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Biomedical subjects

J A Jacquez

Publications and source records attributed to J A Jacquez.

At least 37 records · Page 2Linked to original sources
PubMed1986

Different production and decay rates of six renin forms isolated from rat plasma.

Rat kidney contains six forms of renin, which are in different proportion from those found in plasma. We tested the hypothesis that differential removal and production of the forms might explain the differences between stored and circulating renins. In one group of rats, the six forms of renin were measured in plasma, 10 min after hemorrhage, or after aortic constriction. Plasma was run on an isoelectric focusing gel, and the six peaks of renin activity were expressed either as angiotensin I per hour per milliliter or as a percentage of the total plasma renin concentration. After hemorrhage or aortic constriction, the concentration of each form was significantly increased; the profile of circulating renin was significantly modified, showing an increase in proportion of form 2 and a decrease of forms 4, 5, and 6. In a second group, the disappearance of each form was measured 0 to 100 min after nephrectomy and fitted a two-exponential decay curve. Interpreted as a two-pool system with degradation from pool 1, the degradation rate decreased progressively, going from form 1 to 6. In a third group, arterial and renal venous blood were collected. The profile of secreted renin was calculated from the arterial venous difference. This profile fitted the prediction of the two-compartment model. Our data support the hypothesis that the proportion of each circulating renin form is the result of a balance between the rate of production of renin of constant composition and the degradation of the six forms at different rates.

Animals↗
PubMed1984

Red blood cell as glucose carrier: significance for placental and cerebral glucose transfer.

At plasma glucose values of 5 mM (90 mg/100 ml) the maximum glucose transport capacity of the human red cell membrane is 12,000 times the rate of glucose utilization by the red blood cell. Mammals, other than primates, that have been tested have a comparable high-capacity system during fetal life, which is lost soon after birth. It has been suggested that the availability of the water space of the red blood cell for distribution of glucose facilitates transfer across the placenta during fetal life in all mammals and across the blood-brain barrier in adult primates. Though plausible, more comparative studies of glucose transport in red blood cells of other species and direct experimental evaluations of the contribution of the red blood cell to glucose transfer across the placenta and the blood-brain barrier are needed.

Adult↗
PubMed1984

Modeling exchange in capillary beds.

Analysis of the handling of a material by the tissues of an organ after injection into the arterial inflow requires models of the functional units as well as of the distribution of the blood flow to the units. The major models of functional units are reviewed as are the effects of transit time distributions in the large vessels and capillaries. Multiple-indicator methods generally do not provide sufficient information to solve the inverse problem, i.e., to calculate the kinetics of handling the injected material in the tissue from the venous outflow curves. However, the use of simple, plausible assumptions allows one to extract considerable information from the venous outflow curves. These assumptions are 1) independence of the probability density functions of transit times for the arteries, veins, and capillaries, and 2) uniformity of handling of materials that do not leave the capillaries.

Animals↗
PubMed1983

Modulation of glucose transport in human red blood cells by ATP.

Depletion of energy stores of human red cells decreases the maximum transport capacity, Jm, for glucose transport to a value one-third or less of that found in red cells from freshly drawn blood. There is no change in Km. Hemolysis and resealing of red cells with ATP or ADP reverses the decrease in Jm. The maximum effect occurs at concentrations of ATP in the normal range for red cells, however, there is little effect from ADP concentrations in its normal range in freshly drawn red cells. Hemolysis and resealing with ATP gives an increase in Jm and an increase in differential labeling by photolytic labeling with tritiated cytochalasin B. Most of the activation is lost after a second hemolysis-reseal without ATP but about 25% of the activation remains.

Adenosine Diphosphate↗
PubMed1979

Studies on the turnover of proteins of the rat erythrocyte membrane.

The membrane proteins of erythrocytes were labeled by injecting L-[14C]-leucine and later L-[3H]leucine into rats, the two injections being 31 days apart. Control animals received the two isotopic forms of L-leucine simultaneously. Deviations in labeling ratio from control patterns were found on sodium dodecyl sulfate-polyacrylamide gel electrophorograms in restricted regions suggestive of turnover or loss of a few small proteins from the membrane between the 31 days. Most of the ghost proteins show no turnover.

Animals↗
PubMed1978

Comparison using central core model of renal medulla of the rabbit and rat.

The studies presented here use a central core model of the renal medulla, the details of which have been given elsewhere (Foster et al., Mathematical Biosci. 32: 307-335, 337-360, 1976). The central core model of the rabbit medulla predicts concentration gradients and volume flow rates in line with what is known for the rabbit. The handling of urea, however, is not consistent with the scheme proposed by Kokko and Rector (Kidney Intern. 2: 214-233, 1972). Moreover, the low concentration of urea predicted for the urine suggests an absence in the model of some form of mediated transport for urea in the inner medulla. The central core model of the rat medulla failed to predict results consistent with what is known about the rat. Substitution of the rabbit thermodynamic parameters into the model for the rat resulted in predictions that more closely resembled what one might expect, but were not entirely satisfactory. The implication is that there may be an interspecies difference in the concentration machinery between the rabbit and rat.

Animals↗
PubMed1978

Differential labeling of components in human erythrocyte membranes associated with the transport of glucose.

The irreversible inhibition of glucose transport by 1-fluoro-2,4-dinitrobenzene (FDNB) has been used to identify membrane proteins possibly associated with glucose transport in human erythrocytes. D-Glucose was shown to enhance significantly the rate of FDNB inhibition of transport when present during the reaction, whereas cytochalasin B (CB) and D-maltose retarded this FDNB inhibition of transport. This modulation of the inhibition reaction formed basis for a double isotopic differential labeling technique using [14C]- and [3H] FDNB followed by SDS-polyacrylamide gel electrophoresis to distinguish transport-associated polypeptides from bulk membrane dinitrophenylated proteins. Reactions in the presence of CB or maltose revealed the presence of a differentially labeled polypeptide(s), with a molecular weight of approximately 60,000-65,000 daltons. This effect could in part be reversed in the presence of D-glucose but not L-glucose. Reactions in the presence of D-glucose resulted in two regions of differential labeling. One region was around 200,000 daltons and the other corresponded to a 90,000-dalton band. Extraction of membrane proteins with p-chloromercuribenzene sulfonate resulted in no loss of the 60,000-dalton peak, indicating that this labeled polypeptide(s) was firmly anchored in the hydrophobic core of the membrane. These results indicate that as many as three membrane polypeptides are differentially labeled by FDNB under conditions strongly associated with the inhibition of the glucose transport system and may be involved in the regulation of glucose transport.

Biological Transport, Active↗
PubMed1976

An analysis of the adequacy of the asymmetric carrier model for sugar transport.

In 1972, Lieb, W. R. and Stein, W. D. (Biochim, Biophys. Acta 265, 187-207) in their review of sugar transport in human erythrocytes concluded that the conventional two-state carrier model was inconsistent with the experimental data available at that time. Since then, other papers have appeared which question the validity of the model. In this paper, we give a brief derivation of the equations describing the two-state carrier model, and analyze the predictions of the model in the classical experiments, i.e. zero-trans, infinite-cis, and equilibrium exchange. We show that the estimate of the half saturation constant of 2.8 mM for glucose at the inner face of the human red cell membrane for the infinite-cis procedure reported by Hankin, B.L., Liev, W.R. and Stein, W.D ((1972) Biochim. Biophys. Acta 288, 114-126) is unreliable. We note that all of the other experimental findings are consistent with the asymmetric carrier model.

Biological Transport, Active↗
PubMed1976

The action of a binary nonionic detergent on a kidney membrane fraction.

The disruption of a kidney cortex microsomal membrane preparation by a binary, nonionic detergent, was followed by using as markers, the changes in total protein content, and (Na+, K+)-ATPase in a supernatant fraction. Both markers responded similarly to changes in pH, microsome concentration and detergent concentration, but responded differently for time-dependent studies. The (Na+, K+)-ATPase activity was increased 2.2-fold (76.1 mumoles Pi/mg protein/h, 95% ouabain-sensitive) by a single detergent treatment and 3.5-fold (92% ouabain-sensitive) by a sequential detergent treatment. Changes in the critical micelle concentration (cmc) were observed for varying detergent and protein concentrations, which suggest interactions of monomeric detergent with the membrane. The peak of (Na+, K+)-ATPase activity occurred above the cmc which suggests the participation of micelles in releasing the enzyme from the membranes. Hill plots of the protein released as the detergent concentration was varied showed a change in the slope near the cmc indicating a four-fold increase in the binding of detergent to membranes as the detergent concentration is increased above the cmc. These results suggest that the disruption of membranes by detergent involves the binding of detergent monomers to the membrane followed by the formation of co-micelles of the detergent with segments of the membrane to complete the separation process.

Adenosine Triphosphatases↗
PubMed1975

One-way fluxes of alpha-aminoisobutyric acid in Ehrlich ascites tumor cells. Trans effects and effects of sodium and potassium.

One-way fluxes in the steady state and one-way influxes at zero intracellular concentrations were measured for alpha-aminoisobutyric acid (AIB) in Ehrlich ascites tumor cells at 32 degrees C. The one-way fulxes show trans effects in the concentration of AIB and are dependent on sodium levels. The one-way fluxes for initial influx and for the steady state were fitted with the equations derived for the frequently used two-state carrier model. Estimates of the parameters of these equations were obtained with use of nonlinear least squares. These gave relatively good fits of the flux data and the data on steady-state distribution ratios. The two-state carrier model predicted a trans inhibition of one-way influx and a trans stimulation of one-way efflux. The former phenomenon has been demonstrated for AIB transport in Ehrlich ascites cells and there is evidence, through less firm, for the latter.

Aminoisobutyric Acids↗
PubMed1975

Neutral amino acid transport pathways in uptake of L-thyroxine by Ehrlich ascites cells.

Neutral amino acid pathways were investigated as possible mediators of L-thyroxine (T4) entry into ascites cells. 14C-Labeled T4, alpha-aminoisobutyric acid (AIB), L-phenylalanine (Phe), and cycloleucine (cLeu) uptakes were measured at initial extracellular amino acid concentrations of 1 muM in a modified Krebs-Ringer phosphate buffer, pH 7.4. T4 uptake was markedly slower than that of AIB, Phe, or cLeu over a 25-min period. T4 uptake was neither competitively stimulated nor inhibited by either AIB or Phe when these latter amino acids were varied over the concentration range 1.0 x 10(-6) to 1.0 x 10(-2) M. Preloading cells with 30 mM L-methionine did not enhance the uptake of T4. TJ efflux from preloaded cells was not affected by either AIB or Phe in the extracellular fluid (ECF). The uptakes of AIB, Phe, and cLeu were markedly altered by replacement of ECF Na+ with choline+, whereas T4 uptake was unchanged. It was concluded that neural amino acid transport pathways (specifically A, L, ASC, and beta) do not participate in the transmembrane transfer of L-thyroxine into Ehrlich ascites cells.

Amino Acids↗