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Biomedical subjects

E Baker

Publications and source records attributed to E Baker.

At least 145 records · Page 8Linked to original sources
PubMed1994

Two saturable mechanisms of iron uptake from transferrin in human melanoma cells: the effect of transferrin concentration, chelators, and metabolic probes on transferrin and iron uptake.

The mechanisms of iron (Fe) and transferrin (Tf) uptake by the human melanoma cell line, SK-MEL-28, have been investigated using chelators and metabolic probes. These data provide evidence for two saturable processes of Fe uptake from Tf, namely, specific receptor-mediated endocytosis and a second nonspecific, non-receptor-mediated mechanisms which saturated with respect to Fe uptake at a Tf concentration of approximately 0.3 mg/ml. In contrast to Fe uptake, Tf uptake increased linearly up to at least 1 mg/ml. Furthermore, under the culture conditions used, the second nonspecific, non-receptor-mediated mechanism was the most important process in terms of quantitative Fe uptake. Two concentrations of Tf-125I-59Fe (0.01 and 0.1 mg/ml) were used in order to characterise the specific and nonspecific Fe uptake pathways. Membrane permeable chelators were equally effective at both Tf concentrations, whereas membrane impermeable chelators were significantly (P < 0.001) more effective at reducing the internalisation of Fe at the higher Tf concentration, consistent with a mechanism of Fe uptake which occurred at a site in contact with the extracellular medium. The oxidoreductase inhibitor, amiloride, only slightly inhibited Fe uptake at the higher Tf concentration, suggesting that the second nonspecific process was not mediated by a diferric Tf reductase. Three lysosomotrophic agents and the endocytosis inhibitor, phenylglyoxal, markedly reduced Fe uptake at both Tf concentrations, and it is concluded that a saturable process consistent with receptor-mediated endocytosis of Tf occurred at the lower Tf concentration, while the predominant mechanism of Fe uptake at high Tf concentrations was a second saturable process consistent with adsorptive pinocytosis.

Humans↗
PubMed1994

Neurotoxicity of glucocorticoids in the primate brain.

Severe and prolonged physical and psychological stress is known to cause brain damage; long-term torture victims in prison have later developed psychiatric disorders and cerebral cortical atrophy observed in CT scans (Jensen, Genefke, Hyldebrandt, Pedersen, Petersen, and Weile, 1982). In nonhuman primates, we observed degeneration and depletion of the hippocampal neurons in African green monkeys that had been severely abused by cagemates and died with complications of multiple gastric ulcers and adrenal cortical hyperplasia (Uno, Tarara, Else, Suleman and Sapolsky, 1989). In our previous studies the administration of dexamethasone (DEX) (5 mg/kg) to pregnant rhesus monkeys at 132 to 133 days of gestation induced degeneration and depletion of the hippocampal pyramidal and dentate granular neurons in the brains of 135-gestation-day fetuses, and these changes were retained in the brains of fetuses at near term, 165 days of gestation (Uno, Lohmiller, Thieme, Kemnitz, Engle, Roecker, and Farrell, 1990). We also found that implantation of a cortisol pellet in the vicinity of the hippocampus in adult vervet monkeys induced degeneration of the CA3 pyramidal neurons and their dendritic branches (Sapolsky, Uno, Rebert, and Finch, 1990). Thus, hippocampal pyramidal neurons containing a high concentration of glucocorticoid receptors appear to be highly vulnerable to either hypercortisolemia caused by severe stress or to exposure to exogenous glucocorticoids. To study the long-term postnatal sequelae of prenatal brain damage, eight rhesus monkeys were treated with either DEX (5 mg/kg), 5 animals, or vehicle, 3 animals, at 132 to 133 days of gestation. After natural birth, all animals lived with their mothers for 1 year. At 9 months of age, we found that DEX-treated animals had significantly high plasma cortisol at both base and post-stress (isolation) levels compared to age-matched vehicle-treated animals. Magnetic resonance images (MRI) of the brain at 20 months of age showed an approximately 30% reduction in size and segmental volumes of the hippocampus in DEX-treated compared to vehicle-treated animals. Measurements of whole brain volume by MRI showed no significant differences between DEX and vehicle groups. Prenatal administration of a potent glucocorticoid (DEX) induced an irreversible deficiency of the hippocampal neurons and high plasma cortisol at the circadian baseline and post-stress levels in juvenile rhesus monkeys. These results suggest that the hippocampus mediates negative feedback of cortisol release; a lack or deficiency of the hippocampal neurons attenuates this feedback resulting in hypercortisolemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Genomic organization, exact localization, and tissue expression of the human CD26 (dipeptidyl peptidase IV) gene.

CD26 is a lymphocyte cell surface antigen which is increased during T-cell activation and is also expressed in other tissues. It is an atypical serine protease belonging to the prolyl oligopeptidase family. CD26 has been implicated in a variety of biological functions including T-cell activation, cell-to-cell adhesion, and recently in HIV infection. This paper describes, through the isolation and partial sequencing of eight human CD26 genomic clones, the first information on the genomic organization of the prolyl oligopeptidase family. We have established that the human CD26 gene spans approximately 70 kilobases (kb) and contains 26 exons, ranging in size from 45 base pairs (bp) to 1.4 kb. The nucleotides that encode the serine recognition site (G-W-S-Y-G) are split between two exons. This clearly distinguishes the genomic organization of the prolyl oligopeptidase family from that of the classical serine protease family. The 5' flanking domain of the CD26 gene contains neither a TATA box nor a CAAT box, but a 300 bp region extremely rich in C and G (72%) contains potential binding sites for several transcriptional factors. The human CD26 gene encodes two messages sized at about 4.2 and 2.8 kb. These are both expressed at high levels in the placenta and kidney and at moderate levels in the lung and liver. Only the 4.2 kb mRNA was expressed at low levels in skeletal muscle, heart, brain, and pancreas. Fluorescence in situ hybridization on metaphase chromosome spreads located the human CD26 gene to the long arm of chromosome 2(2q24.3).

Amino Acid Sequence↗
PubMed1994

Characterization of CGRP receptors in various regions of gerbil brain.

The distribution of specific calcitonin gene-related peptide (CGRP) binding sites was investigated in gerbil brain regions such as cortex, cerebellum, hypothalamus, and hippocampus. The binding of [125I]CGRP to membranes prepared from these regions of the gerbil brain was rapid, saturable and specific with dissociation constants (Kd) between 10-40 pM and maximum binding (Bmax) between 10-30 fmol/mg protein. Human and rat CGRP and hCGRP8-37 competed for [125I]hCGRP binding in a concentration-dependent manner with a Ki of 10-100 pM. Salmon calcitonin was very weak in competing for [125I]hCGRP binding (ki > 10 microM). CGRP did not stimulate adenylate cyclase in these brain regions. Cross-linking of [125I] hCGRP to the brain membrane fractions with disuccinimidyl suberate revealed specific incorporation of [125I] hCGRP to a protein band of approximate molecular weight 52 kDa.

Adenylyl Cyclases↗
PubMed1994

Physical linkage of the fragile site FRA11B and a Jacobsen syndrome chromosome deletion breakpoint in 11q23.3.

Autosomal fragile sites, unlike their X-linked counterparts, are not known to be associated with disease. However, one case report has highlighted a possible relationship between the inheritance of a rare folate-sensitive fragile site in band 11q23.3 (FRA11B) and the chromosome 11q23-->qter deletion in Jacobsen (11q-) syndrome. The mother and brother of the reported Jacobsen syndrome child are FRA11B carriers, suggesting that in vivo breakage at the fragile site during early development could have given rise to the chromosome deletion. We have tested this hypothesis by high resolution physical mapping of FRA11B and of the deletion chromosome breakpoint in the Jacobsen syndrome patient. A detailed restriction map of 600 kb of human chromosome band 11q23.3 has been assembled which covers the PBGD, CBL2 and THY1 genes. FISH experiments with YACs and cosmids from this region have localised FRA11B to an interval of approximately 100 kb containing the 5' end of the CBL2 gene, which includes a CCG trinucleotide repeat. This class of repeat is expanded in the four cloned examples of fragile site and therefore the CBL2 repeat is a candidate for the location of FRA11B. Further, it is shown that the chromosomal deletion breakpoint of the Jacobsen syndrome child maps within the same interval as the fragile site. The breakpoint has apparently been repaired and stabilised by the de novo addition of a telomere. These data are consistent with a role for an inherited fragile site in the aetiology of a chromosome deletion syndrome.

Abnormalities, Multiple↗
PubMed1994

Longitudinal monitoring of intracranial arterial stenoses with transcranial Doppler ultrasonography.

The natural history of intracranial arterial stenoses remains relatively unknown. To monitor the progression of these lesions over time, the authors reviewed transcranial Doppler (TCD) laboratory reports at five hospitals for patients with angiographically documented intracranial arterial stenoses along the internal carotid artery distribution, and at least two TCD studies conducted more than 2 months apart. Twenty-two patients (19 men and 3 women; mean age, 64 years) with 29 stenoses were identified. The findings were compared to reproducibility data obtained from 11 age-matched control subjects with repeat TCD studies. During a mean follow-up period of 21 months, peak systolic flow velocities corresponding to the areas of stenosis increased in 9 arteries with lesions, and new collateral flow patterns, indicating further hemodynamic compromise distal to the lesions, developed in 2; one of the latter also had increased corresponding velocities. Thus, 10 (35%) arteries with lesions had TCD evidence of progression. Flow velocities remained the same in 13 (45%) stenotic vessels and dropped in 2 (7%). Findings were considered inconclusive for 4 lesions (14%). These findings suggest that intracranial arterial stenoses are dynamic lesions, and that they can evolve and cause further reductions of the arterial diameters after relatively short periods of time. TCD can noninvasively detect their hemodynamic effects.

Adult↗
PubMed1994

Characterization of a functional angiotensin II receptor in Xenopus laevis heart.

High-affinity (104 +/- 18 pmol/l) and high-density (204 +/- 25 fmol/mg) angiotensin II (AII) binding sites have been identified in Xenopus laevis heart membranes. Competition binding of [125I]Sar1,Ile8 angiotensin (SIA) to these receptors by peptide analogs selective for the mammalian AII receptor subtypes AT1 and AT2 suggested that the amphibian AII binding sites were more closely related to the AT1 receptor subtype. Also in common with AT1 receptors, dithiothreitol and GTP gamma S inhibited [125I]SIA binding to Xenopus heart receptors, exhibiting IC50 values of 600 and 0.95 mumol/l, respectively. In addition, Xenopus oocytes injected with Xenopus heart mRNA were capable of mobilizing calcium when exposed to AII, demonstrating that Xenopus AII receptors are functionally linked to a second-messenger system similar to that coupled to mammalian AT1 receptors. However, in contrast to both AT1 and AT2 receptor subtypes, nonpeptide antagonists DUP 753 and SK&F 108566 (AT1 receptor selective) and PD123319 (AT2 selective) did not bind the Xenopus AII receptors, thus establishing that the amphibian receptors were pharmacologically unique. Together, these results demonstrate that Xenopus heart AII receptors are functionally similar to mammalian AT1 receptors but are pharmacologically distinct from both AT1 and AT2 receptors.

1-Sarcosine-8-Isoleucine Angiotensin II↗
PubMed1994

Vitamin activities in human portal, hepatic and femoral blood after vitamin ingestion.

The dynamics of intestinal absorption, blood concentration and distribution of thiamin, biotin, nicotinate, riboflavin, pantothenate, various folates (folic acid, folinic acid, pteroyltriglutamate), vitamins A, E, C, B12, and B6 were monitored in 12 patients by multiple simultaneous sampling of blood obtained by combined catheterization of portal vein, hepatic vein, and femoral artery after vitamin ingestion. All water-soluble vitamins proved elevated after vitamin ingestion principally in portal blood within 10 minutes as compared with hepatic and femoral blood. Elevated vitamin levels in portal blood--compared to hepatic and femoral blood--remained high even after 120 min. indicating that absorption from the gut was still progressing. In contrast, ingestion of the fat-soluble vitamins A and E evoked no elevated vitamin activity in portal blood. Within 10 min. after vitamin ingestion, all folates were converted into reduced and methylated 5-methyltetrahydrofolate (5-CH3THF) on passage through the gut. At this time, portal blood elevation of 5-CH3THF persisted before its elevation in hepatic or femoral blood. Presumably, the elevation was not due to the flushing of stored 5-CH5THF from tissues but rather of folate conversion to 5-CH3THF upon gut passage. The significance of these findings is discussed.

Administration, Oral↗
PubMed1993

CD30 antigen, a marker for Hodgkin's lymphoma, is a receptor whose ligand defines an emerging family of cytokines with homology to TNF.

CD30 is a surface marker for neoplastic cells of Hodgkin's lymphoma and shows sequence homology to members of the tumor necrosis factor (TNF) receptor superfamily. Using a chimeric probe consisting of the extracellular domain of CD30 fused to truncated immunoglobulin heavy chains, we expression cloned the cDNA cognate from the murine T cell clone 7B9. The encoded protein is a 239 amino acid type II membrane protein whose C-terminal domain shows significant homology to TNF alpha, TNF beta, and the CD40L. Cross-hybridization to an induced peripheral blood T cell cDNA library yielded the human homolog, which is 72% identical at the amino acid level. The recombinant human ligand enhances the proliferation of CD3-activated T cells yet induces differential responses, including cell death, in several CD30+ lymphoma-derived clones. The human and murine genes map to 9q33 and the proximal region of chromosome 4, respectively.

Amino Acid Sequence↗
PubMed1993

A cytokine receptor gene cluster in the X-Y pseudoautosomal region?

The receptors for interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) are heterodimers comprised of ligand specific alpha chains and a common beta chain. The genes encoding the IL-5 receptor alpha chain and the common beta chain reside on chromosome 3 and 22 respectively, while the GM-CSF receptor alpha chain gene (CSF2RA) has been mapped to the pseudoautosomal region (PAR) of the sex chromosomes, which is a 2.6-Mb stretch of homologous sequence at the tips of the short arms within which a single obligatory recombination occurs during male meiosis. We have mapped the gene encoding the IL-3 receptor alpha chain (IL3RA) to the sex chromosomes by polymerase chain reaction (PCR) analysis of human-mouse or human-chinese hamster cell hybrids, and to Yp13.3 and Xp22.3 using fluorescence in situ hybridization. To explore the possibility that IL3RA is located within the pseudoautosomal region we screened the Centre d'Etude du Polymorphisme Humain (CEPH) pedigrees for an informative-restriction fragment-length polymorphism (RFLP) that showed male meiotic recombination. Two informative CEPH pedigrees were identified that displayed this phenomenon, confirming the psuedoautosomal location of IL3RA. Using long-range restriction mapping we have found that IL3RA maps to the same 190-kb restriction fragment as CSF2RA, suggesting that a cytokine receptor gene cluster may reside in the PAR.

Base Sequence↗
PubMed1993

Medial paraspinal muscle electromyography: techniques of examination.

We describe two techniques, developed through cadaveric dissections, for the electromyographic examination of the lumbar interspinal muscles and medial lumbar multifidi. Previous anatomic studies have indicated that these medial paraspinal muscles share unisegmental innervation by a single nerve root. Electromyography of these muscles may therefore improve the localization of lumbosacral radiculopathy. The ability of the two techniques to achieve appropriate needle placement was confirmed using percutaneous injection of colored latex into cadavers. The safety and feasibility of the techniques were confirmed in healthy volunteers. Further studies are underway in subjects with lumbosacral radiculopathy to determine the clinical utility of these techniques.

Adult↗
PubMed1993

Unusual behaviour of a human autosome having two rare folate sensitive fragile sites.

A mother and daughter who have two rare folate sensitive fragile sites on the same homolog of chromosome 12 are recorded. This confirms the folate sensitive nature of the fragile site at 12q24.13. The behaviour of the chromosome with the two fragile sites is described, which includes the propensity for the two fragile sites to associate with each other when simultaneously expressed.

Adult↗
PubMed1993

Molecular cloning and chromosomal localisation of the human homologue of a receptor related to tyrosine kinases (RYK).

A cDNA encoding the human homologue of mouse RYK (related to receptor tyrosine kinases) has been cloned from an interleukin 1 (IL-1)-stimulated human hepatoma cDNA library by cross-species hybridization using the mouse RYK cDNA as a probe. The sequence of the 3067-bp cDNA clone encoding human RYK predicts a transmembrane protein with a cytoplasmic domain that contains the consensus sequences (subdomains I-XI) of the protein tyrosine kinase (PTK) family. The highly conserved motif -D-F-G- (subdomain VII) of the catalytic domain of other receptor-type tyrosine kinases is altered to -D-N-A- in human RYK. In addition, a number of other changes were found in the ATP binding site (subdomains I and II) and the motif [-I-H-R-D-L-A-A-R-N-] found in subdomain VI. Comparison of the human and mouse RYK sequences shows a 92% conservation at the nucleotide level and 97% at the amino acid level. There was no significant homology between the extracellular domain of RYK and the other families of receptor tyrosine kinases described to date. RYK therefore appears to define a new subclass of receptor-type tyrosine kinases whose structure has remained highly conserved across species.

Amino Acid Sequence↗