured as a function of extracellular uridine concentration using [14C]-labelled uridine. The results are consistent with Michaelis-Menten kinetics. In normal humans the mean Vmax for uridine influx was 32.8 +/- 6.4 mumol (1 cells)-1 s-1 (mean +/- S.D.) and the mean Km was 190 +/- 12.3 microM. The measurements made in renal failure patients were not significantly different (mean Vmax 30.1 +/- 7.1 mumol (1 cells)-1 s-1, mean Km, 185 +/- 13.2 microM). These results are discussed with reference to the reported data on uridine transport in human erythrocytes at temperatures between 4 and 35 degrees C; it is suggested that zero-trans uridine influx shows a decrease in temperature dependence above 25 degrees C. The Vmax for zero-trans uridine influx at 37 degrees C in normal erythrocytes represents a turnover number for the nucleoside transporter of 180 uridine molecules per second.

Adult↗
PubMed1991

The effects of cholesterol depletion on the sodium pump in human red cells.

Sodium pump function has been studied in human erythrocytes depleted of membrane cholesterol by incubation with phosphatidylcholine liposomes. The cells were sodium loaded by incubation in alkaline sodium phosphate and sodium pump activity was assessed by measurements of ouabain-sensitive 86Rb uptake at 37 degrees C. Cholesterol depletion had a biphasic effect; depletion by 5-25% increased sodium pump activity by a mean of 16.1% (S.D. 3.2%), whereas depletion by 35-50% decreased sodium pump activity by a mean of 14.8% (S.D. 3.8%). Cholesterol depletion had no reproducible effect on the ouabain-insensitive uptake of Rb. These results support the hypothesis that there may be an optimum membrane cholesterol content for sodium pump function.

Biological Transport, Active↗
PubMed1991

Effects of low ionic strength media on passive human red cell monovalent cation transport.

1. The effect of low ionic strength media on the residual, i.e. (ouabain + bumetanide + Ca2+)-insensitive, K+ influx was characterized in human red blood cells. 2. This K+ flux was enhanced significantly in isotonic solutions of low ionic strength using sucrose to maintain constant osmolarity. This effect was found for fresh red blood cells as well as for stored (bank) red blood cells. However, the absolute magnitude of K+ influx in solutions of low ionic strength was halved for stored red blood cells. 3. Anion replacement of Cl- by CH3SO4- did not affect residual K+ fluxes, showing that Cl- -dependent transport pathways (e.g. the KCl co-transporter) are not involved in the low ionic strength effect. 4. The enhanced K+ influx in low ionic strength media was reversible when the cells were resuspended in a solution of physiological ionic strength. 5. K+ influx measured in light and dense fractions of erythrocytes (separated by centrifugation and corresponding to samples enriched with either 'young' or 'mature' red cells) showed that the low ionic strength effect does not change markedly with cell age. 6. Low ionic strength media elevated residual, i.e. (ouabain + bumetanide + Ca2+)-insensitive, influx of both K+ and Na+ by about the same amount. In both cases the flux was linear with concentration in the range investigated (0.25-10 mM). No significant increase in the uptake of the cations Ca2+ and lysine in low ionic strength solutions could be found. 7. In CH3SO4- -containing solutions of physiological ionic strength the residual K+ influx was almost independent of cell volume, whereas this flux in CH3SO4- -containing solutions of low ionic strength declined as cell volume was increased. 8. K+ flux measurements in solutions of different external pH, where NaCl was replaced by sodium gluconate or sodium glucuronate, showed that the reduced ionic strength is of more importance for the enhanced residual K+ influx than the changed transmembrane potential or the changed intracellular pH. However, a small pH dependence could be found, the K+ flux passing through a minimum around pHi 7.3. 9. Hydrostatic pressure enhanced the residual K+ flux in media of low ionic strength synergistically, so that very large fluxes (greater than 10 mmol (1 cells)-1 h-1) were obtained at 40 MPa. The apparent activation volumes (delta V*) for the pressure-sensitive K+ flux were -108 and -69 ml mol-1 in low ionic strength or physiological ionic strength solutions respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Biological Transport↗
PubMed1991

Evidence for bumetanide-sensitive, Na(+)-dependent, partial Na-K-Cl co-transport in red blood cells of a primitive fish.

Tracer uptake studies identified the major routes for K+ transport in hagfish red cells, resolving them into ouabain-sensitive, loop diuretic-sensitive, and residual components. The K1/2 values for ouabain, bumetanide, and furosemide were 10(-5), 6 x 10(-7), and 5 x 10(-6) M, respectively. The properties of the Na-K-Cl co-transporter were investigated further by varying K+, Na+, and Cl- concentrations. The measured K1/2 values were similar to those for human red cells. Finally, the stoichiometry of Na:K:Cl uptake was determined, giving 1:1 for K+:Cl-; in contrast, no significant Na+ flux could be measured, although Na+ content must be present for measurable bumetanide-dependent K+ or Cl- flux to occur. The Na-K-Cl transport therefore shows Na(+)-dependent KCl co-transport or partial flux of the system.

Animals↗
PubMed1991

Modulation of Na-H antiporter activity in human lymphoblasts by altered membrane cholesterol.

The effects of changes in membrane cholesterol on Na-H antiporter activity in culture human lymphoblasts are described. Lymphoblast cholesterol alteration was achieved with liposomes of phosphatidylcholine (cholesterol depletion) or phosphatidylcholine plus cholesterol (cholesterol enrichment). Lymphoblast intracellular pH (pHi) was examined by fluorimetry using cells loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)5(6)-carboxyfluorescein, and the Na-dependent proton efflux rate at a pHi of 6.0 was taken as the maximum velocity of the Na-H antiporter. Lymphoblast membrane cholesterol depletion activated the Na-H antiporter, and enrichment of membrane cholesterol caused inhibition of the antiporter activity. This study demonstrates that in situ modification of membrane cholesterol can modulate the activity of the Na-H antiporter.

Carrier Proteins↗
PubMed1990

Characterization of peptide fluxes into human erythrocytes. A proton-n.m.r. study.

A new protocol for measuring cellular uptake of dipeptides was developed in which the problem of peptide hydrolysis is obviated by introduction into the cell suspension of a membrane-permeant peptidase inhibitor. The uptake of unlabelled dipeptide is readily monitored so long as some analytical technique is available for measuring the intracellular peptide concentration; in this study we used n.m.r. spectroscopy. Using this protocol, we demonstrated that dipeptide uptake by human erythrocytes occurs by simple diffusion through the lipid bilayer and not via a high-capacity protein-mediated transport system. Substantiating evidence includes demonstration that: (a) the fluxes are slow compared with known protein-mediated transport processes in human erythrocytes; (b) the uptake is not stereospecific; (c) the uptake does not display saturation kinetics; (d) the fluxes are significantly enhanced by butanol; (e) a distinct correlation exists between the size-corrected permeability coefficients of the dipeptides and their calculated n-octanol/water partition coefficients. It is calculated that under normal physiological conditions the diffusive fluxes of circulating plasma peptides into human erythrocytes are too small for these cells to play a significant role in dipeptide catabolism.

Anti-Bacterial Agents↗
PubMed1990

Selective inhibitors of KCl cotransport in human red cells.

Two analogues of the loop diuretics furosemide and bumetanide have been identified as differential inhibitors of KCl and NaKCl cotransport systems, assayed by measuring K+ influx in 'young' human red cells. H25 inhibited both NaKCl and KCl cotransport, with I50% values of 0.03 and 30 microM respectively; H74 had no effect on NaKCl cotransport, even at 0.3 mM, but inhibited KCl cotransport with an I50% of 75 microM. These compounds are therefore useful for resolving the two transport systems.

Anemia, Sickle Cell↗
PubMed1990

Factors affecting the activation and inactivation of KCl cotransport in 'young' human red cells.

KCl transport plays an important role in the control of 'young' red cell volume and hence MCHC. The activity of this pathway declines rapidly during maturation in vitro irrespective of whether the transporter is functioning or not. The presence of plasma retards the rate at which the transporter becomes cryptic; N-ethyl maleimide can restore transport activity. Low pH is more effective as an activator of the transporter than hypotonicity, suggesting that protons stimulate the transporter directly rather than via a change in cell volume.

Biological Transport↗
PubMed1989

Increased lysine transport capacity in erythrocytes from patients with chronic renal failure.

1. The initial rate of L-lysine influx into erythrocytes from 13 patients with chronic renal failure has been measured using 14C-labelled lysine. Ten patients were on maintenance haemodialysis and three had never been dialysed. The results are compared with data obtained from 12 normal individuals. 2. The rate of lysine influx into washed cells from buffered saline containing 0.02-0.5 mmol of L-lysine/l has been calculated. The results can be fitted with a model in which influx has a single saturable component obeying Michaelis-Menten kinetics, and a linear non-saturable component. 3. In uraemic erythrocytes the saturable component had a mean Vmax. of 0.762 mmol h-1 litre-1 of cells (n = 13, SEM 0.072) and a mean Km of 68.2 mumol/l (SEM 5.7). These values in normal erythrocytes were 0.566 mmol h-1 litre-1 of cells (n = 12, SEM 0.033) and 70.5 mumol/l (SEM 4.1), respectively. The mean apparent diffusion constant (KD) for the linear component of influx was 0.224 h-1 (SEM 0.039) in uraemic cells and 0.178 h-1 (SEM 0.028) in normals. 4. The 35% increase in mean Vmax seen in uraemic erythrocytes was statistically significant (P = 0.02). A similar increase in Vmax. in uraemic cells compared with controls was seen in erythrocytes which were studied in zero-trans conditions after depletion of intracellular amino acids. The mean values of Km and KD were not significantly different in uraemia. The origins of this increased membrane transport capacity for lysine in uraemia are discussed.

Adult↗
PubMed1989

Bepridil protects sickle cells against the adverse rheological effects of cyclical deoxygenation.

Calcium influx into sickle cells, with consequential activation of the Ca2(+)-activated K+ efflux (Gardos) channel, is a potential cause of cellular dehydration and loss of deformability. Bepridil, a recently described inhibitor of the Gardos channel, was found at pharmacological concentration (1 mumol/l) to inhibit significantly (P less than 0.01) the loss of deformability when sickle cells were subjected to cycles of oxygenation-deoxygenation for 15 h at 37 degrees C. Bepridil also inhibited significantly (P less than 0.005) the formation of irreversibly sickled cells. Drugs that preserve the K+ and therefore water content of erythrocytes are of potential value for hydrotherapy of sickle cell disease.

Anemia, Sickle Cell↗
PubMed1989

Effects of dialysis and transplantation on red cell Na pump function in renal failure.

Ion pumping by the erythrocyte Na, K-ATPase has been measured using ouabain-sensitive 86Rb flux in 11 non-dialysed patients with chronic renal failure (CRF), 13 patients on haemodialysis (HD), 13 patients on peritoneal dialysis (CAPD) and 15 patients with functional transplants (FT). Flux measurements were performed in plasma and simultaneous estimates of specific 3H-ouabain binding were made. The results indicate that, compared to normal controls, Na,K pump flux was reduced by 21% in CRF (p less than 0.01), 30% in HD (p less than 0.01), 15% in CAPD (p less than 0.02), and was normal in FT. Mean specific ouabain binding sites per cell (+/- SEM) were; controls 366 +/- 16; CRF, 290 +/- 16; HD, 344 +/- 17; CAPD, 321 +/- 18; FT, 345 +/- 26. Calculation of mean turnover rate per pump site indicated that patients on HD showed a 30% reduction compared to controls (influx 55 K ions/s versus 79 K ions/s, p less than 0.01). Cross-incubation experiments suggest that the lowered pump flux seen in the CRF and HD groups was due to plasma factors. This work shows that erythrocyte Na,K pump number is reduced in CRF, while patients on maintenance HD have normal pump numbers per erythrocyte but reduced pump turnover.

Adolescent↗
PubMed1989

Potassium transport in monkey erythrocytes.

K transport in Rhesus and Cynomolgus monkey erythrocytes has been characterised and compared to that in human erythrocytes. Transport due to the NaK pump, residual (diffusional) leak, volume-, pressure- and N-ethyl-maleimide-stimulated KCl system and internal Ca2+-stimulated K channel were similar to that in man but in the monkey it differed, in lacking the loop-diuretic-sensitive NaKCl cotransport system.

Animals↗
PubMed1988

The cross-linking reagent dimethyl suberimate modifies the target size of an insect nervous system nicotinic acetylcholine receptor.

Radiation inactivation and simple target theory were employed to determine the molecular weight of an insect CNS alpha-bungarotoxin binding component in the presence and absence of a cross-linking reagent, dimethyl suberimate. In the presence of the cross-linker, the number of binding sites decreased, and the apparent molecular weight (236,000) was approximately double the control value (112,000). This, together with sedimentation data, suggests that the lower value represents only a portion of the insect nicotinic receptor molecule. A model is presented to account for the increase in target size and reduction in the number of alpha-[3H]bungarotoxin binding sites in the presence of dimethyl suberimate.

Animals↗