Biomedical subjects

A G Miller

Publications and source records attributed to A G Miller.

At least 19 recordsLinked to original sources

PubMed1996

Junctional permeability measurements in the embryonic chick lens.

The purpose of this paper is two-fold: to measure junctional permeability of different types of dissociated lens cells and to compare the junctional permeability of dissociated lens cells to that of cells in the intact lens. Dissociated embryonic chick lens cells and intact embryonic chick lenses were loaded with the fluorescent dye 5,6 carboxyfluorescein diacetate. The return of fluorescence after bleaching an individual cell was used to estimate cell-to-cell permeability. Use of the confocal microscope facilitated quantitation of the return of fluorescence as well as optical sectioning needed to measure cell-to-cell permeability in an intact lens. Two types of dissociated cells were studied: spherical and short elongated cells. The average rate constant for 5,6 carboxyfluorescein transfer between these cells was 7.9 x 10(-3) sec-1 and 8.1 x 10(-3) sec-1, respectively. The junctional permeability for both types of cells was reduced by lowering internal pH to 6.0 by bathing the cells in a sodium acetate solution. Permeability measurements of the central epithelial cells of an isolated whole lens gave an average rate constant of 2.6 x 10(-3) sec-1, comparable to the rates measured in the dissociated cells. These results establish that the photobleach method can be used in intact lens to quantitatively assess junctional permeability and that dissociated epithelial cells have very nearly the same junctional permeabilities as cells in the intact lens.

Animals↗

PubMed1996

Conversion of a delayed rectifier K+ channel to a voltage-gated inward rectifier K+ channel by three amino acid substitutions.

Single, double, and triple mutations progressively shift Shaker activation to more hyperpolarized potentials, resulting in an increase in the fraction of inactivated channels at negative resting voltages. The most negatively shifted mutation, the triple mutant, behaves like an inward rectifier. What is usually considered activation of an inward rectifier is, for the triple mutant, recovery from inactivation, and what is usually considered deactivation is inactivation. This conversion from outward rectifier to inward rectifier does not rely on a difference in sign or direction of charge movement of the voltage sensor, since activation of the Shaker outward rectifier is due to a different gate than activation of the triple mutant inward rectifier. Other voltage-dependent inward rectifiers in the Shaker family may work by a similar mechanism.

Amino Acid Sequence↗

PubMed1996

Placental weight, birth measurements, and blood pressure at age 8 years.

OBJECTIVE: To examine relationships between blood pressure during childhood and both placental weight and body size at birth, in an Australian population. DESIGN: A follow up study of a birth cohort, undertaken when cohort members were aged 8 years. SETTING: Adelaide, South Australia. SUBJECTS: 830 children born in the Queen Victoria Hospital in Adelaide, South Australia, during 1975-6. MAIN OUTCOME MEASURES: Systolic and diastolic blood pressure measured when the children were aged 8 years. RESULTS: Blood pressure at 8 years was positively related to placental weight and inversely related to birth weight, after adjusting for the child's current weight. For diastolic pressure there was a decrease of 1.0 mm Hg for each 1 kg increase in birth weight (95% confidence interval (CI) = -0.4 to 2.4) and an increase of 0.7 mm Hg for each 100 g increase in placental weight (95% CI = 0.1 to 1.3). Diastolic pressure was also inversely related to chest circumference at birth, independently of placental weight, with a decrease of 0.3 mm Hg for each 1 cm increase in chest circumference (95% CI = 0.2 to 0.5). CONCLUSIONS: These findings are further evidence that birth characteristics, indicative of fetal growth patterns, are related to blood pressure in later life.

Anthropometry↗

PubMed1995

Family nurse practitioner clinical competencies in alcohol and substance use.

The prevalence of substance use among patients presenting to primary health care settings mandates clinical competency in the area for nurse practitioners (NPs). An educational intervention with an evaluation component is described. The effect of incorporating substance use content into a Family Nurse Practitioner (FNP) curriculum was tested with a convenience sample of 16 FNP students and 8 practicing NPs. Students' knowledge increased significantly; however, differences in students' and practicing NPs' knowledge did not reach significance. Students' clinical competency increased significantly, as demonstrated by standardized patient clinical evaluations, and was significantly better than the practicing NPs in the skill domains of evaluation and record keeping. Educational intervention can improve NP identification of substance-abusing patients in primary health care settings.

Alcoholism↗

PubMed1994

Diurnal urinary volume and uranium output in uranium workers and unexposed controls.

Volume and uranium content were determined in individual urine voids over a 76-h (3.25-d) period from six unexposed normal male subjects and three male uranium workers. Uranium analyses were accomplished by a newly developed high-precision kinetic phosphorescence analysis technique with a lower level of detection of 0.007 ng mL-1. Urinary uranium concentrations in individual voids varied by a factor of 2 or less for any one unexposed subject, although there was an order of magnitude variation among the group of unexposed men. The fractional urinary volume excreted in the "standard" so-called simulated 24-h sample was the same for both the unexposed and exposed groups and averaged 0.42 +/- 0.13 of the total daily urine volume. The fraction of uranium in the simulated 24-h samples was 0.43 +/- 0.15 in the unexposed group but only 0.31 +/- 0.13 in the uranium worker group, suggesting that the use of the simulated 24-h urine sample would underestimate the total daily urinary uranium output by approximately a factor of 2 in the uranium workers. Daily urinary excretion relative to intake from drinking water (essentially equal to the gastrointestinal uptake fraction) among the unexposed group ranged from 0.002-0.028, averaging 0.011 +/- 0.008, with an indication that the gastrointestinal uptake factor was inversely proportional to total intake via drinking water.

Adult↗

PubMed1992

Single-membrane and cell-to-cell permeability properties of dissociated embryonic chick lens cells.

Ion channels are believed to play an important role in the maintenance of lens transparency. In order to ascribe junctional and nonjunctional permeability properties to specific lens cell types, embryonic chick lenses were enzymatically dissociated into cell clusters, cell pairs and single cells, and both cell-to-cell and single-membrane permeability properties were characterized with the patch-clamp technique. Double patch-clamp experiments and single patch-clamp experiments with Lucifer yellow in the pipette demonstrated that the cells in the dissociated preparation were well coupled, the average conductance between pairs being 42 +/- 27 nS. Double patch-clamp experiments also revealed single cell-to-cell channel events with a predominant unitary conductance of 286 +/- 38 pS. Whole-cell measurements of surface membrane conductance indicate heterogeneity within the population of dissociated embryonic chick lens cells: 63% of the cells have a voltage-independent leak current, 14% of the cells have a potassium-selective inward-rectifier current, and 23% of the cells have a current which turns off with positive voltage on a time scale on the order of seconds. The time constant for this turnoff is voltage dependent.

Animals↗

PubMed1989

Placenta praevia--a review with emphasis on the role of ultrasound.

Considerable confusion exists in the literature as a result of the wide range of classification systems for placenta praevia (PP) and low-lying placenta. The discrepancy between frequency of low-lying placentas in the second trimester and PP at term reflects to a certain extent the lack of understanding of the anatomy and physiology of the pregnant uterus. It seems that 'placental conversion' is a real phenomenon and is probably due to the differential growth rates of the placenta and uterus. Maternal bladder overdistension and myometrial contractions account for only a small part of the discrepancy. Diagnostic ultrasound obviously has an important role in placental localization. The role of Magnetic Resonance Imaging remains to be determined. The management of patients with low-lying placenta diagnosed in the second trimester, and the frequency of repeat scans is determined largely by the management protocol of the attending obstetrician.

Female↗

PubMed1986

Effects of dietary alteration of bicarbonate and magnesium on rat bone.

To study the effects of bicarbonate and magnesium on bone, mild acidosis and/or hypermagnesemia were produced in growing rats by feeding ammonium chloride and/or magnesium sulfate. Bone composition, quantitative histomorphometry, and mineral x-ray diffraction (XRD) characteristics were measured after 6 wk of treatment. The results demonstrated that both acidosis (decreased HCO3) and hypermagnesemia inhibited periosteal bone formation, and, when combined, results were summative; and the previously observed in vitro role of HCO3- and Mg2+ as inhibitors of crystal growth were confirmed in vivo. XRD measurements demonstrated that decreased plasma HCO3 resulted in larger crystals and increased Mg resulted in smaller crystals. However, the combined XRD effects of acidosis and hypermagnesemia resembled acidosis alone. It is postulated that the final composition and crystal structure of bone are strongly influenced by HCO3- and Mg2+, and the effects are mediated by the combined influence on both osteoblastic bone formation and the growth of hydroxyapatite.

Animals↗

PubMed1984

Biochemical and genetic analysis of variant mouse hepatoma cells which overtranscribe the cytochrome P1-450 gene in response to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Using the fluorescence-activated cell sorter, we have isolated a population of variant mouse hepatoma cells which have a markedly increased ability to metabolize benzo(a)pyrene. Compared with wild-type (Hepa 1c1c7) cells, the variant cells exhibit increased aryl hydrocarbon hydroxylase activity and increased responsiveness of the aryl hydrocarbon hydroxylase induction mechanism to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Cell fusion experiments indicate that the variant phenotype is co-dominant with respect to wild-type. Filter hybridization analyses indicate that increased accumulation of cytochrome P1-450-specific mRNA accounts for the overproduction of aryl hydrocarbon hydroxylase activity. Measurements of RNA synthesis in isolated nuclei reveal that the variants exhibit an increased rate of transcription of the cytochrome P1-450 gene in response to TCDD. The variant cells contain no detectable alteration in their TCDD receptors, nor is the cytochrome P1-450 gene amplified in the variants. Filter hybridization analyses of restriction endonuclease-digested DNA indicate that the variant cytochrome P1-450 gene is relatively undermethylated, compared with the wild-type gene. We conclude that the variant cells contain an altered cis-acting genomic element(s) which regulates the expression of the cytochrome P1-450 gene.

Animals↗

PubMed1984

Na+ requirement for growth, photosynthesis, and pH regulation in the alkalotolerant cyanobacterium Synechococcus leopoliensis.

We have found that Na+ is required for the alkalotolerance of the cyanobacterium Synechococcus leopoliensis. Cell division did not occur at any pH in the absence of Na+, but cells inoculated into Na+-free growth medium at pH 6.8 did continue metabolic activity, and over a period of 48 h, the cells became twice their normal size. Many of these cells remained viable for at least 59 h and formed colonies on Na+ -containing medium. Cells grown in the presence of Na+ and inoculated into Na+ -free growth medium at pH 9.6 rapidly lost viability. An Na+ concentration of ca. 0.5 milliequivalents X liter-1 was required for sustained growth above pH 9.0. The Na+ requirement could be only partially met by Li+ and not at all by K+ or Rb+. Cells incubated in darkness in growth medium at pH 6.8 had an intracellular pH near neutrality in the presence or absence of Na+. When the external pH was shifted to 9.6, only cells in the presence of Na+ were able to maintain an intracellular pH near 7.0. The membrane potential, however, remained high (-120 mV) in the absence or presence of Na+ unless collapsed by the addition of gramicidin. Thus, the inability to maintain a neutral intracellular pH at pH 9.6 in the absence of Na+ was not due to a generalized disruption of membrane integrity. Even cells containing Na+ still required added Na+ to restore photosynthetic rates to normal after the cells had been washed in Na+ -free buffer at pH 9.6. This requirement was only partially met by Li+ and was not met at all by K+, Rb+, Cs+ Mg2+, or Ca2+. The restoration of photosynthesis by added Na+ occurred within 30 s and suggests a role for extracellular Na+. Part of our results can be explained in terms of the operation of an Na+/H+ antiporter activity in the plasma membrane, but some results would seem to require other mechanisms for Na+ action.

Chlorophyll↗

PubMed1983

Biochemical and genetic analysis of variant mouse hepatoma cells defective in the induction of benzo(a)pyrene-metabolizing enzyme activity.

We have analyzed wild type mouse hepatoma (Hepa 1c1c7) cells and variant cells which are defective in the induction of benzo(a)pyrene-metabolizing enzyme activity. One type of variant has no detectable basal or inducible aryl hydrocarbon hydroxylase activity. This class contains apparently normal cytosolic receptors for 2,3,7,8-tetrachlorodibenzo-p-dioxin, but is unable to translocate the inducer-receptor complex to the nucleus. The second type of variant has low levels of basal and inducible aryl hydrocarbon hydroxylase activity. This class contains cytosolic receptors which are decreased either in their number or in their ability to bind 2,3,7,8-tetrachlorodibenzo-p-dioxin; translocation of the inducer-receptor complex to the nucleus is apparently normal. Cell fusions indicate that both variant phenotypes are recessive with respect to wild type. Complementation analyses indicate that the defects are located on different genes.

Animals↗

PubMed1983

Ethylated fluoresceins: assay of cytochrome P-450 activity and application to measurements in single cells by flow cytometry.

Four ethylated derivatives of fluorescein were synthesized and their metabolism by mouse liver homogenates and cultured mouse hepatoma cells was investigated. Two of the ethylfluoresceins are specifically metabolized by the polycyclic aromatic hydrocarbon inducible cytochrome P-450 to yield fluorescein, which is about 15 times more fluorescent than the ethylated compounds. One of these fluorogenic derivatives, ethoxyfluorescein ethyl ester, is useful for flow cytometric analysis and sorting of intact, viable cells on the basis of cytochrome P-450 activity. The structure-activity relationship of the ethylfluoresceins is discussed.

Animals↗

PubMed1982

Efficient metabolism of benzo(a)pyrene at nanomolar concentrations by intact murine hepatoma cells.

We have studied the metabolism of benzo(a)pyrene (BP) by intact mouse hepatoma cells, at nM concentrations of the carcinogen, using an assay in which we directly measure the rate of BP fluorescence disappearance. The rate of BP metabolism is half-maximal, at limiting cell dilution, when the concentration of BP is about 4 nM. This apparent Km for BP metabolism is much lower than those reported previously for several reasons. (a) Partitioning of BP into cells markedly influences kinetic measurements, and we account for these effects. (b) Enzyme inducers can competitively inhibit BP metabolism and thus may introduce artifacts into kinetic measurements. (c) Under the conditions of this assay, phenolic BP metabolites are produced but do not accumulate, due to their further metabolism; therefore, assays of BP metabolism which measure the production of phenols, such as the commonly used aryl hydrocarbon hydroxylase assay, may markedly underestimate the rate of BP metabolism when intact cells and low substrate concentrations are used. Our results show that cells can efficiently metabolize BP when exposed to BP concentrations similar to those present in the environment.

Animals↗

PubMed1982

Syncope.

Explore the source record for details and available documents.

Dental Care↗

PubMed1981

Novel variants in benzo(a)pyrene metabolism. Isolation by fluorescence-activated cell sorting.

We have used the fluorescence-activated cell sorter to measure the metabolism of the carcinogenic polycyclic aromatic hydrocarbon, benzo(a)pyrene (BP), in individual, viable mouse hepatoma (Hepa 1c1c7) cells and to physically select variants with either markedly elevated or markedly decreased ability to metabolize to low, nontoxic concentrations of BP (25 nM) and measuring the rate of disappearance of BP fluorescence. We show by several criteria that the disappearance of BP fluorescence is due to the metabolism of the carcinogen. Cells sorted according to their rae of loss of BP fluorescence exhibit the predicted phenotypes in BP-metabolizing activity, as measured by the aryl hydrocarbon hydroxylase assay.

Animals↗

PubMed1981

Fixation of porous titanium implants in cortical bone enhanced by electrical stimulation.

The effect of in vivo electrical stimulation on the interfacial strength between porous titanium implants and cortical bone was studied in mongrel dogs. The interfacial shear strength of the stimulated implants was consistently greater than that of controls. No difference could be observed in the quality of bone ingrowth. The data suggest that the rate and quantity of bone ingrowth were enhanced by electrical stimulation.

Animals↗

PubMed1980

Normal maturational changes in bone matrix, mineral, and crystal size in the rat.

Normal rat bone maturation has been studied using biochemical methods and hydrazine separation of matrix and mineral for X-ray diffraction. In the bone, the amount of mineral increases between 4 and 22 weeks of age, while in the matrix, the ratio of noncollagenous protein to collagen progressively decreases. In mineral, in the absence of serum ion changes, growth in mean crystal size appears to be the determinant of the changing ratios of calcium, magnesium, carbonate, and phosphorus, and of the increasing mineral density.

Aging↗

PubMed1980

Active transport and accumulation of bicarbonate by a unicellular cyanobacterium.

The rates of inorganic carbon accumulation and carbon fixation in light by the unicellular cyanobacterim Coccohloris peniocystis have been determined. Cells incubated in the light in medium containing H14CO3- were rapidly separated from the medium by centrifugation through silicone oil into a strongly basic terminating solution. Samples of these inactivated cells were assayed to determine total 14C accumulation, and acid-treated samples were assayed to determine 14C fixation. The rate of transport of inorganic into illuminated cells was faster than the rate of CO2 production in the medium from HCO3- dehydration. This evidence for HCO3- transport in these cells is in agreement with our previous results based upon measurements of photosynthetic O2 evolution. A substantial pool of inorganic carbon was bulit up within the cells presumably as HCO3- before the onset of the maximum rate of photosynthesis. Large accumulation ratios were observed, greater than 1,000 times the external HCO3- concentration. Accumulation did not occur in the dark and was greatly suppressed by the photosynthesis inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethyl urea and 3-chloro-carbonylcyanide phenylhydrazone. These results indicate that the accumulation of inorganic carbon in these cells involves a light-dependent active transport process.

Bicarbonates↗