Search PubMed⌕ Search

Biomedical subjects

M J Smith

Publications and source records attributed to M J Smith.

At least 145 records · Page 8Linked to original sources
PubMed1996

Effects of fumonisin B1 and (hydrolyzed) fumonisin backbone AP1 on membranes: a spin-label study.

Electron spin resonance (ESR) spectroscopy and spin label techniques have been used to study the effects of fumonisin B1 (FB1) and hydrolyzed fumonisin backbone (AP1) on the structural and dynamic properties of phosphatidylcholine membranes at the molecular level. Multilamellar liposomes consisting of dimyristoylphosphatidylcholine (DMPC) and egg yolk phosphatidylcholine (EYPC) were used. Six different nitroxide spin labels were used to determine what effects FB1 may impart on the ordering and mobility of lipids in membranes. The experimental results disclose the following: (1) In the fluid phase membrane, FB1 significantly increases the fluidities of n-doxylstearic acid (SA) spin labels (SL) attached to carbons 5 and 7, which disorders the alkyl chains and perturbs the surface region of the bilayer; by comparison, minimal effects were detected near the center of the bilayer. (2) In the gel phase, FB1 and AP1 imparts marked rigidifying effects on membrane fluidity, which enlarges the change in ordering on the phase transition even further. (3) FB1 also restricts the mobility of the (rigid) cholestane spin label. (4) A reduction in mobility of the tempo-stearate spin label suggests that the tricarballylic acid (TCA) moieties of FB1 might mimic the structure of polar headgroups in phospholipids. The present results may provide additional mechanisms to elucidate the toxicological activities of the fumonisins.

Dimyristoylphosphatidylcholine↗
PubMed1996

Assembly of microtubule-associated protein tau into Alzheimer-like filaments induced by sulphated glycosaminoglycans.

The paired helical filament (PHF) is the major component of the neurofibrillary deposits that form a defining neuropathological characteristic of Alzheimer's disease. PHFs are composed of microtubule-associated protein tau, in a hyperphosphorylated state. Hyperphosphorylation of tau results in its inability to bind to microtubules and is believed to precede PHF assembly. However, it is unclear whether hyperphosphorylation of tau is either necessary or sufficient for PHF formation. Here we show that non-phosphorylated recombinant tau isoforms with three microtubule-binding repeats form paired helical-like filaments under physiological conditions in vitro, when incubated with sulphated glycosaminoglycans such as heparin or heparan sulphate. Furthermore, heparin prevents tau from binding to microtubules and promotes microtubule disassembly. Finally, we show that heparan sulphate and hyperphosphorylated tau coexist in nerve cells of the Alzheimer's disease brain at the earliest known stages of neurofibrillary pathology. These findings, with previous studies which show that heparin stimulates tau phosphorylation by a number of protein kinases, indicate that sulphated glycosaminoglycans may be a key factor in the formation of the neurofibrillary lesions of Alzheimer's disease.

Alzheimer Disease↗
PubMed1996

Effects of fumonisin B1 on oxygen transport in membranes.

Electron spin resonance (ESR) spin-label oximetry has been used to study the effects of fumonisin B1 (FB1), a sphingoid-like mycotoxin, on oxygen transport in phosphatidylcholine (PC) bilayers. Moreover, the use of spin labels attached to different carbons of fatty acids makes it possible to do structural and oximetric determinations with the same test sample. Specifically, the incorporation of 10 mol% FB1 increased the oxygen transport properties of both saturated and unsaturated membranes at 37 degrees C by ca. 30% and decreased the ordering of the hydrocarbon chains near the surface of the membranes; concomitantly, oxygen transport near the center of bilayers was diminished slightly, and the relative oxygen diffusion-concentration product profile curves were markedly flattened.

Carcinogens, Environmental↗
PubMed1996

Phylogeography of an asexual marine clam complex, Lasaea, in the northeastern Pacific based on cytochrome oxidase III sequence variation.

Northeastern Pacific populations of the intertidal marine clam Lasaea are exclusively composed of polyploid asexual clones that lack pelagic larval development. We investigated the phylogeographic structure of this clonal assemblage by assaying genetic divergence in 4 populations along 2000 km of the west coast of North America. In each population a 462-nt portion of the mitochondrial Cytochrome Oxidase III gene was amplified and sequenced for 30 individuals. A total of 21 haplotypes were detected and phylogenetic analyses resolved this variation into 5 main branches that differ in sequence composition by 8.9-14.5%. Two of the branches each encompass a single haplotype, the other 3 terminate in clades containing 3-11 lineages and within clade divergence ranges from 0.4 to 2.3%. Obvious geographic structuring was evident in that 19 of the 21 lineages were restricted in their distributions to single populations and 3 of the main phylogenetic branches were limited to specific marine biogeographic provinces. Two of the clades were encountered in multiple, geographically distant populations; however, the absence of shared haplotypes indicates that long distance gene flow is rare among these direct-developing populations. Northeastern Pacific Lasaea clones form a robust monophyletic grouping relative to other studied populations of the cosmopolitan genus. We estimate divergence times among northeastern Pacific clones to range from 3 to 6 myr. If the latest common ancestor of these exclusively asexual, genetically diverse, regionally monophyletic Lasaea lineages was also asexual, this represents a minimal age estimate for asexuality in the genus. The most plausible alternate hypothesis requires that at least 5 northeastern Pacific sexual parental species have recently become extinct.

Animals↗
PubMed1996

Molecular phylogeny of eastern Pacific sea cucumbers (Echinodermata: Holothuroidea) based on mitochondrial DNA sequence.

A molecular phylogenetic analysis of some Holothuroidea was undertaken in order to clarify the systematics and taxonomy of this class in the northeast Pacific. DNA sequence for portions of two mitochondrial genes, the large ribosomal subunit and cytochrome oxidase 1 was obtained from 16 species of sea cucumbers, including nine members of the family Cucumariidae. As reported for many mitochondrial genomes, a strong bias against G was noted in the coding strand at synonymous sites. In order to verify trees recovered in the presence of this bias, parsimony, maximum likelihood, distance, and log determinant methods were all employed. The resulting molecular phylogeny of the Cucumariidae, with a few exceptions, supported existing taxonomy which is based largely on the morphology of calcareous parts. In particular, evolutionary relationships among the brooding species were clarified. Our results confirm that C. pseudocurata Deichmann is distinct from C. curata Cowles and that these two species do not represent geographic variants of a single species. In fact C. pseudocurata appears to be conspecific with the more northerly distributed C. vegae Theel. We also clarify the identity of C. lubrica Clark and further suggest that C. fisheri astigmata (recently revised to Pseudocnus) should be considered a junior synonym of C. lubrica. The recent description of C. pallida Kirkendale and Lambert as a species, distinct from C. miniata (Brandt), is also supported. The resultant phylogenetic trees are consistent with multiple origins of direct development within the Cucumariidae. Finally, we suggest that an in-depth phylogenetic analysis of sea cucumber families will require examination of additional, more slowly evolving, regions of the genome(s).

Amino Acid Sequence↗
PubMed1996

Duration of embryonic diapause in the brush-tailed bettong, Bettongia penicillata (Potoroidae): effect of age of quiescent corpus luteum.

It has been shown that changes to the frequency of sucking by the pouch young do not affect the time of reactivation of the quiescent corpus luteum and diapause embryo in Bettongia penicillata; these observations led to the suggestion that the corpus luteum may have an inherent maximum duration of quiescence. The aim of the present study was to investigate the effect of the age of the corpus luteum on the timing of its reactivation. Ovulation fails to occur post partum in female B. penicillata isolated from males, and the introduction of a male B. penicillata induces oestrus in females suckling a young in the pouch. Oestrus was induced from Day 23 of lactation to Day 76, in different females, and the corpus luteum became quiescent. All parturitions occurred between Day 95 and Day 103 of lactation (average, Day 98.8), at the time expected if the corpus luteum had been formed post partum. Duration of quiescence of the corpus luteum ranged from 60 days to 10 days, compared with 83.9 +/- 0.43 days in females that mated post partum. The results show that the age of the corpus luteum does not affect the timing of its redevelopment and release of the embryo from diapause near the end of the period of the young being suckled within the pouch.

Animals↗
PubMed1996

Length variation, heteroplasmy and sequence divergence in the mitochondrial DNA of four species of sturgeon (Acipenser).

The extent of mtDNA length variation and heteroplasmy as well as DNA sequences of the control region and two tRNA genes were determined for four North American sturgeon species: Acipenser transmontanus, A. medirostris, A. fulvescens and A. oxyrhnychus. Across the Continental Divide, a division in the occurrence of length variation and heteroplasmy was observed that was concordant with species biogeography as well as with phylogenies inferred from restriction fragment length polymorphisms (RFLP) of whole mtDNA and pairwise comparisons of unique sequences of the control region. In all species, mtDNA length variation was due to repeated arrays of 78-82-bp sequences each containing a D-loop strand synthesis termination associated sequence (TAS). Individual repeats showed greater sequence conservation within individuals and species rather than between species, which is suggestive of concerted evolution. Differences in the frequencies of multiple copy genomes and heteroplasmy among the four species may be ascribed to differences in the rates of recurrent mutation. A mechanism that may offset the high rate of mutation for increased copy number is suggested on the basis that an increase in the number of functional TAS motifs might reduce the frequency of successfully initiated H-strand replications.

Animals↗
PubMed1996

A comparative analysis of pharmacokinetics of ceftriaxone in serum and pleural fluid in humans: a study of once daily administration by intramuscular and intravenous routes.

Pleural fluid and serum pharmacokinetics of ceftriaxone were performed in thirteen patients with pleural effusion. One gram of ceftriaxone was administered once daily intravenously in six patients and intramuscularly in seven patients. Ceftriaxone concentrations were measured in serum and pleural fluids in both groups on the first day of administration and in four patients of the intramuscular group on the fourth day of administration. The mean serum peak concentration at 1 h was 199 mg/L (S.E.M. 63.2) in the iv group and 80.5 mg/L (S.E.M. 12.0) in the im group. The mean serum trough concentrations in the two groups at 24 h were 27.5 mg/L (S.E.M. 12.6) and 29.7 mg/L (S.E.M. 5.2) respectively. In the pleural fluid, mean peak concentration was 20.1 mg/L (S.E.M. 4.7) at 6 h in the iv group and 15.3 mg/L (S.E.M. 5.1) at 12 h in the im group. The mean trough concentration was 9.6 mg/L (S.E.M. 1.9) and 13.3 mg/L (S.E.M. 3.1) at 24 h in the two groups respectively. On the fourth day of intramuscular administration the serum and pleural fluid peak and trough concentrations were higher when compared with the first day, consistent with a cumulative effect. The serum and pleural fluid concentrations of ceftriaxone following intravenous and intramuscular administration were well above the MIC90 of most common respiratory pathogens indicating good penetration into extracellular spaces. Further, these serum and pleural fluid antibiotic concentrations could be maintained even after a single intramuscular injection of the drug, thus indicating its usefulness as a parenteral mode of therapy on a domicilliary basis with a significant cost-saving potential. In conclusion, intramuscular administration of ceftriaxone would appear to be a convenient method of administering parenteral therapy in lower respiratory tract infections in the hospital and community, with pharmacokinetics very similar to those exhibited by the intravenous route.

Adult↗
PubMed1996

Detection and quantitation of melanoma cells in the circulation of patients.

A method for the quantitation of tyrosinase mRNA in the bloodstream of melanoma patients has been developed by using competitive polymerase chain reaction (PCR) with a heterologous DNA (PCR MIMIC) as an internal standard. The method was validated by demonstration of similar amplification efficiencies for both molecules and by accurate quantitation of an artificial fourfold difference in the level of tyrosinase mRNA. The ratio of amplified target to amplified standard (At/As ratio) was determined for a range of melanoma patients who had previously tested positive for tyrosinase. Sequential samples were also analysed to examine the level of tyrosinase in individual patients over time. When tyrosinase levels in melanoma cell lines were compared for a constant amount of total RNA, or for a constant number of cells, tyrosinase mRNA was found to vary more than a thousand-fold between cell lines. Because of this, the At/As ratio of patients was compared with the At/As ratios obtained when 10-fold serial dilutions of cells from a control melanoma cell line (MM200) were added to 2 ml of packed blood. An 'MM200 equivalence' value was thus calculated, giving the equivalent number of MM200 cells in the bloodstream of melanoma patients. Prolonged follow-up will be needed to determine the prognostic significance of the detection and levels of tyrosinase mRNA in the bloodstream of melanoma patients.

Adult↗
PubMed1996

Atropine Metabolism by Pseudomonas sp. Strain AT3: Evidence for Nortropine as an Intermediate in Tropine Breakdown and Reactions Leading to Succinate.

Pseudomonas strain AT3, isolated by elective culture with atropine, hydrolyzed atropine and grew diauxically, first on the tropic acid and then on the tropine. Tropine was also used as a sole carbon and energy source. The methyl group of tropine was eliminated as formaldehyde, and the nortropine thus formed was a precursor of 6-hydroxycyclohepta-1,4-dione. Ammonia was detected as a product of nitrogen elimination. 6-Hydroxycyclohepta-1,4-dione was oxidized to cyclohepta-1,3,5-trione by an induced NAD(sup+)-specific dehydrogenase. Although cyclohepta-1,3,5-trione is a (beta)-diketone with two potential hydrolytic cleavage sites, an induced hydrolase was specific for one of these sites, with 4,6-dioxoheptanoate as the only hydrolysis product. Unlike the alternative cleavage product (3,6-dioxoheptanoate), this compound is also a (beta)-diketone, and a second hydrolytic cleavage formed succinate and acetone. Although Pseudomonas strain AT3 was not capable of growth with acetone, the compound was not detected in the culture medium and may have been lost to the atmosphere. Exhaustive experimentation with a wide range of conditions did not result in detection of the enzymes required for cleavage of the carbon-nitrogen bonds leading to the formation of nortropine and 6-hydroxycyclohepta-1,4-dione.

Journal Article↗
PubMed1996

Roles of prostaglandins and nitric oxide in the effect of endothelin-1 on renal hemodynamics.

It is known that endothelin-1 stimulates the release of nitric oxide and prostaglandins in various vascular beds. We designed the present study to analyze the roles of prostaglandins and nitric oxide in the effect of endothelin-1 on the regulation of renal hemodynamics and renin release. We used N omega-nitro-L-arginine methyl ester (L-NAME) and meclofenamic acid to inhibit the production of nitric oxide and prostaglandins, respectively. With a nonfiltering kidney model, renal blood flow was reduced 21% in dogs treated with L-NAME and 18% in dogs treated with meclofenamic acid. Inhibition of nitric oxide and prostaglandins, however, produced opposite effects on estimated glomerular hydraulic pressure: L-NAME increased glomerular hydraulic pressure from 63.1 +/- 0.9 to 64.6 +/- 1.3 mm Hg (P < .01), and meclofenamic acid reduced glomerular hydraulic pressure from 63.3 +/- 1.4 to 59.8 +/- 1.6 mm Hg (P < .01). Endothelin-1 infusion produced a dose-dependent reduction in renal blood flow after blockade of nitric oxide and prostaglandins. The responses of glomerular hydraulic pressure were different in the two groups during endothelin-1 infusion. Endothelin-1 progressively reduced glomerular hydraulic pressure in a dose-dependent fashion in the meclofenamic acid group. However, endothelin-1 slightly increased glomerular hydraulic pressure until the infusion rate reached 5.0 ng/kg per minute. At that rate, endothelin-1 reduced glomerular hydraulic pressure from 63.3 +/- 1.4 to 47.0 +/- 1.4 mm Hg in the meclofenamic acid group (P < .01), a more than 25% reduction, whereas at the same dose, endothelin-1 reduced glomerular hydraulic pressure only less than 2% in the L-NAME group. In addition, blockade of nitric oxide and prostaglandins did not alter the inhibitory effect of endothelin-1 on renin release in the non-filtering kidney. Therefore, the present study demonstrates that the release of nitric oxide and prostaglandins might modulate the effects of endothelin-1 on the renal circulation. The present findings suggest that the differential vasoconstrictive effects of endothelin-1 on preglomerular and postglomerular vessels are associated with its stimulation of nitric oxide and prostaglandin production.

Animals↗
PubMed1996

PTL-1, a microtubule-associated protein with tau-like repeats from the nematode Caenorhabditis elegans.

Tau, MAP2 and MAP4 are structural microtubule-associated proteins (MAPs) that promote the assembly and stability of microtubules. They share three or four imperfect tandem repeats of an amino acid motif, which is involved in the binding to microtubules. All sequences to data containing this motif are of mammalian origin. We report here the cloning and functional characterisation of a new member of this family of proteins from the nematode Caenorhabditis elegans. This protein exists as two isoforms of 413 and 453 amino acids with four or five tandem repeats that are 50% identical to the tau/MAP2/MAP4 repeats. Both isoforms bind to microtubules and promote microtubule assembly, with the five-repeat isoform being more effective at promoting assembly than the four-repeat isoform. When expressed in COS cells, the five-repeat isoform co-localises with microtubules and induces the formation of microtubule bundles, whereas its expression in Sf9 cells leads to the extension of long unipolar processes. In view of its length, amino acid sequence and functional characteristics, we have named this invertebrate structural MAP 'Protein with Tau-Like Repeats' (PTL-1). In C. elegans PTL-1 is expressed in two places known to require microtubule function. It is first seen in the embryonic epidermis, when circumferentially oriented microtubules help to distribute forces generated during elongation. Later, it is found in mechanosensory neurons which contain unusual 15 protofilament microtubules required for the response to touch. These findings indicate that MAPs of the tau/MAP2/MAP4 family are found throughout much of the animal kingdom, where they may play a role in specialised processes requiring microtubules.

Amino Acid Sequence↗
PubMed1996

Nursing students' perspectives: experiences of caring and not-so-caring interactions with faculty.

The purpose of this study was to describe the meaning of baccalaureate nursing students' lived experience of caring and not-so-caring interactions with faculty. The research questions explored the phenomenon of being cared-for or not-cared-for by asking, "What does being cared-for by faculty mean to baccalaureate nursing students?" Students were also asked to describe not-so caring interactions with faculty. Seventeen baccalaureate nursing students at a private liberal arts college and 15 baccalaureate nursing students at a public university were interviewed. Transcripts of the tape-recorded interviews were analyzed using Giorgi's technique. After reflection upon the content of the interviews, significant statements were identified, meaning units were developed, and themes were extracted which were then abstracted into categories of Recognition, Connection, and Confirmation/Affirmation. Finally, general structural descriptions of phenomena of a caring and of a not-so-caring interaction were constructed. Implications for teaching, research, and practice are described.

Adult↗
PubMed1996

The association between parental smoking and the diet quality of low-income children.

OBJECTIVE: To assess the association between parental smoking and the diet quality of children residing in low-income housholds in the United States. MTHODS: Data from 515 low-income children (less than or equal to 185% of the poverty line), ages 2 to 17, who participated in the 1989 and 1990 United States Department of Agriculture Continuing Survey of Food Intakes of Individuals were examined. Diet quality was assessed by examining the average daily amount of nutrients consumed per 1000 kcal for protein, fiber, and 14 essential vitamins and minerals as well as total energy, percent of energy from total fat and saturated fat, and cholesterol and sodium intakes using the 3-day average of one 24-hour recall and 2 days of diet records. Parental smoking was categorized as four levels (nonsmoker; 1 to 10, 11 to 20, and more than 20) on the basis of the average number of cigarettes smoked per day by the sample child's parents. Analysis of covariance examined differences in the children's nutrient intake among the four smoking categories while controling for race, mother's age and occupation, child age, and sex. RESULTS: Low-income children with parents who smoked (n = 235) were more likely to be white (P <.001), had younger mothers (P <.05) and were more likely to have mothers employed in blue-collar occupations (P <.001) than children whose parents were nonsmokers (N = 280). Children whose parents smoked more than 20 cigarettes per day had a higher level of energy from saturated fat, and children whose parents smoked 11 to 20 cigarettes per day had the highest cholesterol intakes in comparison with the rest of the sample. Parental smoking was also related to total fiber intake per 1000 kcal, with children of smokers having lower fiber intakes than children of nonsmokers. CONCLUSIONS: On average, low-income children of smokers had a poorer diet quality than low-income children of nonsmokers, thus increasing their future risk of chronic disease.

Adolescent↗