Biomedical subjects

N Harvey

Publications and source records attributed to N Harvey.

17 recordsLinked to original sources

PubMed1992

Renal Na(+)-phosphate cotransport in X-linked Hyp mice responds appropriately to Na+ gradient, membrane potential, and pH.

To investigate the mechanism for the 50% decrease in Vmax of the high-affinity phosphate transport system in the renal brush-border membrane of X-linked Hyp mice, we compared the effects of external Na+ concentration, membrane potential, pH, phosphonoformic acid (PFA), and arsenate on Na(+)-Pi cotransport in brush-border membrane vesicles prepared from normal mice and Hyp littermates. The affinity of the Na(+)-Pi cotransport system for Na+ (apparent Km = 60 +/- 7 and 64 +/- 2 mM for normal and Hyp mice, respectively) and the Na(+)-Pi stoichiometry estimated from Hill plots (2.5 +/- 0.2 and 2.9 +/- 0.6 for normal and Hyp mice, respectively) were similar in brush-border membranes of both strains. Inside-negative membrane potential, generated by anions of different permeabilities, stimulated Na(+)-Pi cotransport and inside-positive membrane potential generated by valinomycin, and a K+ gradient (outside greater than inside) inhibited Na(+)-Pi cotransport to the same extent in brush-border membranes derived from normal mice and Hyp littermates. The pH dependence of Na(+)-Pi cotransport was similar in brush-border membrane vesicles of normal and Hyp mice. The ratio of Na(+)-Pi cotransport measured at pH 7.5 relative to that at pH 6.5 was 2.9 +/- 0.6 in normal mice and 2.9 +/- 0.7 in Hyp mice. PFA was a competitive inhibitor of Na(+)-Pi cotransport in brush-border membranes of both normal and Hyp mice. However, the apparent Ki for PFA was significantly lower in Hyp mice (0.31 +/- 0.01 and 0.19 +/- 0.02 mM in normal and Hyp mice, respectively, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Wishful thinking impairs belief-desire reasoning: a case of decoupling failure in adults?

Subjects were presented with a scenario that described how a certain type of opinion poll can be manipulated by respondents to put one particular political party (the threatened party) at a disadvantage. In a first experiment, people supporting this party but pretending to oppose it were found to be as likely to say that they would manipulate the poll as people who actually opposed it. In a second experiment, the threat embodied in the scenario was made more direct. It was also more salient because the study was carried out at a time of heightened political awareness when supporters of the threatened party were genuinely concerned about its future. People supporting the threatened party but pretending to oppose it were now about half as likely to say that they would manipulate the poll as those who actually opposed it. Two explanations for this breakdown in the belief-desire reasoning subserving pretense are considered.

Adolescent↗

PubMed1991

Renal brush-border membrane Na(+)-sulfate cotransport: stimulation by thyroid hormone.

The present study was undertaken to examine the interaction of phosphonoformic acid (PFA) with the Na(+)-sulfate cotransporter and the effect of thyroid hormone (triiodothyronine; T3) on Na(+)-dependent sulfate transport and Na(+)-dependent PFA binding in mouse renal brush-border membrane vesicles. PFA inhibits Na(+)-dependent sulfate transport in a competitive manner [apparent inhibitory constant (Ki) = 4.3 +/- 1.1 mM]. T3 administered in pharmacological doses significantly stimulates Na(+)-dependent sulfate transport in renal brush-border membranes compared with vehicle-treated controls. Although T3 has no effect on Na(+)-dependent glucose transport, T3 also stimulates Na(+)-dependent phosphate transport. Kinetic studies demonstrate that T3 increases the apparent maximal velocity (Vmax) for Na(+)-sulfate cotransport without changing the apparent Michaelis constant (Km). T3 does not significantly affect either Na(+)-dependent PFA binding or the phosphate- and sulfate-displaceable components of Na(+)-dependent PFA binding. Finally, Na(+)-dependent brush-border membrane sulfate transport is unchanged in phosphate-deprived mice that exhibit increased Na(+)-phosphate cotransport and in X-linked Hyp mice that exhibit impaired Na(+)-phosphate cotransport. The present results demonstrate that 1) PFA is a competitive inhibitor of Na(+)-sulfate cotransport, 2) T3 stimulates Na(+)-dependent sulfate, as well as Na(+)-dependent phosphate transport, but has no effect on PFA binding, and 3) phosphate deprivation and the X-linked Hyp mutation do not influence Na(+)-sulfate cotransport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Major histocompatibility complex antigen expression on lymphocytes from aging strain A mice.

Molecules encoded by the major histocompatibility complex (MHC) are crucial for the proper functioning of the immune response. In this study, the levels of class I and class II major histocompatibility antigens on lymphocytes from strain A mice were measured as a function of age. Class I protein levels increased significantly on both peripheral blood and spleen (T cells and B cells) lymphocytes with age. This increase in MHC class I protein levels was accompanied by an increase in class I mRNA levels. On the other hand, class II protein levels did not show a significant change with age. Moreover, while the percentage of class I-expressing spleen lymphocytes stayed at a steady-state level of 100% with age, the percentage of class II-expressing spleen lymphocytes decreased from 85% in young animals to 70% in old animals. This decrease was due to a decrease in the relative proportion of B cells compared to T cells in the spleen lymphocyte population of old mice. When class II mRNA levels were measured, it was found that these levels decreased markedly with age. Overall, it is clear that the regulation of MHC class I and class II expression changes with age in A strain mice. Since optimal levels of MHC expression are crucial for the proper functioning of cellular and humoral immune responses, it will be most interesting to understand how the control of MHC gene expression changes with age and whether MHC gene expression can be modulated in old individuals to restore better immune function.

Aging↗

PubMed1990

Normal molecular size of the Na(+)-phosphate cotransporter and normal Na(+)-dependent binding of phosphonoformic acid in renal brush border membranes of X-linked Hyp mice.

X-linked Hyp mice have a specific defect in Na(+)-dependent phosphate (Pi) transport at the renal brush border membrane (BBM). In the present study we examined the effect of the Hyp mutation on the molecular size of the Pi transporting unit and on Na(+)-dependent 14C-phosphonoformic (PFA) binding in renal BBM vesicles. By radiation inactivation analysis, we demonstrated that the molecular size of the Na(+)-Pi cotransporter is similar in normal (242 +/- 16 kDa) and Hyp mice (227 +/- 39 kDa). Moreover, while BBM Na(+)-dependent Pi transport is significantly reduced in Hyp mice (249 +/- 54 vs 465 +/- 82 pmol/mg protein/6s), genotype differences in (1) Na(+)-dependent PFA binding (1020 +/- 115 vs 1009 +/- 97 pmol/mg protein/30 min), (2) Pi-displaceable Na(+)-dependent PFA binding (605 +/- 82 vs 624 +/- 65 pmol/mg protein/6s), and (3) phosphate uptake at Na(+)-equilibrium (67 +/- 10 vs 54 +/- 7 pmol/mg protein/6s) are not apparent. The present data demonstrate that the molecular size of the renal BBM Na(+)-Pi cotransporter is normal in Hyp mice and suggest that the number of Na(+)-Pi cotransporters may not be reduced in the mutant strain.

Animals↗

PubMed1988

The 'worried well'.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗

PubMed1988

Stereoselective recognition in phospholipid monolayers.

During the past ten years we have investigated the stereochemistry of intermolecular interactions in monolayers at the air-water interface, a field which has never been developed explicitly before to our knowledge. Although we demonstrated clear enantiomeric and diastereomeric interactions for a number of chiral surfactants, we found no evidence whatsoever for stereoselective interaction in dipalmitoylphosphatidylcholine (DPPC) monolayers or vesicles by standard monolayer techniques, differential scanning calorimetry or ultra-highfield NMR. The present article extends these observations to dimyristoyl- and dilauroylphosphatidylcholine. Results from dynamic surface tension studies are also reported. In no case could chiral recognition be demonstrated using the 95% confidence limit as the criterion. In our previous study of DPPC mixtures with another chiral surfactant the question arose as to whether chiral interactions could be transmitted through intervening phospholipid molecules. This question is addressed by examining the force-area curves for a variety of mixed monolayers composed of chiral surfactants and phospholipids. We conclude that the chiral discrimination observed in some of these mixed monolayers is due to the direct interaction of chiral centers, and not due to the transmission of chirality from one stereocenter to the next through intermediate achiral molecules. Finally, we will consider the question of why phospholipids, the most ubiquitous of natural chiral surfactants, should show so little chiral discrimination in view of the wide occurrence of high stereoselectivity in many natural processes.

Dimyristoylphosphatidylcholine↗

PubMed1986

No phospholipid monolayer-sugar interactions.

Studies by a number of workers using the Langmuir film balance have shown that when carbohydrates, such as sucrose or glycerol, are dissolved in a subphase on which a phospholipid is spread, film expansion occurs (Cadenhead & Demchak, 1969; Cadenhead & Bean, 1972; Maggio et al., 1976; Maggio & Lucy, 1978). Recently such effects have been observed again, particularly with the carbohydrates galactose and trehalose (Johnston et al., 1984). The origin of these film expansions was uncertain, and various suggestions have been made to explain them. One idea was that they might be due to interactions which these carbohydrates have with the water molecules close to the polar head groups of the lipids. Recent studies in our two laboratories, described here, show that the magnitude of the expansion effects is variable and that in general they arise from surfactant impurities in the sugars. These impurities are observed in carbohydrates which are reputedly of high grade; the amount of impurity present can vary from batch to batch, and sometimes they can be difficult to remove. Film balance techniques or subphase preparation can mask the detection of minor impurities. The presence of surfactant impurities in reputedly pure carbohydrates needs to be considered in other biochemical and biophysical studies of lipids and cell membranes.

Carbohydrates↗

PubMed1983