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Biomedical subjects

M E Walker

Publications and source records attributed to M E Walker.

10 recordsLinked to original sources
PubMed1992

Intratracheal aerosolization of endotoxin in the rat: a model of the adult respiratory distress syndrome (ARDS).

A technique is described for the intratracheal aerosolization of endotoxin into the rat. Using a miniaturized nozzle within the tracheal lumen to optimize uniform distribution 0.5 ml of an endotoxin solution (7 mg/kg) was aerosolized and dispersed throughout the lung. Time course studies of pulmonary function and histological changes revealed marked functional and morphological changes by 24 h. Histopathologic changes consisted of widespread pulmonary oedema and a diffuse neutrophilic alveolitis. At the same time, there were significant decreases in tidal volume, minute ventilation and lung compliance. Haematologic changes were also seen, including profound thrombocytopaenia and leukopaenia together with an increased haematocrit, indicating systemic effects in this model. Bronchoalveolar lavage (BAL) at 24 h revealed significant increases in BAL protein, erythrocytes and neutrophils. The functional, cytological and histological changes observed after endotoxin challenge mimic those seen in the Adult Respiratory Distress Syndrome in humans and can thus be used as a model to compare the efficacy of a variety of therapeutic interventions for this syndrome.

Administration, Inhalation↗
PubMed1991

Yeast pyruvate carboxylase: identification of two genes encoding isoenzymes.

In Saccharomyces cerevisiae, pyruvate carboxylase [EC 6.4.1.1] has an important anaplerotic role in the production of oxaloacetate from pyruvate. We report here the existence of two pyruvate carboxylase isozymes, which are encoded by separate genes within the yeast genome. Null mutants were constructed by one step gene disruption of the characterised PYC gene in the yeast genome. The mutants were found to have 10-20% residual pyruvate carboxylase activity, which was attributable to a protein of identical size and immunogenically related to pyruvate carboxylase. Immunocytochemical labelling studies on ultrathin sections of embedded whole cells from the null mutants showed the isozyme to be located exclusively in the cytoplasm. We have mapped the genes encoding both enzymes and shown the previously characterised gene, designated PYC1, to be on chromosome VII whilst PYC2 is on chromosome II.

Chromosome Mapping↗
PubMed1991

Effects of adrenergic antagonists on cocaine-induced changes in respiratory function.

Cocaine-induced changes in respiratory rate (f), tidal volume (VT), total pulmonary ventilation (VE), dynamic lung compliance (Cdyn) and total pulmonary resistance (RL) were measured in anesthetized, spontaneously breathing Sprague-Dawley rats using a whole-body plethysmograph and an esophageal manometer. Carotid arterial pressure and heart rate were simultaneously monitored. An intravenous (i.v.) dose of 10 mg/kg of cocaine was lethal in all rats tested with death resulting from respiratory failure occurring between 0.25 and 1.5 min after dosing. At an i.v. dosage of 5 mg/kg, cocaine was nonlethal, although a reduction in VE was evident during the first minute after dosing. This reduction in VE was due to a decrease in f and the lack of a compensatory increase in VT. A slight decrease in RL also became evident approximately five minutes after dosing. Pretreatment with the nonselective alpha-adrenergic antagonist phentolamine (10 mg/kg) prevented the cocaine-induced depression in VE by reducing the decrease in f and blocking the inhibition of a compensatory increase in VT. In contrast, pretreatment with the nonselective beta-adrenergic antagonist propranolol (1 mg/kg) potentiated the cocaine-induced decrease in VE by enhancing the depression of f. Pretreatment with propranolol also caused a cocaine-dependent decrease in Cdyn. At a dosage of 0.3 mg/kg, labetalol, a compound possessing both nonselective alpha- and beta 1-antagonist activity (1:7) appeared to cause only a minimal potentiation of the cocaine-induced depressions in VE and f. Pretreatment with propranolol or labetalol also resulted in the death of 20% of the rats administered 5 mg/kg of cocaine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1991

Isolation of a yeast mutant deficient in pyruvate carboxylase activity.

To improve our understanding of the catalytic mechanism and regulatory properties of pyruvate carboxylase (EC 6.4.1.1), an important biotin-dependent enzyme, we have sought to isolate mutants in Saccharomyces cerevisiae which are defective in pyruvate carboxylase activity. One mutant was isolated which was unable to grow on glucose minimal medium unless supplemented with aspartate. Although the enzyme had only 25% of the wild type pyruvate carboxylase activity, Western analysis and RNase protection analysis demonstrated that the mutant gene was expressed at approximately 70% of the wild type level. On the basis of genetic crosses and complementation tests, we have attributed the defect to mutations in the PYC gene encoding pyruvate carboxylase.

Base Sequence↗
PubMed1990

Transport of the yeast ATP synthase beta-subunit into mitochondria. Effects of amino acid substitutions on targeting.

We have isolated the yeast ATP2 gene encoding the beta-subunit of mitochondrial ATP synthase and determined its nucleotide sequence. A fusion between the N-terminal 15 amino acid residues of beta-subunit and the mouse cytosolic protein dihydrofolate reductase (DHFR) was transcribed and translated in vitro and found to be transported into isolated yeast mitochondria. A fusion with the first 35 amino acid residues of beta-subunit attached to DHFR was not only transported but also proteolytically processed by a mitochondrial protease. Amino acid substitutions were introduced into the N-terminal presequence of the beta-subunit by bisulphite mutagenesis of the corresponding DNA. The effects of these mutations on mitochondrial targeting were assessed by transport experiments in vitro using DHFR fusion proteins. All of the mutants, harbourin from one to six amino acid substitutions in the first 14 residues of the presequence, were transported into mitochondria, though at least one of them (I8) was transported and proteolytically processed at a much reduced rate. The I8 mutant beta-subunit also exhibited poor transport and processing in vivo, and expression of this mutant polypeptide failed to complement the glycerol- phenotype of a yeast ATP2 mutant. More remarkably, the expression of I8 beta-subunit induced a more general growth defect in yeast, possibly due to interference with the transport of other, essential, mitochondrial proteins.

Amino Acid Sequence↗
PubMed1977

Biochemical genetics of MN.

Quantitative hemagglutination studies of the MN-hemizygous (M/-) patient and his family reported by German et al. are given together with data on the electrophoretic mobility of their red cells. These results, and those obtained on the cells of a donor of the MU phenotype (MU=M+N-S-s-U+); Mu=M+N-S-s-U), demonstrate a series of shortcomings in the current 'precursor transferase' theory of the biochemical genetics of MN antigens. Another theory is proposed, according to which the effects of the MN genes take place exclusively in the protein part of the glycopeptide. The MN proteins would carry acceptor sites for the antigenic oligosaccharides which are put together by enzymes genetically independent of MN. In M glycoproteins, the acceptor sites are close to each other, in doublets, while in N they are all separate. This model is shown to apply successfully to several difficult problems in MN.

Electrophoresis↗
PubMed1976

Linkage of gene for C2 deficiency and the major histocompatibility complex MHC in man. Family study of a further case.

Close linkage between HL-A and C2 deficiency was first reported by FU and co-workers in 1974. We present here a pedigree of a 31-year-old C2-deficient individual with clinical manifestations of Hodgkins disease. The following markers were tested: C2 levels, factor B polymorphism, blood groups, and enzyme typing. In addition to close linkage between HL-A and C2 deficiency, both parents were heterozygous for Bf (HL-A linked, electrophoretic variation of B). The two HL-A haplotypes closely linked to C2 deficiency are different: 2, W18 and W24, W18. They share, however, the SD2 antigen W18 and the LD type 7a.

Adult↗
PubMed1976

Rhmod, a second kindred (Craig).

Three Rhmod siblings were found to have identical Rh: w1, w2, -3, -4, w5 (see article) phenotypes. All had stomatocytic hemolytic anemia. On quantitative hemagglutination studies, as well as on hand tests, all Rh antigens were not equally depressed. Rh17 (Hr0, 'not D') and Rh29 (RH, 'total Rh') were both normal. Rh5 (hr", e) was only slightly depressed. Rh25 (LW) had 50% of the expression expected in normal Rh:-1 cells. Rh1 (Rh0, D), Rh13 (RhA), Rh14 (RhB), Rh15 (RhC), and Rh16 (RhD), were severely depressed. Rh2 (rh', C) was depressed, while Rh7 (rhi, Ce) was absent. Both Rh19 (hrS) and Rh31 (hrB) were depressed. Rh12 (rhG, G) was distinctly depressed, scoring considerably less than rGrG red cells. The unrelated parents, the child of the proposita, and some siblings of each parent showed lessened depression of Rh antigens without displaying the consistent pattern that might be expected from a presumed single suppressor gene. Absence of a consistent pattern may have resulted from differing Rh genotypes, but a frequently observed depression involved Rh14, Rh15, and Rh16 (RhB, RhC, and RhD) without an effect on either Rh1 (RH3 or D) or Rh13 (RhA).

Female↗