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Biomedical subjects

J Linton

Publications and source records attributed to J Linton.

18 recordsLinked to original sources
PubMed2001

Identification and characterization of a novel extracellular matrix protein nephronectin that is associated with integrin alpha8beta1 in the embryonic kidney.

The epithelial-mesenchymal interactions required for kidney organogenesis are disrupted in mice lacking the integrin alpha8beta1. None of this integrin's known ligands, however, appears to account for this phenotype. To identify a more relevant ligand, a soluble integrin alpha8beta1 heterodimer fused to alkaline phosphatase (AP) has been used to probe blots and cDNA libraries. In newborn mouse kidney extracts, alpha8beta1-AP detects a novel ligand of 70-90 kD. This protein, named nephronectin, is an extracellular matrix protein with five EGF-like repeats, a mucin region containing a RGD sequence, and a COOH-terminal MAM domain. Integrin alpha8beta1 and several additional RGD-binding integrins bind nephronectin. Nephronectin mRNA is expressed in the ureteric bud epithelium, whereas alpha8beta1 is expressed in the metanephric mesenchyme. Nephronectin is localized in the extracellular matrix in the same distribution as the ligand detected by alpha8beta1-AP and forms a complex with alpha8beta1 in vivo. Thus, these results strongly suggest that nephronectin is a relevant ligand mediating alpha8beta1 function in the kidney. Nephronectin is expressed at numerous sites outside the kidney, so it may also have wider roles in development. The approaches used here should be generally useful for characterizing the interactions of novel extracellular matrix proteins identified through genomic sequencing projects.

Alkaline Phosphatase↗
PubMed2001

Local structure of guest molecules in gas hydrates--a model study of Kr and Xe clathrates.

Gas hydrates constitute a class of solids in which small molecules occupy cavities inside an ice-like structure. There is enormous scientific and technological interest in understanding the structure, stability and formation mechanism of clathrates. We developed and constructed a variable temperature high-pressure cell for x-rays measurements, which allows in situ studies of clathrate formation or decomposition. We used XAFS and Diffraction techniques to study the evolution of the structure during formation and decomposition. We studied two clathrates structures, structure I (Xe) and structure II (Kr). We were able to identify the local structure around the guest atom. We identified the rare gas-water complexes that act as precursor to the formation of the crystalline phases. We observed the transformation of the clathrate from structure II to structure I when Xe is added to Kr clathrates.

Journal Article↗
PubMed1999

Localized measurement of kinase activation in oocytes of Xenopus laevis.

We have combined a rapid cytoplasmic sampling technique with capillary electrophoresis to measure the activation of protein kinase C (PKC) in a small region (approximately 60 microm) of a Xenopus oocyte. The phosphorylation of a fluorescent PKC substrate was measured following addition of a pharmacological or physiological stimulus to an oocyte. When substrates for cdc2 kinase (cdc2K), PKC, and protein kinase A (PKA) were comicroinjected into an oocyte, all three substrates could be identified on the electropherogram after cytoplasmic sampling. With this new method, it should be possible to measure simultaneously the activation of multiple different kinases in a single cell, enabling the quantitative dissection of signal transduction pathways.

Amino Acid Sequence↗
PubMed1997

Cytokine gene expression during the elicitation phase of contact sensitivity: regulation by endogenous IL-4.

Recent studies have focused on characterizing the cytokine profile produced in the epidermis during the sensitization phase of contact sensitivity (CS). Some prior studies have also identified altered individual cytokine mRNA profiles in skin or draining lymph nodes (or several cytokine mRNA profiles in the epidermis) during the elicitation phase of CS. In this study we determined the dynamics of appearance of a battery of cytokine mRNA levels in both the epidermis and dermis during the elicitation phase of CS. We isolated mRNA from dispase-separated epidermis and dermis of TNCB-sensitized and naive BALB/c mice at various times after TNCB challenge. Changes in IFN-gamma and IL-4 mRNA levels (by semiquantitative RT-PCR) were more reproducible and dramatic than those of other cytokines studied (IL-1beta, IL-2, IL-10, and IL-12 p40). Compared to naive mice, sensitized mice had significantly elevated IL-4 mRNA signals 9 and 24 h (dermis), and 24 h (epidermis), after TNCB challenge. The increased IL-4 mRNA levels were mast-cell-independent, because sensitized mast-cell-deficient mice showed similar increases in IL-4 mRNA. To examine the role of endogenous IL-4 in CS elicitation, sensitized mice were treated with anti-IL-4 mAb 1 h before challenge. In accord with prior studies, anti-IL-4 mAb-pretreated mice showed increased ear swelling 24 h after challenge compared to mice pretreated with isotype control mAb. Anti-IL-4 mAb pretreatment also enhanced IFN-gamma, IL-2, IL-12 p40, and IL-1beta (but not IL-10) mRNA signals in the dermis of sensitized and challenged mice. These data indicate that IL-4 is produced in murine skin during the elicitation phase of CS and is an important down-modulator of inflammation. IL-4 may blunt CS by regulating local production of proinflammatory cytokines.

Animals↗
PubMed1989

A new murine CD4+ T cell subset with an unrestricted cytokine profile.

CD4+ T cell clones were derived from mice immunized to keyhole limpet hemocyanin to characterize the cytokine profiles of newly isolated clones. Surprisingly, several of the clones had an unrestricted profile, producing IL-2, IL-3, IL-4, IFN-gamma, and TNF after either Con A or Ag stimulation. The coproduction of IL-2 and IL-4 was confirmed at the mRNA level. Subclones were derived which contained RNA transcripts for, as well as secreted, both IL-2 and IL-4 thus confirming the clonality of the original T cell clones. CD4+ T cell clones that expressed an unrestricted cytokine profile upon Con A stimulation were also isolated from mice immunized to other Ag (hen egg lysozyme, OVA, or type II collagen). These data indicate that CD4+ T cell clones newly isolated from immunized mice do not necessarily segregate into the Th1 and Th2 subsets. We propose this new murine CD4+ cell subset with an unrestricted pattern of cytokine production be called Th0.

Animals↗
PubMed1988

The isolation of angiotensin-converting enzyme cDNA.

Angiotensin-converting enzyme (ACE) is an Zn(II)-containing dipeptidyl carboxypeptidase that converts angiotensin I to the potent vasoconstrictor, angiotensin II. Using oligonucleotide probes based on the amino acid sequence of mouse kidney ACE, cDNA encoding this protein has been isolated. One cDNA, ACE.31, encodes the N-terminal 332 amino acids of mouse ACE, a portion of the protein containing a putative 34-amino acid leader sequence and the N terminus of the mature protein. Northern analyses with cloned ACE cDNA revealed that both mouse kidney and lung express two ACE mRNAs, one of 4900 and another of 4150 bases. Southern analysis suggests that cDNA ACE.31 is the product of a single gene, and thus these data add evidence to the hypothesis that the converting enzymes produced by epithelial and endothelial cells are identical.

Amino Acid Sequence↗
PubMed1988

Using the OSCE to measure clinical skills performance in nursing.

The measurement of clinical skills performance continues to pose a challenge for nurse educators. This paper will report on the use of the objective structured clinical examination (OSCE) to measure the psychomotor learning outcomes of a programme designed to assist students to learn to conduct a nursing neurological examination. The OSCE has a tradition in medicine, having been developed by Ronald Harden in Scotland and first reported in the British Medical Journal in 1975. The University of Ottawa has the longest North American experience with this type of evaluation procedure and there is an increasingly rich medical literature referring to the OSCE. Although the OSCE appears to be a promising method for evaluating competence in the performance of clinical skills, there are no studies in the nursing literature examining the use of the OSCE as a method for evaluating the performance of clinical skills by nurses. Our experience suggests that the OSCE may be a powerful tool in the evaluation of clinical competence in nursing and that it may also be an effective facilitator for learning to perform clinical skills in nursing.

Clinical Competence↗
PubMed1983

Respiratory and calcium transport properties of spiny lobster hepatopancreas mitochondria.

Mitochondria were isolated from the hepatopancreas of the Florida spiny lobster Panulirus argus using a high osmolarity medium containing 600 mM mannitol, 83 mM sucrose, 5 mM 4-morpholinepropanesulfonic acid, pH 7.6, 0.5% bovine serum albumin (BSA), and 1 mM EDTA. O2 uptake and Ca2+ transport were measured by electrode methods in similar media (plus 4 mM KPi, 3.3 mM MgCl2, and 0.67 mg/ml BSA, with 80 mM KCl replacing a portion of the osmotic support). Substrate-supported respiration was observed to be coupled to phosphorylation of ADP or uptake of Ca2+ ions. State 3 rates (nanogram atoms O X minute-1 X milligram protein-1 +/- SEM (N)) were: 49.2 +/- 3.9 (19), succinate; 30.9 +/- 3.9 (6), DL-palmitoyl carnitine; 29.0 +/- 2.7(9), L-malate; 40.0 +/- 2.3(3), L-glutamate; 27.7 +/- 2.2(5), D-3-hydroxybutyrate; and 26.4 +/- 2.4 (18), L-proline +/- pyruvate. alpha-Glycerol phosphate was not oxidized. Ca2+ uptake driven by succinate oxidation proceeded with Ca:O ratios of 4.0 +/- 0.2 (SEM). Hepatopancreas mitochondria were not uncoupled by Ca2+ uptake in excess of 1100 ng atoms X mg protein-1. Ca2+ efflux could be induced by ruthenium red, indicating the presence of an active Ca2+ cycle. These mitochondria may provide a favorable model system in which to study regulation of the Ca2+ cycle.

Animals↗
PubMed1983

Metallothionein and occupational exposure to cadmium.

The relationship between metallothionein (MT), chronic exposure to cadmium (Cd), and renal function was investigated in 53 men who were occupationally exposed to Cd. The aim was to determine if MT is a potential biological monitor for chronic exposure to Cd which would be useful for preventing Cd nephropathy. In this study MT excretion, serum MT, and serum creatinine concentrations were significantly higher in subjects with abnormal renal function who had been exposed to Cd. MT excretion was also linearly related on an individual basis to protein excretion, beta 2-microglobulin (beta 2-M) excretion, and cumulative time weighted exposure (dose). MT excretion was also a better predictor of dose than either beta 2-M excretion or Cd excretion. The findings suggest that MT is a potential biological monitor for chronic Cd exposure that would be useful for preventing Cd-induced nephropathy. Further studies of non-specific nephropathies and MT are needed to determine if MT is a specific indicator of proximal tubule function secondary to chronic exposure to Cd.

Adult↗
PubMed1982

Isolation and characterization of the mitochondrial DNA from the florida spiny lobster, Panulirus argus.

1. Mitochondria and mitochondrial DNA were isolated from the digestive gland of Panulirus argus. 2. The mitochondrial DNA has an average contour length of 5.13 microns which corresponds to a molecular weight of 10.10 X 10(6) daltons. 3. The molecular weight based on agarose gel electrophoresis of restricted individual DNA samples ranges from 10.04 to 10.4 X 10(6) daltons. 4. Restriction endonuclease analysis with Bam H1 and Eco R1 demonstrate variation in nucleotide sequence between individual lobsters.

Animals↗