Biomedical subjects
Publications and source records attributed to B Chapman.
Echo-planar imaging (EPI), a distinctive variant of nuclear magnetic resonance, needs only a fraction of a second for an image to be acquired and so is free from movement artifacts caused by respiration or heart beat. Clinical findings in the lungs, heart, and mediastinum of three children with high respiratory and heart rates who were examined by EPI are described.
We have determined the sequence of 2400 base pairs upstream from the human pseudo alpha globin (psi alpha) gene, and for comparison, 1100 base pairs of DNA within and upstream from the chimpanzee psi alpha gene. The region upstream from the promoter of the psi alpha gene shows no significant homology to the intergenic regions of the adult alpha 2 and alpha 1 globin genes. The chimpanzee gene has a coding defect in common with the human psi alpha gene, showing that the product of this gene, if any, was inactivated before the divergence of human and chimpanzee. However the chimpanzee gene contains a normal ATG initiation codon in contrast to the human gene which has GTG as the initiation codon. The psi alpha genes of both human and chimpanzee are flanked by the same Alu family member. The structure and position of this repeat have not been altered since the divergence of human and chimpanzee, and it is at least as well conserved as its immediate flanking sequence. Comparing human and chimpanzee, the 300 bp Alu repeat has accumulated only two base substitutions and one length mutation; the adjacent 300 bp flanking region has accumulated five base substitutions and twelve length mutations.
We report the presence of two separate macromolecular complexes between an immunoglobulin and alkaline phosphatase (EC 3.1.3.1) in the serum of a patient with cholestatic liver disease. The complexes were seen as slow-moving bands on electrophoresis on polyacrylamide gel (70 g/L). Estimates of relative molecular mass for the two bands were 785 000 and 490 000 by gel chromatography on Sephacryl S300, and 640 000 and 420 000 by gradient gel-electrophoresis. Inhibitor and heat-inactivation studies showed that the two bands had similar properties, resembling the liver isoenzyme but more heat stable. Immunological studies suggested that both bands consisted of a complex of liver alkaline phosphatase with kappa type immunoglobulin A.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
1. The aim of this work was to discover the location of the enzymes that convert phosphoenolpyruvate to fructose 6-phosphate during gluconeogenesis in fatty seeds. Cotyledons of 5-day-old dark-grown seedlings of marrow (Cucurbita pepo) were used as experimental material. 2. Cotyledons were separated into palisade and mesophyll tissue. Extracts of the two tissues had comparable activities of gluconeogenic enzymes. 3. Extracts of cotyledons were fractionated by density gradient centrifugation to yeild mitochondria and glyoxysomes, and by gel filtration to yield proplastids. The isolated organelles retained their characteristic ultrastructure and appreciable amounts of marker enzymes. The proportions of the total activities of phosphoglyceromutase and fructose-1, 6-diphosphatase recovered in the mitochondrial and glyoxysomal preparations were insignificant. The same was true for the activities of phosphoglyceromutase and phosphopyruvate hydratase found in the proplastid preparations. 4. Extracts of a number of other gluconeigenic plant tissues were centrifuged at 2500 times g to yield particulate preparations. None of these preparations contained a significant proportion of the total activity of phosphoglyceromutase. 5. It is suggested that gluconeogenesis from phosphoenolpyruvate in plants occurs in the cytoplasm.
Using an in vitro rabbit pancreas system, we studied the effect of monoamine oxidase (MAO) inhibitors on flucose-stimulated insulin secretion. We evaluated the effect of both brief (15 min) and prolonged (60 min) exposure of pancreas segments to non-hydrazine (harmine, alpha-methyltryptamine, tranylcypromine and pargyline) and hydrazine (phenelzine, nialamide, iproniazid) type MAO inhibitors. All of the hydrazine type MAO inhibitors potentiated glucose-stimulated insulin secretion. Of the non-hydrazine inhibitors, only harmine and alpha-methyltryptamine potentiated glucose-stimulated insulin secretion. Hydrazine, although not itself an MAO inhibitor, also potentiated insulin secretion. Sixty minutes of exposure to tranylcypromine or alpha-methyltryptamine caused a decrease in insulin secretion. These MAO inhibitors are primary amines and primary amines can inhibit insulin secretion. The dopamine (DA) or serotonin (5-HT) content of the B-cells was increased by incubating rabbit pancreas with L-3, 4-dihydroxyphenylalanine (L-Dopa) or 5-hydroxytryptophan (5-HTP) for forty-five minutes prior to stimulation with glucose. Non-hydrazine MAO inhibitors increased dopamine inhibition of insulin secretion and either did not alter, or decreased serotonin inhibition of insulin secretion. Rabbit pancreatic islets were isolated using the collagenase digestion technique. The MAO activity of islet homogenates was determined using 5-HT and DA as substrates. Rabbit islet MAO has only one-tenth the specific activity against 5-HT (35 +/- 8.7 mumumoles/mg/min, M +/- SEM) that it has against DA (357 +/- 62.3 mumumoles/mg/min). This suggests that one reason that MAT inhibitors do not increase serotonin inhibition of insulin secretion is because MAO is not the major pathway for 5-HT inactivation in rabbit pancreatic islets. These studies suggest that MAO inhibitors alter insulin secretion, by both decreasing B-cell monoamine degradation and by mechanisms that do not involve MAO inhibition.
Monoamine oxidase (MAO) is present in isolated islets of Langerhans of rabbits, golden hamsters, and rats. Tryptamine, tyramine, serotonin, and dopamine can serve as substrates for this enzyme. We compared the properties of islet and liver MAO in the rabbit. The Michaelis constant (K(m)) for tryptamine of islet MAO (6.5 times 10-5M) is greater than the K(m) of liver MAO (3 times 10-5M). The K(m) for tyramine of islet MAO (1.5 times 10-4M) is similar to the K(m) of liver MAO (1.8 times 10-4M). Islet MAO appeared to be more susceptible to heat inactivation (50 degrees C) than did liver MAO. This may be an artifact produced by the collagenase technique used in the preparation of the islets, as collagenase treatment of liver increased the thermal lability of the MAO in this tissue. Liver and islet MAO have a comparable sensitivity to MAO inhibitors such as clorgyline, deprenyl, tranylcypromine, pargyline, and harmine. The present report, along with previous reports that MAO inhibitors alter insulin secretion, suggests that islet MAO may modify insulin secretion.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
In this report we describe some modifications of the collagenase digestion technique for the preparation of pancreatic islets, that we have found helpful in preparing isolated islets of Langerhans from rabbits and hamsters. These modifications include disrupting the pancreatic acinar tissue by directly infiltrating it with Hanks' solution, periodically monitoring the progress of the collagenase digestion of the pancreatic tissue with the dissecting microscope, and purifying the islets by serial passage of the digested tissue through three Petri dishes containing Hanks' solution. This technique results in the successful isolation of the fragile and irregular rabbit islets as well as the isolation of the sturdier and more uniformly shaped hamster islets. The isolated respond to a glucose stimulus with an increase in radioimmunoassayable insulin secretion. We also describe a filtration technique for the preparation of isolated islets for histological examination. Isolated islets are retained on Millipore filters. The filters are then fixed, stained and mounted. Finally, we present realistic photographs of rabbit and hamster islets, as they appear under the dissecting microscope, during various stages of purification and isolation.
Monocular lid suture during the sensitive period early in the life of a kitten disrupts normal development of inputs from the two eyes to the visual cortex, causing a decrease in the fraction of cortical cells responding to the deprived eye. Such an ocular dominance shift has been assumed to depend on patterned visual experience, because no change in cortical physiology is produced by inequalities between the two eyes in retinal illumination or temporally modulated diffuse light stimulation. A higher-level process, involving gating signals from areas outside striate cortex, has been proposed to ensure that sustained changes in synaptic efficacy occur only in response to behaviourally significant visual inputs. To test whether such a process is necessary for ocular dominance plasticity, we treated 4-week-old kittens with visual deprivation and monocular tetrodotoxin (TTX) injections to create an imbalance in the electrical activities of the two retinas in the absence of patterned vision. After 1 week of treatment we determined the ocular dominance distribution of single units in primary visual cortex. In all kittens studied, a significant ocular dominance shift was found. In addition to this physiological change, there was an anatomical change in the lateral geniculate nucleus, where cells were larger in laminae receiving input from the more active eye. Our results indicate that patterned vision is not necessary for visual cortical plasticity, and that an imbalance in spontaneous retinal activity alone can produce a significant ocular dominance shift.