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Biomedical subjects

A J Williams

Publications and source records attributed to A J Williams.

At least 19 recordsLinked to original sources
PubMed1992

Functional analysis of the human vascular cell adhesion molecule 1 promoter.

The vascular cell adhesion molecule 1 (VCAM-1) is a 110-kD member of the immunoglobulin gene superfamily expressed on the surface of interleukin 1 beta- or tumor necrosis factor alpha (TNF)-stimulated endothelial cells. The cell surface protein functions as an inducible adhesion receptor for circulating mononuclear leukocytes and some tumor cells. We have previously characterized the genomic organization of the VCAM1 gene and described its chromosomal localization. In this report, the promoter of the VCAM1 gene is characterized. New transcription of the VCAM1 gene occurred when endothelial cells were treated with TNF. Fusion plasmids containing the 5' flanking sequence of the VCAM1 gene and the chloramphenicol acetyltransferase reporter gene were used to identify cis-acting sequences that direct the cytokine-induced transcription. When transfected into bovine aortic endothelial cells, constructs containing 755 bp of the 5' flanking sequence were induced by TNF. Within the cytokine-responsive region of the core promoter were functional NF-kappa B and GATA elements. Upstream of the core promoter, the VCAM1 5' flanking sequence contained a negative regulatory activity. NF-kappa B-mediated activation of VCAM1 gene expression may lead to endothelial expression of a mononuclear leukocyte adhesion molecule associated with initial events in the development of an atherosclerotic lesion.

Animals↗
PubMed1992

Nucleotide sequence of rat vascular cell adhesion molecule-1 cDNA.

Vascular cell adhesion molecule 1 (VCAM-1) is an inducible transmembrane protein which is expressed by vascular endothelium following cytokine activation. VCAM-1 mediated the adhesion of certain blood leukocytes and tumor cells via the interaction with its counter-receptor, the integrin VLA4. When initially cloned from interleukin-1 (IL-1) stimulated human umbilical vein endothelial cells, VCAM-1 was reported to contain six immunoglobulin-like domains. However, subsequent cDNA clones and structural analysis of the human gene evealed an alternatively spliced seventh immunoglobulin domain. This seven domain form appears to be the predominant transcript in IL-1 activated endothelium. In this report, the cloning and nucleotide sequence of rat VCAM-1 is described.

Amino Acid Sequence↗
PubMed1992

The polymorphic photopigments of the marmoset: spectral tuning and genetic basis.

The marmoset (Callithrix jacchus jacchus), a South American monkey, is polymorphic for the middle- to long-wave cone photopigments: the three variant pigments have spectral peaks at 543, 556 and 563 nm. Comparisons of the deduced amino acid sequences of these pigments indicate that the variations in spectral sensitivity are associated with the presence or absence of hydroxyl-bearing residues at sites 180 and 285; but, in contrast to the additive hypothesis of Neitz et al. (1991), we propose that adjustments at site 233 may also be required to produce viable long-wave and middle-wave pigments. Within a family group of monkeys, we find that a restriction site polymorphism in the photopigment gene segregates in a way that is consistent with the single X-linked gene hypothesis previously proposed on the basis of the photopigment types present in male and female marmosets.

Amino Acid Sequence↗
PubMed1992

The calcium-release channel from cardiac sarcoplasmic reticulum: function in the failing and acutely ischaemic heart.

Junctional SR membrane vesicles have been isolated from chronically failing human hearts explanted at transplant operations. Vesicles have been incorporated into artificial planar phospholipid bilayers and the activity of single calcium-release channels investigated under voltage-clamp conditions. The properties of these channels are similar to those previously reported from normal animal tissue and do not provide evidence that the function of individual calcium-release channels is altered in the failing heart. Using radio-labelled ryanodine binding as a specific marker for the calcium-release channel, we demonstrate that, in the sheep heart, ischaemia results in the degradation of the calcium-release channel. The activation of proteases and oxidant stress in the ischaemic and re-perfused post-ischaemic myocardium are likely mediators of cell injury. Using the protease trypsin and the photosensitisation of rose bengal to generate the reactive oxygen species (ROS) singlet oxygen and superoxide radicals we demonstrate a direct effect on the calcium-release channel in vitro. Exposure of junctional SR vesicles to trypsin or oxidant stress resulted in the progressive loss of specific ryanodine binding and the degradation of high molecular weight proteins identified by polyacrylamide gel electrophoresis. The activity of single channels was also modified during exposure to proteolysis or oxidant stress; an initial increase in channel opening was observed followed by irreversible loss of channel function. Degradation of specific proteins, such as the calcium-release channel, may contribute to contractile dysfunction in the ischaemic and reperfused post-ischaemic myocardium.

Adult↗
PubMed1992

Modification of gating of an airway epithelial chloride channel by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB).

5-Nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) has been shown to produce a reduction in channel open probability in a number of epithelial chloride channels. We have investigated its action on a calcium-dependent airway epithelial chloride channel, which shows voltage-dependent gating following incorporation into planar phospholipid bilayers. Since the channel demonstrates a distinct subconductance state at approximately one-third of the fully open level, both 50 and 20% threshold analysis (TA) have been used to describe channel kinetics. Lifetime analysis using 50% TA in the absence of NPPB showed that two open and three closed lifetimes provided the optimal fit. Similar analysis using 20% TA required only two closed lifetimes and allowed for tentative assignment of tau values to either substate or fully closed events. NPPB (10-100 microM) produced a concentration-related shift of the normal voltage dependence of gating, with more negative holding potentials being required to produce a given channel open probability than in the absence of NPPB. Ten microM NPPB produced a similar shift in lifetime values. However, addition of 50 microM NPPB produced a unique, single open lifetime. No evidence was found for NPPB acting as a direct voltage-dependent blocker of chloride conductance.

Animals↗
PubMed1992

Block of the sheep cardiac sarcoplasmic reticulum Ca(2+)-release channel by tetra-alkyl ammonium cations.

The purified ryanodine receptor channel of the sheep cardiac muscle sarcoplasmic reticulum (SR) membrane functions as a calcium-activated cation-selective channel under voltage-clamp conditions following reconstitution into planar phospholipid bilayers. We have investigated the effects of the tetra-alkyl ammonium (TAA) cations, (CnH2n+1)4N+ and the trimethyl ammonium cations, ethyltrimethyl ammonium and propyltrimethyl ammonium, on potassium conductance through the receptor channel. Small TAA cations (n = 1-3) and the trimethyl ammonium derivatives act as asymmetric, voltage-dependent blockers of potassium current. Quantitative analysis of the voltage dependence of block indicates that the conduction pathway of the sheep cardiac SR ryanodine receptor channel contains two distinct sites for the interaction of these small organic cations. Sites are located at approximately 50% for tetramethyl ammonium (TMA+) and 90% for tetraethyl ammonium (TEA+) and tetrapropyl ammonium (TPrA+) of the voltage drop across the channel from the cytosolic face of the protein. The chemical substitution of an ethyl or propyl group for one of the methyl groups in TMA+ increases the voltage dependence of block to a level similar to that of TEA+ and TPrA+. The zero-voltage dissociation constant (Kb(0)) falls with the increasing number of methyl and methylene groups for those blockers acting 90% of the way across the voltage drop. This is interpreted as suggesting a hydrophobic binding site at this point in the conduction pathway. The degree of block increases as the concentration of small TAA cations is raised. The concentration dependence of tetraethyl ammonium block indicates that the cation interacts with a single site within the conduction pathway with a Km of 9.8 +/- 1.7 mM (mean +/- SD) at 40 mV. Larger TAA cations (n = 4-5) do not induce voltage-dependent block of potassium current of the form seen with the smaller TAA cations. These data support the contention that the sheep cardiac SR ryanodine receptor channel may be occupied by at most one ion at a time and suggest that a large proportion of the voltage drop falls over a relatively wide region of the conduction pathway.

Animals↗
PubMed1992

Loss of regular oscillatory insulin secretion in islet cell antibody positive non-diabetic subjects.

Basal insulin secretion was compared in nine islet-cell antibody positive, non-diabetic first-degree relatives of children with Type 1 (insulin-dependent) diabetes mellitus and nine normal control subjects matched for age, sex and weight. Acute insulin responses to a 25 g intravenous glucose tolerance test were similar in the two groups (243 (198-229) vs 329 (285-380) mU.l-1 x 10 min-1, mean (+/- SE), p = 0.25). Fasting plasma insulin was assayed in venous samples taken at one min intervals for 2 h. Time series analysis was used to demonstrate oscillatory patterns in plasma insulin. Autocorrelation showed that regular oscillatory activity was generally absent in the islet-cell antibody-positive group, whereas a regular 13 min cycle was shown in control subjects (p less than 0.0001). Fourier transformation did, however, show a 13 min spectral peak in the islet-cell antibody positive group, consistent with intermittent pulsatility. We conclude that overall oscillatory patterns of basal insulin secretion are altered in islet-cell antibody positive subjects even when the acute insulin response is within the normal range.

Activity Cycles↗
PubMed1992

Characteristics of trabecular bone resorption cavities in patients with chronic renal failure.

Using a computerised technique, resorption cavity characteristics in iliac crest trabecular bone were assessed in 30 patients with chronic renal failure and compared with data obtained from healthy subjects. The mean and maximum cavity depth were significantly greater in the patient group (P less than 0.0001); in addition, cavity area, the percentage of bone being remodelled, the number of cavities per mm trabecular surface and the percentage eroded surface were all significantly greater than in controls (P less than 0.0001). However, the surface length of individual cavities in the patient group did not differ significantly from that of controls. In the patient group, serum intact parathyroid hormone concentrations showed a significant positive correlation with mean resorption cavity depth (r = 0.451, P less than 0.05). Our results demonstrate that the increase in bone resorption associated with hyperparathyroidism secondary to chronic renal failure is due to an increase both in the number and depth of cavities, although the surface extent of individual cavities is normal. These findings indicate that factors determining the length of trabecular surface eroded and the depth of individual resorption cavities are controlled by different mechanisms.

Adult↗
PubMed1992

Human HOX4E: a gene strongly expressed in the adult male and female urogenital tracts.

Homeobox-containing genes (Hox genes) are believed to play a fundamental role in development and positional identity. Four homologous Hox gene complexes are found in humans and mice. Genes at the 3' ends of these complexes tend to be expressed rostrally while those at the 5' end are expressed caudally. Whereas complete open reading frames have been reported for rostrally expressed 3' Hox genes, structural information is lacking for the more 5' genes. Genomic and cDNA clones containing the human HOX4E (also known as human Hox 4.5) gene were isolated. The gene contains two exons and spans about 5 kb of DNA. The N-terminal portion of the HOX4E activation domain contains several consensus sequence elements also found in other mammalian AbdB family genes. Further downstream, however, HOX4E contains a novel 37-amino-acid stretch containing 30% acidic residues. Northern blot analysis of HOX4E expression in adult tissues showed a major human transcript of 1.8 kb, the expression of which was largely limited to tissues of the male and female urogenital tracts. Expression was particularly strong in the uterus. This suggests that aside from its effects during embryogenesis, the HOX4E gene may play a continuing role in adult genitourinary tract function.

Adult↗
PubMed1992

Soluble interleukin-2 receptor and disease activity in Crohn's disease.

An ELISA was used to measure concentrations of soluble interleukin-2 receptor (sIL-2R) alpha chain in the sera of patients with Crohn's disease. In a group of 56 patients, serum concentrations of sIL-2R were significantly raised in patients with active disease compared with patients with inactive disease and age-matched control populations. There was a significant correlation between serum sIL-2R concentration and disease activity as assessed by the Harvey-Bradshaw index (r = +0.60; P less than 0.001) and laboratory measurements of disease activity including C-reactive protein (r = +0.79; P less than 0.001), ESR (r = +0.64; P less than 0.001) and platelet count (r = +0.533; P less than 0.001). We also found a negative correlation between sIL-2R levels and serum albumin (r = -0.66; P less than 0.001). In longitudinal studies, changes in the concentration of serum sIL-2R reflected the changes in disease activity. Soluble IL-2R, therefore, offers a new measure of disease activity in Crohn's disease with a potential advantage over other laboratory parameters currently available in that it may reflect more accurately the underlying immunopathogenic process.

Adrenal Cortex Hormones↗
PubMed1992

Large tetraalkyl ammonium cations produce a reduced conductance state in the sheep cardiac sarcoplasmic reticulum Ca(2+)-release channel.

The purified Ca(2+)-release/ryanodine receptor channel of the sheep cardiac muscle sarcoplasmic reticulum (SR) functions as a calcium-activated cation-selective channel under voltage clamp conditions following reconstitution into planar phospholipid bilayers. We have investigated the effect of large tetraalkyl ammonium (TAA) cations, (CnH2n+1)4N+ (n = 4 and 5) on monovalent cation conduction. These cations modify the conductance of the receptor channel at positive holding potentials from the cytosolic side of the channel. Under these conditions, openings are resolved as a mixture of normal full amplitude events and events of reduced conductance. The amplitude of the reduced conductance state is a fixed proportion of the normal open state. As a proportion of all open events, the occurrence of the tetrabutyl ammonium (TBA+) related subconductance state increases with concentration and increasingly positive holding potential. The TBA+ related subconductance state displays similar conduction properties to the unmodified channel; with a linear current-voltage relationship, a similar affinity for K+ and voltage-dependent block by TEA+. A method was used to quantify the voltage dependence of the occurrence of the TBA+ effect, which yielded an effective gating charge of 1.66. A second method based on kinetic analysis of the voltage dependence of transitions between the full open state and the TBA+ related subconductance state produced a similar value. In addition, this analysis revealed that the bulk of the voltage-dependence resided in the off rate. TBA+ related subconductance events, expressed as a proportion of all open events, saturated with increasing TBA+ concentration. Kinetic analysis revealed that this could be entirely accounted for by changes in the on rate. Tetrapentyl ammonium (TPeA+) causes a qualitatively similar effect with a subconductance state of lower amplitude. The voltage-dependence of the effect was comparable to that displayed by TBA+. These findings are interpreted as a form of partial block in which more than one large TAA cation binds at the extremity of the voltage drop to produce an electrostatic barrier for ion translocation.

Animals↗
PubMed1992

Immunotherapy with ciamexon in the non obese diabetic (NOD) mouse.

Ciamexon (CMX), a new immunomodulatory compound acting mainly on B-lymphocytes was given orally to 42 NOD mice divided into three sex and litter matched groups (A: 0.3 mg/mouse/day CMX, B: 1.5 mg/mouse/day CMX, C: control) from 7 weeks of age. Animals were followed up for evaluation of diabetes incidence up to 32 weeks of age. There was a tendency for a delayed onset of hyperglycemia in mice of group B up to 26 weeks of age; however no significant difference in the cumulative incidence of diabetes at 32 weeks of age was observed (A: 57.5%, B: 38.5%, C: 38.5%). No differences were found in the number of infiltrated islets in animals culled at 10 weeks of age treated with CMX from 4 weeks of age. We conclude that CMX does not modify the course of insulitis and diabetes incidence in NOD mice although though the appearance of glycosuria was delayed by this treatment.

Adjuvants, Immunologic↗
PubMed1992

Divalent cation conduction in the ryanodine receptor channel of sheep cardiac muscle sarcoplasmic reticulum.

The conduction properties of the alkaline earth divalent cations were determined in the purified sheep cardiac sarcoplasmic reticulum ryanodine receptor channel after reconstitution into planar phospholipid bilayers. Under bi-ionic conditions there was little difference in permeability among Ba2+, Ca2+, Sr2+, and Mg2+. However, there was a significant difference between the divalent cations and K+, with the divalent cations between 5.8- and 6.7-fold more permeant. Single-channel conductances were determined under symmetrical ionic conditions with 210 mM Ba2+ and Sr2+ and from the single-channel current-voltage relationship under bi-ionic conditions with 210 mM divalent cations and 210 mM K+. Single-channel conductance ranged from 202 pS for Ba2+ to 89 pS for Mg2+ and fell in the sequence Ba2+ greater than Sr2+ greater than Ca2+ greater than Mg2+. Near-maximal single-channel conductance is observed at concentrations as low as 2 mM Ba2+. Single-channel conductance and current measurements in mixtures of Ba(2+)-Mg2+ and Ba(2+)-Ca2+ reveal no anomalous behavior as the mole fraction of the ions is varied. The Ca(2+)-K+ reversal potential determined under bi-ionic conditions was independent of the absolute value of the ion concentrations. The data are compatible with the ryanodine receptor channel acting as a high conductance channel displaying moderate discrimination between divalent and monovalent cations. The channel behaves as though ion translocation occurs in single file with at most one ion able to occupy the conduction pathway at a time.

Animals↗