Biomedical subjects

J Chambers

Publications and source records attributed to J Chambers.

At least 19 recordsLinked to original sources

PubMed1992

Alternative exon usage and processing of the major histocompatibility complex-encoded proteasome subunits.

The finding that two subunits of the proteasome, LMP2 and LMP7, are encoded in the major histocompatibility complex (MHC) has linked the proteasome which represents a major extralysosomal proteolytic system to the processing of intracellular antigens. Here we describe a second form of the human LMP7 cDNA, LMP7-E2, which has been identified during the characterization of novel genes in the MHC. The analysis of the genome organization of LMP7 revealed that LMP7-E1 and LMP7-E2 arise by alternative exon usage. Using specific antibodies against LMP2 and LMP7, we show that they are co-expressed with class I MHC molecules as well as a putative peptide transporter. The polypeptides encoded by LMP7 and LMP2 undergo proteolytic processing when incorporated into proteasomes, and the LMP7 precursor is derived mainly from LMP7-E2. Furthermore, our data suggest that LMP7 and LMP2 are mutually dependent for their incorporation into the proteasomal complex.

Amino Acid Sequence↗

PubMed1992

6-substituted decahydroisoquinoline-3-carboxylic acids as potent and selective conformationally constrained NMDA receptor antagonists.

We have prepared a series of 6-substituted decahydroisoquinoline-3-carboxylic acids, and structurally similar analogs, as potential N-methyl-D-aspartate receptor antagonists. There is a large body of evidence to support the use of such compounds as cerebroprotective agents in a variety of acute and chronic neurodegenerative disorders, where some component of glutamate-mediated excitotoxicity may exist. The compounds prepared were evaluated in vitro in both receptor binding assays ([3H]CGS19755, [3H]AMPA, and [3H]kainic acid) and in a cortical wedge preparation (versus NMDA, AMPA, and kainic acid) to determine affinity, potency, and selectivity. The new amino acids were also evaluated in vivo for their ability to block NMDA-induced lethality in mice. We synthesized many of the possible diastereomers of the decahydroisoquinoline nucleus in order to examine the spatial and steric requirements for affinity at the NMDA receptor and activity as NMDA antagonists. From our structure-activity relationship we identified two potent and selective NMDA receptor antagonists, the phosphonate- and tetrazole-substituted amino acids 31a and 32a, respectively, that show good activity in animals following systemic administration. For example, 31a and 32a selectively displaced [3H]CGS19755 binding with IC50S of 55 +/- 14 and 856 +/- 136 nM, respectively, and selectively antagonized responses due to NMDA in a cortical wedge preparation with IC50S of 0.15 +/- 0.01 and 1.39 +/- 0.29 microM, respectively. And compounds 31a and 32a blocked NMDA-induced lethality in mice with minimum effective doses of 1.25 and 2.5 mg/kg (intraperitoneal), respectively. These novel amino acids are among some of the most potent NMDA antagonists described thus far, and are excellent candidates for development as neuroprotective agents for a number of CNS disorders.

Animals↗

PubMed1992

Major histocompatibility complex (MHC)-encoded HAM2 is necessary for antigenic peptide loading onto class I MHC molecules.

The mutant murine lymphoma cell line RMA-S is unable to present endogenous antigens due to its inability to efficiently assemble class I major histocompatibility complex molecules and antigenic peptides. Therefore, it has been suggested that RMA-S cells are defective either in peptide generation or in peptide transport into the endoplasmic reticulum, where class I major histocompatibility complex molecule assembly is believed to occur. As proteasomes and the putative peptide transporters HAM1 and HAM2 have been implicated in class I antigen processing, we have investigated their expression in RMA-S and its wild-type counterpart RMA. Both proteasomes and HAM1 proteins are expressed at similar levels and show identical subcellular distributions in the two cell lines. However, only one copy of the HAM2 gene is present in RMA-S cells, and it contains a point mutation that leads to a premature stop codon. Thus, the HAM2 protein is absent from RMA-S cells. These data demonstrate that HAM2 is essential for peptide loading onto class I molecules.

Amino Acid Sequence↗

PubMed1992

The Hatle orifice area formula tested in normal bileaflet mechanical mitral prostheses.

The Hatle formula was derived empirically in native mitral stenosis and may not be valid for normal prosthetic valves. Bileaflet mechanical prostheses open fully at low flows and have minimal interindividual variation in orifice area. In these valves effective area and measured manufacturer's area should be similar. We studied 60 patients aged 58 +/- 12 yr at a mean of 5 months after implantation with a CarboMedics prosthesis. There was a coexistent aortic prosthesis in 21. All diastolic measurements were averaged over 5 beats and stroke volume was calculated from the integral of the subaortic velocity trace and the cross-sectional area of the left ventricular outflow tract. For the whole group, area by the Hatle formula was 3.1 +/- 0.7 cm2 and measured area was 2.8 +/- 0.4 cm2. There was no significant correlation between these values (p = 0.329). Pressure half-time was more closely correlated with peak transmitral velocity (p = 0.012), RR interval (p = 0.015), diastolic time interval (p = 0.062) and stroke volume (p = 0.074). We conclude that the Hatle formula should not be applied to normal bileaflet mitral prostheses where pressure half-time reflects nonprosthetic factors more closely than orifice area.

Aged↗

PubMed1992

Characterization of mutations in phenotypic variants of hypoxanthine phosphoribosyltransferase deficiency.

The Lesch-Nyhan disease is caused by an almost complete lack of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). Partial HPRT-deficiency, associated with less severe phenotype, has also been identified. We have characterized mutations occurring in HPRT cDNA isolated from patients with HPRT-deficiency with an emphasis on examining the more unusual partial variants of HPRT-deficiency. HPRT cDNA was amplified by PCR, cloned and analyzed by automated DNA sequence analysis. Twenty-two, unrelated individuals with HPRT deficiency were studied including eight classic Lesch-Nyhan patients and fourteen patients representing the different groups of partial HPRT deficiency. We found a diverse pattern of mutations with point mutations accounting for the majority of abnormal HPRT genes. Nonsense mutations and exon deletions were only found in HPRT cDNA isolated from classic Lesch-Nyhan patients. Mutations associated with partial HPRT-deficiency were frequently located in the amino terminal part of the molecule. A CpG mutational hot spot was identified at the position for Arg-51 in the HPRT protein. Two hyperuricemic patients exhibited unusual splice site mutations: in one this led to the creation of an additional exon in the HPRT gene and in the other part of exon 6 was missing in a subpopulation of the transcripts, producing the effect of a dominant, negative mutation.

Amino Acid Sequence↗

PubMed1992

Sodium-lithium countertransport activity and insulin resistance in normotensive IDDM patients.

In insulin-dependent diabetes (IDDM), an overactivity of sodium-lithium countertransport (Na+/Li+ CT) has been associated with the risk of nephropathy and hypertension, two conditions of insulin resistance. We investigated the sensitivity to insulin with a hyperinsulinemic (approximately 719 pM [approximately 100 microU/ml]) euglycemic clamp in two groups of normotensive nonproteinuric IDDM patients; 12 (10 men, 2 women) had high Na+/Li+ CT activity (mean 0.47, range 0.42-0.68 mmol/L red blood cells [RBC]/h, group 1) and 12 (9 men, 3 women) had normal Na+/Li+ CT activity (mean 0.24, range 0.12-0.31 mmol/L RBC/h, group 2). The two groups were similar in age (mean +/- SE 36 +/- 2 vs. 33 +/- 1 yr), duration of diabetes (19 +/- 3 vs. 18 +/- 2 yr), body mass index (26 +/- 0.8 vs. 24 +/- 0.6 kg/m2), arterial blood pressure (systolic/diastolic 121 +/- 4/79 +/- 2 vs. 122 +/- 3/77 +/- 2 mmHg), and glycemic control (HbA1 8.5 +/- 0.4 vs. 8.0 +/- 0.4%). Albumin excretion rate (AER) ranged between 4.7 and 148 (geometric mean 14) micrograms/min in group 1 and between 2.7 and 93 (geometric mean 11) micrograms/min in group 2. There were four microalbuminuric patients (AER greater than 30 micrograms/min) in each group. Whole-body glucose uptake was significantly reduced on average in group 1 compared with group 2 (41.6 +/- 2.2 mumol.kg-1.min-1 [7.48 +/- 0.4 mg.kg-1.min-1] vs. 49.6 +/- 2.2 mumol.kg-1.min-1 [8.93 +/- 0.4 mg.kg-1.min-1, P = 0.03), but some overlap existed between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Limitations and pitfalls in the assessment of prosthetic valves with Doppler ultrasonography.

Normal Doppler-derived data for new prosthetic designs are currently gathered after marketing. Therefore the cardiologist needing to assess a new valve may need to equate Doppler results with data gathered invasively during premarket testing. This invites error because catheterization and Doppler ultrasonography are not always directly comparable. This review discusses difficulties in defining normal prosthetic function and problems arising from the comparison of catheter and Doppler data. It concludes that (1) the hemodynamic formulas in current use have limitations when applied to normally functioning prosthetic valves, (2) patterns of normal regurgitation differ widely between different valve designs and may occasionally resemble paraprosthetic leaks, (3) there is a good case for reporting only raw Doppler data rather than derived pressure drop or effective orifice area, (4) a new prosthetic design should be tested in vivo with Doppler ultrasonography before marketing, and (5) nonprosthetic factors affecting Doppler data and flow information should always be given.

Cardiac Catheterization↗

PubMed1991

Smoking.

Explore the source record for details and available documents.

Advertising↗

PubMed1991

A randomized double-blind crossover comparison of four rate-responsive pacing modes.

The aim of this study was to compare, both subjectively and objectively, four modern rate-responsive pacing modes in a double-blind crossover design. Twenty-two patients, aged 18 to 81 years, had an activity-sensing dual chamber universal rate-responsive (DDDR) pacemaker implanted for treatment of high grade atrioventricular block and chronotropic incompetence. They were randomly programmed to VVIR (ventricular demand rate-responsive), DDIR (dual chamber demand rate-responsive), DDD (dual chamber universal) or DDDR (dual chamber universal rate-responsive) mode and assessed after 4 weeks of out-of-hospital activity. Five patients, all with VVIR pacing, requested early reprogramming. The DDDR mode was preferred by 59% of patients; the VVIR mode was the least acceptable mode in 73%. Perceived "general well-being," exercise capacity, functional status and symptoms were significantly worse in the VVIR than in dual rate-responsive modes. Exercise treadmill time was longer in DDDR mode (p less than 0.01), but similar in all other modes. During standardized daily activities, heart rate in VVIR and DDIR modes underresponded to mental stress. All rate-augmented modes overresponded to staircase descent, whereas the DDD mode significantly underresponded to staircase ascent. Echocardiography revealed no difference in chamber dimensions, left ventricular fractional shortening or pulmonary artery pressure in any mode. Cardiac output was greater at rest in the dual modes than in the VVIR mode (p = 0.006) but was similar at 120 beats/min. Beat to beat variability of cardiac output was greatest in VVIR mode (p less than 0.0001), with DDIR showing greater variability than DDD or DDDR modes (p less than 0.05). Mitral regurgitation estimated by Doppler color flow imaging was similar in all modes, but tricuspid regurgitation was significantly greater in VVIR than in dual modes (p less than 0.03). Subjects who preferred the DDDR mode and those who found the VVIR mode least acceptable had significantly greater increases in stroke volume when paced in the DDD mode than in the ventricular-inhibited (VVI) mode at rest (22%) when compared with subjects who preferred other modes (2%, p = 0.03). No other objective variable was predictive of subjective benefit from any rate-responsive pacing mode. Thus, dual sensor rate-responsive pacing (DDDR) is superior objectively and subjectively to single sensor (VVIR, DDIR and DDD) pacing and subjective benefit from dual chamber rate-augmented pacing is predictable echocardiographically.

Adult↗

PubMed1991

Surgical treatment of sacral fracture in a horse.

An 8-year-old Arabian stallion had signs of severe tailhead pruritus and slowly progressive loss of tail tone for 3 months. Palpation per rectum and radiography of the sacrocaudal region revealed a transverse, ventrally displaced fracture of the caudal portion of the sacrum. Surgical decompression and tail amputation resulted in complete recovery of athletic and reproductive function. Evidence of cauda equina neuritis was not seen on histologic examination of nerve roots obtained at surgery.

Amputation, Surgical↗

PubMed1991

The continuity equation tested in a bileaflet aortic prosthesis.

The continuity equation is valid for a population of aortic valves, but its accuracy in individual valves is uncertain. In bileaflet prostheses, obstruction to forward flow is small and individual variability in opening behaviour is minimal. In these valves, the area of the effective orifice should be close to that measured by the manufacturer. A total of 57 patients aged 58 +/- 11 years were studied at a mean of 3.6 months after implantation with a CarboMedics aortic prosthesis. Nine had additional implants in the mitral position and all prostheses were clinically normal. Peak subaortic and transaortic velocities were averaged over 5 beats. The area of the effective orifice was significantly different between the four diameters (P less than 0.00001), and the correlation between the effective and measured area of the orifice was moderate (rs = 0.73, P less than 0.00003). The 95% range for the differences between individual pairs of values, however, was 0.16 +/- 0.61 cm2. Discrepancies probably arose in the estimation of subaortic cross-sectional area and subaortic velocity. Thus, the continuity equation may be inaccurate in an individual prosthetic valve when functioning normally.

Aged↗

PubMed1991

Millipore analysis of valvular fluid in sterile valve malfunctions.

Malfunctions of sterile shunts may result from valvular dysfunction. The cerebrospinal fluid shunt valves of 14 patients were excised during surgery for sterile shunt malfunctions. In 6 patients, the malfunction was due specifically to a valve malfunction. Cerebrospinal fluid from each valve was passed through a millipore filter, which was then stained using either hematoxylin and eosin or periodic acid-Schiff. The stained millipore filters were examined by a neuropathologist who was unaware of the cause of the shunt malfunction. Although inflammatory cells were detected in all cases, the patients with valve malfunctions were found to have numerous macrophages and giant multinucleated reactive cells within their valves, while cerebrospinal fluid from valves that had been removed during shunt revisions for reasons other than a malfunctioning valve contained only rare mononuclear cells or macrophages. No valve contained erythrocytes, fibrinous matter, neural or glial tissue, or choroid plexus. The possible causes of valve malfunction, including infection and allergic reactions, are discussed. All patients did well after simple replacement of the valve.

Adolescent↗

PubMed1991

Cardiovascular responses to graded reductions in leg perfusion in exercising humans.

Our objective was to determine whether the chemoreflex from human muscle is elicited by small graded reductions in muscle blood flow (MBF) during mild exercise or whether this reflex has an obvious threshold associated with large changes in femoral venous lactate and H+ levels (i.e., as in dogs with high muscle oxidative capacity). Seven subjects exercised supine at 40, 87, and 142 W; lower body positive pressure (LBPP) was applied in 3-min steps at 25, 35, 45, and 50-60 mmHg with the lower body and the cycle ergometer in a sealed box. Estimated MBF (Fick) fell by 5.3 +/- 4.3 to 19.9 +/- 3.8% at four levels of LBPP over three work rates. Mean arterial pressure (MAP), heart rate (HR), and plasma norepinephrine (NE) concentration rose with increasing LBPP. MAP was significantly correlated with femoral venous pH, lactate, O2 tension, and O2 content during moderate and heavy exercise, without an apparent threshold. Percentage decreases in muscle vascular conductance exceeded the decreases in MBF twofold, indicating significant opposition to reduction in MBF by the chemoreflex. Approximately 50% of the correction of MBF back toward control (i.e., at 0 LBPP) could be explained by increased cardiac output, calculated from the rise in HR; the remaining correction could be attributed to both sympathetic vasoconstriction (indicated by high NE levels) and to mechanical effects of partial occlusion. Results suggest that in humans stepwise reductions in MBF gradually elicit muscle chemoreflexes with no apparent threshold at these levels of exercise.

Adult↗

PubMed1991

Health education in England: a five-year strategy for the Health Education Authority.

The Health Education Authority in England has published its first Strategic Plan, covering the years 1990-1995. The origins and functions of the Authority are described, as are the various factors contributing to the Plan. The strategic objective is defined as being "to ensure that by the year 2,000 the people of England are more knowledgeable, better motivated, and more able to acquire and maintain good health," as suggested by six criteria for program effectiveness. Selected programs include HIV/AIDS, coronary heart disease, cancer, smoking, alcohol, nutrition, and family and child health. Complementary delivery methods are examined, such as use of the mass media, the National Health Service, schools and colleges, and the workplace, utilizing partnerships with health, education, and other agencies, promoting professional development, and dissemination of research and local initiative results.

Aged↗

PubMed1991

Diagnosis under random conditions of all disorders of the renin-angiotensin-aldosterone axis, including primary hyperaldosteronism.

Theoretically, the relationship between plasma aldosterone (PA) and PRA in normal subjects under random conditions should differ from that in patients with primary hyperaldosteronism or primary adrenal failure, but should be similar to that in patients with secondary hyperaldosteronism or hyporeninemic hypoaldosteronism. PA, expressed as a function of PRA, the PA/PRA ratio, provides an index of adrenal sensitivity in normal subjects under routine conditions. The random PA/PRA ratios in patients with primary adrenal disorders did not overlap with those in normal subjects, patients with secondary adrenal disorders, hypertensive subjects, or other patients. A single elevated PA/PRA ratio, i.e. more than 920, associated with elevated PA in 4 patients or normal PA in 6 patients indicated primary hyperaldosteronism in 10 patients. However, 5 of 17 patients with chronic renal failure had elevated PA/PRA ratios, but did not have primary hyperaldosteronism. All 14 patients with secondary hyperaldosteronism had elevated PA associated with normal PA/PRA ratios. A single PA/PRA ratio of less than 28 associated with low PA in 18 patients and a normal PA in 1 patient indicated primary adrenal insufficiency, while a low PA associated with a normal PA/PRA ratio indicated hyporeninemic hypoaldosteronism in 7 patients. Fifty-nine patients with nonadrenal disorders other than renal failure had normal PA and PA/PRA ratios. Therefore, with the exception of patients with advanced renal failure, only a single blood sample is required to establish all diagnoses of disorders of the renin-angiotensin-aldosterone axis under random conditions.

Biomarkers↗

PubMed1991

Separation of two subpopulations of old human fibroblasts by mitochondria (rhodamine 123) fluorescence.

The mitochondria-binding fluorescent dye rhodamine 123 (R123) was used to sort two subpopulations of cells from mass cultures of old human fibroblasts (HF). Both subpopulations showed unusual dye retention kinetics when compared to young HF. Additionally, electron microscopy revealed differences in numerical density of mitochondria between young and old HF. Moreover, the two subpopulations exhibited differences in radiolabeled thymidine incorporation and proliferative capacity. The results obtained suggest a possible relationship between mitochondria, proliferative potential and cellular aging.

Cell Division↗

PubMed1990

Virus-induced autoantibody response to a transgenic viral antigen.

The induction of autoantibodies and their possible role in the pathogenesis of autoimmune disease are poorly understood. Involvement of infectious agents has been suspected, but direct evidence is sparse. Whether immunological unresponsiveness to self by antibody-forming B cells is maintained by clonal abortion, clonal anergy or suppression, or how the scenario of interactions between helper T cells, B cells and antigen-presenting cells is distorted in autoantibody responses, is being analysed and widely debated. To evaluate tolerance of neutralizing B-cell responses we used transgenic mice expressing the cell membrane associated glycoprotein (G) of vesicular stomatitis virus (VSV) as self-antigen. We show that autoantibodies to VSV-G cannot be induced by VSV-G in adjuvant or by recombinant vaccinia virus expressing VSV-G, but are triggered by infection with wild-type VSV. The data show that helper T-cell tolerance is crucial in maintenance of B-cell non-reactivity and that cognate T-B recognition is necessary to break tolerance of self-reactive B cells. These results may help to understand mechanisms of virus-induced autoimmunity.

Animals↗

PubMed1990

Splice junction mutations in a yeast tRNA gene which alter the rate and precision of processing.

We have introduced mutations into a tRNALeu3 gene which alter the intron boundaries and examined their effects on RNA splicing. Our results show that the 5'-proximal splice junction is not specified by the position of an adjacent base-paired stem present in all naturally occurring tRNA precursors. Also, efficient cleavage of 5'-splice junctions unique to these mutants, -CpU-, -UpA- and -UpG-, indicates the purine found at the 5'-side of this site in all natural precursors is dispensable. Some alterations of the sequence and structure at the 5'-proximal splice site reduce the rate of cleavage therein and result in accumulation of molecules composed of the 5'-half of the tRNA plus the intron. The precise position of the 5'-proximal cleavage site can vary +/- 1 base in these mutants. The 3'-proximal splice junction is rendered inactive by changing the prospective splice junction sequence from -ApC- to -CpC- and reducing the size of an unpaired loop at this site from six to two bases. Very small amounts of RNA composed of the 3'-half of the tRNA plus the intron accumulate from this precursor. We conclude that splice junction sequence and structure affect both the rate and precision of intervening sequence removal.

Base Sequence↗